Differential – Complete Unit Including Brakes Drums
Options			For These Cars
Alfa #	Ratio			Series	Model	1st Chassis	Last Chassis	Comment
1365.32.722	9/41	4.56	{	750C	Berlina	1st	1488.24930  (Last 750C)	750 Shop Manual  lists change from left  axle tube shim to   bearing shim:  after 1488.03685  Footnote 1
1365.32.767	8/41	5.12
1365.32.768	10/41	4.10
1365.32.739	9/41	4.56		750D	Spider	1st	1495.00500	Comment above … after 1495.00373
1365.32.740	10/41	4.10	{	750E	Sprint V.	1st		Comment above … after 1493.00658
1365.32.754	9/41	4.56		101.20	SS	1st	10120.00100
1365.32.773	8/41	5.12
1365.32.753	10/41	4.10	{	750F	Spider V.	1st	Last 750F	Comment above … after 1495.00373
1365.32.754	8/41	5.12
1365.32.755	9/41	4.56
1365.32.760	9/41	4.56	{	753	t.i.	1st	1468.177750  (Last 753)
1365.32.760	8/41	5.12
1365.32.760	10.41	4.10
1365.32.709	9/41	4.56	{	750B	Sprint	1st	Last	Comment above …. after 1493.02584  Footnote 2
				750D	Spider	1495.00501	Last
1365.32.771	8/41	5.12		750B	Sprint	1st	Last
1365.32.772	10.41	4.10
101.00.17.001.00	9/41	4.56	{	101.00	Berlina	1st	Last
101.00.17.001.01	10/41	4.10
101.00.17.001.02	8/41	5.12
101.11.17.001.00	9/41	4.56	{	101.11	t.i.	1st (101)	Last
101.11.17.001.01	10/41	4.10
101.11.17.001.02	8/41	5.12

1 What was the design change? 

“The systems of distance washers, for the right settlement of rear axle wheelworks, has been modified ……(then is lists  vehicle serial numbers provided in the chart) 

In consequence, while the fitting up of the pinion on the cage is unvaried, on the contrary the assembling procedure of the  differential group is changed for post-modification axles.” 

Then it describes the new procedure. Apparently, the change only impacts the Carrier Bearing Preload. 2 Owner of two 1955 Sprints report: 1493.00356 has no drain plug & fewer ribs than later unit, while 1493.01405 has drain  plug

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750-101 Differential Page 10 Model & Ratio Choices by Alfa # 

Differential – Complete Unit Including Brakes Drums
Options			For These Cars
Alfa #	Ratio			Series	Model	1st Chassis	Last Chassis	Comment
101.22.17.001.00	9/41	4.56		101.22	Station   Wagon	1st	Last
101.20.17.001.03	9/41	4.56	{	101.20	SS	101.20.0010 1	?	Only 2-shoe brakes
101.20.17.001.04	8/41	5.12		101.26	SZ	1st	?
101.20.17.001.00	9/41	4.56		101.20	SS	?	?	Only 3-shoe brakes
101.20.17.001.02	8/41	5.12		101.26	SZ	?	?
101-1600
101.12.17.001.02	8/41	5.12	{	101-1600	Sprint	1st	Last
				101-1600	Spider	1st	?
101.21.17.001.00	9/41	4.56		101-1600	SS	1st	?	Includes Veloce   brake drums
101.21.17.001.01						?	Last	With disk brakes
101.18.17.001.00	9/41	4.56		101-1600	Spider   Veloce	1st	Last	Includes Veloce   brake drums
101.23.17.001.00	8/41	5.12		101-1600	Spider	?	Last	With disk brakes

9.6.1 Later Differentials 

The following was provided by others and not personally verified by author. 

Options			For These Cars
Alfa #	Ratio			Series	Model	1st Chassis	Last Chassis	Comment
	7/41	8.86		105	GTA			Footnote 3
	7/43	6.14
	8/41	5.12
	8/43	5.38
	9/41	4.56		115	Spider		Up to 1981
	10/41	4.10		115	Spider	1983

3 Gordon Raymond: The 7 tooth pinions were very small and there was little contact area. These ring and pinions had life  expectancies of a few races. Since the 43-tooth pinion was being made it is safe to assume that a 4.30 10/43 ratio was also  available but I (unknown author) have not seen it on a USA car.

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750-101 Differential Page 11 General Education 

10 General Education 

10.1 Differential Terminology 

The following was assembled from Internet sites of differential manufacturers.  

	Definition	How to Adjust		How to Verify
Pinion   Depth	It is the depth of the pinion in  relation to axle centerline. It is  important that pinion depth is set  properly to avoid noise and/or gear  failure. Footnote 4	It is adjusted by adding or   subtracting shims to move pinion in  or out.		There is a specification, but  it is better to verify by  tooth contact pattern.
Pinion   Bearing   Preload	Is the amount of rolling resistance  on the Pinion Bearings. It is  important preload is within spec.  Pinion bearings will fail quickly if  over-preloaded.	It is adjusted by adding or   subtracting shims located between  Pinion Bearings.		It is verified by factory tool  or rotating the pinion with  an inch lb. torque wrench.
Carrier   Bearing   Preload	It is the total amount of rolling  resistance from the two Carrier  Bearings. If preload is too loose, it  will allow Backlash to constantly  change. If too tight, bearings will  fail quickly.	It is adjusted by adding or   subtracting shims.  It is set simultaneously with  backlash.		By “feel”.  Total Preload (Pinion,  Carrier & Gears) is verified  as above
Backlash	It is the free-play (working   clearance) between the Pinion and  Ring Gear. The space between the  teeth to allow for thermal   expansion and correct lubrication  of the mating teeth. It is   important backlash is within spec  to allow smooth operation and  proper lubrication.	It is adjusted by moving the carrier  left or right with shims.  It is also adjusted by changing the  Pinion Depth.		It is checked with a dial  indicator by rocking the  Ring Gear by hand.

4 CAUTION: factory tools do not measure to the “centerline”, but to a reference point. More in Special Tools section.

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750-101 Differential Page 12 General Education 

10.2 Pinion Depth & Preload 

Basic definitions were in the chart in the previous section, but this is a critical subject and worth a more detailed  understanding before going any further. The “How to Adjust” column in that chart stated that it is accomplished  with shims. Where these shims are located, at least for 750-101 cars, is shown in the illustrations below. 

Contrary to what the shop manuals imply, set the Depth first, because the Depth has much more influence on the  Preload than the Preload has on the Depth.

Pinion Depth  • Objective: mesh the Pinion Gear and Ring Gear in a  manner that provides quiet running.  • How: move the Pinion Gear in or out until it meshes  the middle of its teeth with the middle of the Ring  Gear teeth.  • Process: since the differential case fixes the reference  point and fixes the position of the pinion bearing; it  must be done by moving the Pinion Shaft & Gear  relative to the bearing.  • Method: change shims between the Pinion Bearing  @ Gear and the Pinion Gear.  • Caveat: since the Pinion cups are locked in position  by the differential case; when Pre-load is changed, it  will cause some change in the amount the bearing  cone entered the cup: therefore, changing the Depth.  Likewise moving Carrier Bearing shims between RH  & LH changes the Depth. Anticipate going through  multiple iterations of both adjustments.

• Decrease Depth (you are moving Pinion closer to  Ring Gear) – use thicker shim  • Increase Depth – use thinner shim

Pinion Preload  • Objective: create the right rolling pressure of the  bearing cone against the bearing cup. Too little and  bearing will cause vibration and noise. Too much  and bearing will over heat leading to spalling of  rollers and cups as the lubrication is pushed out of  the way.  • How: the tapered bearing cone is squeezed into the  tapered bearing cup. The tighter the squeeze the  more rolling resistance there is.  • Process: since both bearing cups are locked in  position by the differential case and the tapers are in  opposite directions; pulling the cones toward each  other increases the Preload of both bearings at once.  • Method: to control the amount of Preload, a fixed  length shaft sleeve plus shim(s) are placed between  the bearings. The result is that now both the cups and  the cones are locked in position with constant rolling pressure. The bearing industry labels this “fixed  position preload”.

• Decrease Preload – use thicker shim • Increase Preload – use thinner shim

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750-101 Differential Page 13 General Education 

10.2.1 Preload Q&A 

Question #1: doesn’t the above discuss miss a 2nd source of preload? That the inner bearing cone will be  pulled deeper into its cup as the Pinion nut is torqued to specification? Since the specification allows a wide  range of applied force (50-100 ft-lb.); wouldn’t applying 100 ft-lb. pull it deeper into the cup (increasing  preload) than if only 50 ft-lb. is applied? 

Answer: Torque does stress the Pinion Shaft/Gear, but the specified range of torque is not enough to  overcome the force needed to move the bearing significantly. 

Question #2 The housing is aluminum and all the other parts are steel. Since aluminum expands more than  steel; as the assembly warms up in use, wouldn’t the preload increase? 

Answer: Yes, but Alfa should have taken care of this with their specifications. 

10.3 Carrier Preload & Total Preload 

Carrier Preload  • Objective: same as Pinion Bearing Preload • How: same as Pinion Bearing Preload  • Process: since both bearing cones are locked in  position by the “differential” (sun wheel & spherical  planet wheel) and the tapers are in opposite directions; pulling the cups toward each other creates  Preload of both bearings at once.  • OEM Method: to control the amount of Preload,  shim(s) are placed under the cups. The result is that  now both the cups and the cones are locked in  position with constant rolling pressure. NOTE: an  alternative location for the shims will be discussed later, but it doesn’t not change the adjustment theory.

Total Preload  This is simply the accumulated rolling resistance of Pinion and Carrier bearing and the Pinion teeth against the  Ring Gear teeth.

10.4 Bearing Terminology 

10.4.1 Numbers 

Alfa uses, for various application, imperial (inches) and metric sizes bearings. In rare cases one dimension  might be Imperial and others metric. 

• There are different numbering standards for imperial, metric, and “Inch numbering system to identify  metric dimensioned and metric tolerance for inner race and outer races”.  
• There are different numbering standards for ball and tapered roller bearings.

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750-101 Differential Page 14 General Education 

• Numbering standards have evolved over time. The most recent big change was 1977. Most  manufactures have now adopted, at least to some extent, the international numbering standards. An  example of “to some extent”, is TIMKEN; which did not renumber many of their bearings. 
• ABMA (American Bearing Manufacturers Association) specifies measurements in inches. • ABMA assigns a separate number to the cup and the cone. To purchase the complete bearing,  both parts must be ordered. 
• ISO (a French acronym that translates to International Organization for Standardization) specifies  measurements in millimeters; however, in the USA most are converted to inches for listing. • ISO assigns one number to the bearing unit. 
• The numbering systems are complicated, probably not important for our use. 

10.4.2 Tolerance 

Greg Hermann (from correspondence, consolidated by author) 

The ABEC (Annular Bearing Engineering Committee of the American Bearing Manufacturers  Association) lists tolerance for the width (think ‘height’) of a tapered roller bearing as between 0.006 – 0.008″ of variation!! 

While this might be unimportant in a front wheel bearing, it has a large impact on setting up a differential.  Pinion bearing which are to be adjusted to the specification within 1/100th of millimeter (0.0004”) 

Consider how rapidly small tolerances on roller diameter, on the inside taper on the outer cup, the outside  taper on the inner cup, and on the relevant ends of each cup add up. The ID and OD of the cups have an  effect on height–because a change in these affects the amount of press fit needed to install the bearing,  and a lighter/heavier press fit will alter the diameter of the tapered surface it is adjacent to when the  bearing is installed!! 

The bearing’s width is the dimension which affects gear mesh pattern and bearing preload. So–if ANY of  the four bearings are replaced (the rear wheel bearings are NOT subject to this commentary), the set-up  MUST be checked and often re-set.  

10.4.3 Clearance 

Clearance provides the bearing room for expansion between the bearing cups and will add a small amount of  play between the two rings. An example of where a larger clearance is required is if a bearing is likely to get  hot. The heat needs room to escape otherwise there is a risk of bearing failure. 

C2	Clearance is less than international standard
No Markings	Standard Clearance
C3	Clearance is greater than international standard
C4	Clearance is greater than C3

10.4.4 Forms of Damage 

NTN bearing website listed 16 different types of bearing damage. I found it interesting that they had a  category for exactly what I saw on the bearing in the differential that was the subject of this article. Fretting surfaces wear producing red rust-colored particles that form hollows. Cause: If a vibrating load  works on contacting elements resulting in small amplitude oscillation, lubricant is driven out from contact,  and parts are worn remarkably.

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750-101 Differential Page 15 General Education 

10.4.5 Measurements – Complication 

• Standard description is ID x OD x W. 

Nominal   measurements:

Specification sheets:

WARNING: Nominal measurements are rounded to  whole number. “W” can be particularly confusing.  While ID and OD will measure with 0.01 mm of the  nominal. W can be significantly different. More  problems are caused by, apparently, some  manufactures using W = T and others using W = C.  This can cause problems in obtaining the correct  bearing. Example:   • The original Pinion Bearing @ Gear was RIV  05+06/2822 with measured dimensions 30.00 x  61.99 x 23.83.  • A national bearing house supplied, based on their  ID & OD measurements, sold the author NTN  33206, but it measured 30.00 x 61.99 x 25.12  • W is too much and would require a machinist to  reduce the width.  • NTN 32206 is 30 x 60 x 21.25, which will work  by using a thicker shim

It is best to ignore the W and verify that the “T” value is what you need. Go to the vendor’s catalog (sample  below) and examine it carefully. For example, 30206, 33206 and 33306 have ID 30 and OD 62; but only  33206 with “T” of 21.25 is close to the “T” of the original RIV brand inner Pinion Bearing. 

Inner  Diameter  (d)  mm

Simplifie d  Reference

NTN  Referen  ce

Outer  Diameter  (D)

Inner  Ring   Width  (B)

Outer  Ring   Width  (C)

Total  Wide  (T)

Max  Shaft   Link   Radius  (ras max)

Max  Housing  Link   Radius  (r1as max)

Weight Dynamic Load   Capacity  (y C)

Statis  Load   Capacity  ((y CO)

Limit  Speed   with   Grease  lube.

Limit  Speed   with   Oil lab.

mm

kg

kN

RPM

The illustrations below depict a few ways a roller bearing cup and cone could be constructed. Just because  two bearing have the same number does not mean the vendor designed them identically. The old bearing  might be like the one on the left and the new bearing like one of the others. 

Later, this document will discuss estimating bearing shims (if a bearing is replaced). The method of  measurements needed for the calculation will depend on the way the bearing is constructed.

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750-101 Differential Page 16 General Education 

10.4.6 Cup Angle 

This will not normally be found in the bearing vendor’s specification, but it is important for selecting the tool  into install the bearing cup.  

10.4.7 Country of Origin 

NTN still appears to make all bearing in Japan, and they appear to be of very high quality. 

Unfortunately, many old established brands are now outsourcing some bearing. 

• Timken – many are now Chinese 
• SKF – some are Chinese 
• FAG – last purchase by author was from Portugal instead of Germany. 

10.5 Bearing Shims 

Bearing shims are used to compensate for bearing dimensional tolerances (discussed above). 

Bearing shims are used to compensate for other variations, such as the Pinion machining tolerances. 

Shims can be placed under the bearing cup or the bearing cone. Alfa did some of each and changed the position  over the years. 

Later in this document, it will be recommended for 750-101 differentials that an additional change in shim position  be made during rebuild, if the Carrier Bearings are replaced. Why? Because without the factory tool it is almost  impossible to extract the LH Carrier Bearing from the axle tube without damage. Since replacing this bearing will  almost certainly require going through multiple iterations of experiments on shim thickness; a different solution is  needed. 

10.5.1 Alfa’s Proprietary Shims 

CAUTION: Alfa apparently used a proprietary ID for the Pinion Depth shim. This was to accommodate a  rather large radius in the machining of the shaft. 

• Alfa’s original shims have an ID 31.6 mm. 
• Readily available shims are ID 30 mm, but this will not work (see photos below) 
• Instead use 1 ¼ x 1 ¾ inch shims.

The Radius

Original Alfa shim:

Standard 30 mm shim  This shim will be mangled when  the bearing is fully pressed on

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750-101 Differential Page 17 General Education 

10.5.2 Tolerance – Shims 

• Shims also have a tolerance range. Below is the range from one quality vendor. 

Nominal	0.1	.02	0.3	0.5	1.0
Plus	0	0	0	0	0
Minus	0.03	0.04	0.05

• Since Alfa specifies the Pinion “Preload” and “Depth” to 1/100th of a mm, you will need to measure  shims. 
• Measure the shim (or shim stack), rotate to a different segment of the circle and measure again. While  these are called “precision shims”, you will find slightly different readings at different spots. Use an  average of what you find. 

10.5.3 Measuring Thickness 

If there is a stack of shims, it appears more accurate results are obtained by measuring the stack; instead of  measuring each shim and adding up the results to obtain the total. 

10.5.4 Estimating What is Required 

If you change either Carrier Bearings or either Pinion Bearing, the associated shims will have to be resized.  The following discuss covers methods for making an initial estimate of thickness of shim(s). These methods  get you close to what is ultimately needed. Final adjustments are likely, and complicated; that will be  covered in the Differential Rebuild sections later. 

Two methods are available for making an initial attempt to calculate what will be needed: • “Lead Shim” Trick 

• Calculation Method 

Carrier Bearings	Preload	only the Calculation Method is viable.
Pinion Bearing @ Gear	Preload	in theory either should work, but the author found that the  amount of force required to pull the bearing against the lead  ring to form the “shim” made the method not practical.
Pinion Bearing @ Flange	Depth	“Lead Shim” works very nicely.

10.5.4.1 “Lead Shim” Trick  

The “Lead Shim” trick basically replaces the actual controlling shim with a ring made from non-flux (solid  wire) solder. The unit is then slowly tightened until a specification (Pinion depth) is reached. Then the lead  shim is measured, a stack of actual shims of the same dimension is then installed. Below are the procedural  steps. 

“Lead Shim” Trick Method – Depth 

• Obtain non-flux (solid wire) solder, for example, 50-50 (50% tin and 50% lead), which is  approximately 3 mm thick. 
• Create a ring with ID approximating the target shim’s ID 
• Place lead ring on shaft where actual shim(s) will eventually go. 
• Oil shaft where bearing will go. 
• Using appropriate driver and hydraulic press, press the Pinion Bearing @ Flange just until it comes in contact with the lead ring. 
• Install Pinion-Shaft/Gear into cavity. 
• Install Pinion Depth Test Plate to keep the Pinion Shaft/Gear centered. This is in place of the  Pinion Bearing @ Flange. 
• Install the driveshaft flange or a flat plate (without slinger or seal) 
• Install washer and Slotted Shaft Nut, tightening finger snug. 
• Install factory Preload Test Tool (C.5.0100 or alternative). 
• Now cycle between testing the Preload, tightening the Slotted Shaft Nut a little, retesting Preload;  until the correct Preload is reached. 
• Remove the Bearing without damaging the “lead shim” you have created. 
• Measure the “lead shim”. 

CAUTION: review the photos below about not including the part that squeezes down into the  groove cut in the Sleeve / Shaft joint.

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750-101 Differential Page 18 General Education 

• Assemble a stack of real shims to match the measurement. 

10.5.4.2 Calculate Shim – Method 

In the following discuss the word “height” will be used instead of “width”. Two reasons: (1) it is more  intuitive, (2) because of where the shim is placed with Pinion Bearings the measured height can be  different than the bearing’s defined width (ID x OD x W). 

• While the measurement is always the cone to cup distance (“T” of the earlier Terminology  discussion), if the old and new bearings are of different design it is easy to make an error during  measurement.

	The differential used for this document had these types:  • Pinion Bearing @ Flange – type A • Pinion Bearing @ Gear – type C • Carrier Bearing – type B
Example:

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750-101 Differential Page 19 General Education 

Step 1 

• Using a surface plate and depth micrometer to determine the exact height of the old and the new  bearings. 
• CAUTION: How to determine height depends on how bearing is constructed: • If type A, B, or C (illustration above) set the cone on the surface place and then the cup on the  cone. 
• If type D place two pieces of thick shim stock (or 1-2-3 blocks) on surface plate. Then the  cup on the shim stock. Then place cone into cup, verifying that cone does not touch the shim  stock or the surface plate. 
• Not sure type E exists. 
• CAUTION: Where to make the measurement depends on the above decision: • If cup is on the top, measure on the cup. 
• If the cone is on the top, measure on the cone. 
  

Step 2 

On cup		On cone
• “Zero” the micrometer on the  surface plate  • Add a weight to the bearing to  prevent the cup from tilting on  the cone during measurement  (without the weight I was having  0.01-0.02 inconsistency in   measurements)  • Record both old and new values.  Example:   this new bearing is 0.04 mm taller.	Original Bearing		New Bearing

• Consider a height adjustment to compensate for wear on old bearing 

An experienced rebuilder (not the author) suggested adding 0.03 mm (approximately 0.001”) to  old height to compensate for wear. 

Step 3 

• Calculate height adjustment for different height of old bearing compared to new bearing. Step 4 
• Consider a height adjustment for dimensional change due to “press fit”. 

An experienced rebuilder (not the author) suggested if there are difference in ID or OD of the old  versus new bearings, then allow +/- 0.02 mm for height change caused by the press fit. Why? Because the final height will change based on how amount of “squeeze” that will occur  when the bearing is forced into place.  

Step 5 

• Measure the thickness of the original shim stack (be careful not to measure a damaged area of the  shim) 
• Adjust the shim stack thickness to compensate for this bearing height difference. • Dilemma: Alfa offered a limited set of shim thicknesses, what to do if they do not exactly match what is needed? Possibly the answer is “make your own” from shim stock.

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750-101 Differential Page 20 General Education 

Example 1: ID and OD – No Change 

• Step 1 (measure height) 

	Original Bearing	New Bearing
Height	15.93	15.89

• Step 2 (wear adjustment) 

	Original Bearing	Condition	Wear Adjustment  (either 0 or +0.02 mm)	Original   Adjusted
Height	15.93	Significant wear	+0.02	15.95

• Step 3 (adjust for old versus new) 

	Original  (Adjusted)	New	Difference	Impact on  New Shims	Height   Adjustment
Height	15.95	15.89	-0.06	Need thicker	+0.06

• Step 4 (adjust for press fit) 

	Original	New	Difference	Impact on  Installed Heights	Press Fit   Adjustment
ID	24.97	24.97	0	None	0
OD	61.94	61.94	0	None

• Step 5 (calculate shims) 

Original  Shims	Height  Adjust	Press Fit  Adjust	Calculation	Total of Shims  to Install
0.390	+0.06	0	0.390 +.06 + 0 =	0.45 mm  (increase of   0.06)

Example 2: ID or OD – Changes 

• Step 1 (measure height) 

	Original Bearing	New Bearing
Height	23.05	22.72

• Step 2 (wear adjustment) 

	Original Bearing	Condition	Wear Adjustment  (either 0 or +0.02 mm)	Original   Adjusted
Height	23.05	Significant wear	+0.02	23.07

• Step 3 (adjust for old versus new) 

	Original  (Adjusted)	New	Difference	Impact on  New Shims	Height   Adjustment
Height	23.07	22.72	-0.33	Need thicker	+0.33

• Step 4 (adjust for press fit) 

	Original	New	Difference	Impact on  Installed Heights	Press Fit   Adjustment
ID	30.00	30.00	0	None	+0.02
OD	62.05	61.99	-0.06	New shorter

• Step 5 (calculate shims)

Original  Shims	Height  Adjust	Press Fit  Adjust	Calculation	Total of Shims  to Install
0.980	+0.33	+0.02	0.980 +.33 +.02 =	1.33 mm  (increase of   0.35)

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750-101 Differential Page 21 General Education 

Worksheet:  

• Step 1 (measure height) 

	Original Bearing	New Bearing
Height

• Step 2 (wear adjustment) 

	Original Bearing	Condition	Wear Adjustment  (either 0 or +0.02 mm)	Original   Adjusted
Height

• Step 3 (adjust for old versus new) 

	Original  (Adjusted)	New	Difference	Impact on  New Shims	Height   Adjustment
Height

• Step 4 (adjust for press fit) 

	Original	New	Difference	Impact on  Installed Heights	Press Fit   Adjustment
ID
OD

• Step 5 (calculate shims) 

Original  Shims	Height  Adjust	Press Fit  Adjust	Calculation	Total of Shims  to Install

10.6 Assembly Lubricants 

The following is from Workshop Manual – Spider (1985) 

For	Alfa Spec	Industry Spec	Equivalent
Axle Assembly “Pin” – to  Reaction Triangle	ISECO Ergon Rubber Grease n0 3		Any “red rubber”  grease
• Flange – area for seal • Pinion seal – internal lip • Axle seal – internal lip	ISECO Molykote BR2   (Dow Corning)	DIN 51 818 = NLGI • Consistency class 2 • Mineral oil  • Lithium soap  • Solid lubricants  • EP additive  • Corrosion inhibitor	Dupont Molykote
Seals – outer edge	Shell Spirax HD 80W90	GL-4, GL-5, MT-1	• Any oil  Some suggest   silicon sealer

10.7 Assembly Sealants 

The following is from Workshop Manual – Spider (1985) 

For	Alfa Spec	Industry Spec	Equivalent
Ring Gear Bolts	Dry	N/A	Definitely consider  Loctite #271
Pinion Splines	(Obsolete products)  • 1974/12 Service Bulletin   specified Loctite 27 for 105 &  115 cars.   • 1985 Shop Manual: Loctite 242		Loctite 648 sleeve  retainer
Axle Tubes @ differential  case	Perfect-Seal LOWAC adhesive (but #3 or #4?)		See below

10.7.1 Gasket – Don’t Use 

Do not use a paper gasket between the aluminum housing and the steel wheel shaft, because this will  disrupt the critical Carrier Bearing Preload. 

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750-101 Differential Page 22 General Education 

10.7.2 LOWAC Substitutes 

Note: Henkel owns both Loctite name and Permatex name.  

10.7.2.1 Loctite 515 

LOCTITE® 515™ (38655) cures when confined in the absence of air between close fitting metal surfaces.  It seals close fitting joints between rigid metal faces and flanges and will flex with minor flange  movements. The product is designed for close fitting flanged parts with gaps up to 0.25 mm (0.01 in). 

Loctite Technical Advisor 

• Spray the castings with Loctite “Klean ‘N Prime” (dry for 3-5 minutes) 
• A thin layer of Loctite 515 on flange. 

Note: Loctite 515 is for steel and aluminum, while Loctite 518 518 is only for aluminum. Both are  products that are designed for metal-to-metal assemblies 

10.8 Oil 

Model	Alfa Spec.	Industry Spec.	Type	Qty.
• 750  • 101-1300  • 101-1600	Shell Spirax 90 EP  (replaced by Spirax 90 HD)	SAE 90 API EP	GL4	1.25 kg  3.0 pints (US)
• 105-1600  • 105-1750  • 115	Shell Spirax 90 HD	SAE 90 API GL5 EP	GL5

10.8.1 EP 

“EP’” stands for ‘Extreme Pressure’ and is a term used to describe lubricant applications that are subjected to  high load conditions. Additives, both physical and chemical, are used in grease formulations to give a product  its high load capabilities or ‘EP’ performance. 

10.8.2 HD 

“HD” does not appear to have any specific meaning. 

10.8.3 GL4 vs. GL5 

GL5 has roughly twice the amount of EP additives compared to GL4, 

10.8.4 Brands 

The following has been provided by others and has not been personally verified. 

• GL5 is safe for the 750-101 differentials 
• Newer lubricants provide improved gear protection. Any GL4 will do, but the newer lubricants have  better gear protection and lubricity. I would suggest most any GL5 synthetic. If you have a bit of gear  noise, try Redline’s “Heavy ShockProof®” – film thickness greater than an SAE 75W250, yet low fluid  friction like 75W90. The microspheres in the lubricants will further protect worn gear surfaces.

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750-101 Differential Page 23 Design Changes 

11 Design Changes 

11.1 Drain Pan 

Tony Stevens, Alfa Stop: for the early 750, the “bottom plate” did not have a drain plug like all later differentials. 11.2 Carrier Bearing Shim Position – from Axle Tube to Bearing Cup The first 750 Series differentials used an adjustment shim between the left axle tube (“big flange”) and the main  aluminum casting. Later differentials used an adjustment shim under the left Carrier Bearing. Both appear in the  Spare Parts Catalog, without any reference to when used or that both types are not used. However, the 750 Shop  Manual lists the change (see Model & Ratio Choices by Alfa # section)

	Believed to be shims for original design

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750-101 Differential Page 24 Design Changes 

11.3 Pinion “Dept” Shim – from Cone to Cup 

• 750-101 placed the shim under the cone 
• 105, at least according to 105 Shop Manual, moved the shim to under the cup. 

11.4 Pinion Gear Width 

Pinion
			This is a critical measurement for setting Pinion “Depth”  “A” has changed over time:  • During 750 series from 32.5 to 34.5 mm  • When ?????  • During 105 series from 34.5 to 35.5 mm   • Apparently during 1969
Alfa #  Ring Gear &   Pinion	Ratio	Ring   Gear  Bolt   Holes	“A”	Series	Model	1st Chassis	Last   Chassis	Comment
1365.32.707	9/41	8.5	?	750	All	1st	?	? 32.5 to 34.5   mm ?
1365.32.726	10/41			750	• Sprint  • Sprint V. • Spider  • Spider V	1st	?
1365.32.733	8/41			750	Sprint  Sprint V.	1st	?
1365.32.757	8/41	9.25	?	101-1300	All except  Spider	After   above	Last	? 32.5 to 34.5   mm ?
1365.32.758	9/41			101-1300	All
1365.32.759	10/41			101-1300	All except  SS & SZ
105.00.17.021.03	9/41	9.25	34.5	101-1600  Footnote 5	SS	1st	Last	A = 34.5   Footnote 6
105.02.17.021.01	8/41	9.25	?	101-1600	Sprint  Spider	1st	Last	? 34.5 to 35.5   mm ?

11.4.1 Pinion “Depth” 

• When width (“A”) changed, so did the “Depth” specification. 
• Pinion “Depth” is the distance of the pinion to axle centerline. 

CAUTION: the Shop Manual specification and the factory tool do NOT measure to the centerline. The actual method will be discussed in the Differential Rebuild / Pinion-Shaft/Gear Part 2 section. 

Series	Pinion Width	Centerline	Measuring Spec
Early 750	32.5	59	72
• Late 750  • 101-1300  • 101-1600  • Early 105	34.5	57	70
Late 105	35.5	56 (not verified)	69 (not verified)
115	?	58.5 +/- 0.03	71.5

5 Also 105 Sprint GT and GTV 

6 According to Info Sheet 17.69.4.1 (1968/10/20)

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750-101 Differential Page 25 Design Changes 

11.5 “Housing – Differential”

“Housing – Differential” (Alfa term)
For 750/101-1300 there were four “Housing”, which is not the external aluminum case, but the unit the Ring Gear is bolted to.
At 6:00 position is Alfa #, close up in next photo
Alfa #	Ring   Gear  Bolt   Holes	Series	Model	1st Chassis	Last Chassis	Comment
1365.31.001	8.5	750B	Sprint	1st	1493.02500
		750C	Berlina	1st	1488.03200
		750D	Spider	1st	1495.00500
1365.31.009	8.5	750B	Sprint	1493.02501	?	Speculation, the  change is either:  • Moving shim   from axle tube   shim to bearing  • Pinion Gear   dimension “A”
		750C	Berlina	1488.03201	?
		750D	Spider	1495.00501	?
		750E	Sprint V.	1st	At least by   1958/08 750E  1493.06920
		750F	Spider V.	1st	?
1365.31.011	9.25	• 750  • 101-1300	All	At least by   1958/08 750E  1493.06920	Last	As found on   1493.6920
105.00.17.200.01	9.25	101-1600	All	?	Last
105.16.17.043.00	9.25			Optional	Optional	Self-locking   differential

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750-101 Differential Page 26 Design Changes 

11.6 Ring Gear Bolts 

See chart in previous section for when bolts changed from 8 mm to 9 mm during the 750 series. 

Spare Parts Catalog lists the 9 mm bolt as 9 x 1 x 22.5; however, what was found on 1943*E*06920 was 9 x 1 x 17. 

Bill Gillham: 

Even with the switch from M8 to M9 bolts during the 750 series; they have been found to be too weak. I  have looked in four rear ends in the last month, all had loose bolts, all had at least one bolt head sheared  off and one differential was down 4, with the other 4 loose. We replaced all original M9 bolts with 105  Ring Gear bolts (12.9 hardness) and red Loctite. We now check every rear end that comes into the shop. 

Torque specs say “dry”, but I’d say “with red Loctite!”. 

Author: 

The weakness may be due to the original bolts being too short. See photo 

Coming loose may be caused by the bolts sitting in an oil bath. 

NOTE: 9 x 1.0 bolts are unusual and not generally available. See Hardware section for sources.

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750-101 Differential Page 27 Evaluation – Prior to Disassembly 

12 Evaluation – Prior to Disassembly 

12.1 Axle 

12.1.1 Seal 

Visual check of seals for leaking. 

• Probably should consider replacing if doing any other work to differential. 

12.1.2 Axle (Wheel) Bearing 

Evaluate bearing condition. 

• Rotate slowly and feel for roughness, while listening for noise. 
• Rotate quickly and listen for noise 

Unfortunately, the noise could be from any of the bearings, so listen carefully. 

12.2 Pinion  

12.2.1 Seal 

Visual check of seals for leaking. 

• Probably should consider replacing if doing any other work to differential. 

12.2.2 Pinion Bearing 

• Rotate slowly and feel for roughness, while listening for noise. 
• Rotate quickly and listen for noise 

12.3 Carrier Bearing 

Evaluate bearing condition. 

• Rotate slowly and feel for roughness, while listening for noise. 
• Rotate quickly and listen for noise 

Unfortunately, the noise could be from any of the bearings, so listen carefully. Try listening via the filler plug hole. 12.4 Ring Gear Teeth 

Visual check for excessive wear or chipped teeth via the filler hole and a good light. 

NOTE: The Ring Gear and the Pinion are factory matched and would have to be replaced as a unit. 12.5 Ring Gear Bolts 

These bolts can only be examined after the left (large bell) axle tube has been remove. 

HINT: review discussion in Design Changes / Ring Gear Bolts section. 

12.6 Decisions 

• Replace wheel seals? Do it yourself item 
• Replace axle (wheel) bearings? Do it yourself item 
• Replace pinion seal? Do it yourself item 
• Replace Pinion Bearings? See Can You Rebuild a Differential It Yourself? section • Bad gear portion of Pinion Buy a different differential 
• Bad Ring Gear? Buy a different differential 
• Replacing Ring Gear bolts? Do it yourself item 
• Replace Carrier Bearings? See Can You Rebuild a Differential It Yourself? Section

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750-101 Differential Page 28 Can You “Do It Yourself”? 

13 Can You Rebuild a Differential It Yourself? 

• Refer back to General Education section for why it is difficult to replace Pinion Bearings or Carrier Bearings. • Required tools is another major problem. 

Proceed cautiously. 

14 Special Tools 

The Giulietta Shop Manual lists 30 special tools, most of which were probably rarely seen outside of Italy, except in the  shop manual photos. Can you work on these differentials without them? – maybe.  

Can you built, or have built for you some necessary tool (review the next few pages)? In the rest of this section, tools  listed as Alternative Tool, will have construction diagrams in the Special Tools – Construction section.

Additional confuse is added by a tool change to match the change from an adjustment shim between the left  axle tube and the main aluminum casting; to an adjustment shim under the Carrier Bearing.
Before the modification 6123.27.025 includes both  #1 & #2 in photo:	Post modification 6123.27.025 includes only #2. Later apparently renumbered C.6.0115
Alternative techniques will be offered as a substitute for this elaborate tool.

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750-101 Differential Page 29 Can You “Do It Yourself”? 

Tools that you will need, factory or sourced other ways.

Pinion’s Slotted Shaft Nut Tools
750-101 era tool – 6121.01.166   (probably later labeled A3.0167)		115 era tool – A2.0246
750-101 era tool – 6121.20.035		Alternative Tool: make one from a 1” impact  socket (impact was used because they are made  from stronger metal … do NOT use impact  wrench).
Pinion Preload Tools – Also used for Backlash
6123.15.006 + 50 g + 60 g weights – 750  Apparently, the weights were to be locally sources.	C.5.0100 – 101 & 105
Alternative: is an Inch-lb. torque wrench

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750-101 Differential Page 30 Can You “Do It Yourself”? 

Pinion Bearing – Extract / Install Tools
There are a steel inserts in the housing that the Pinion Bearings cups are pressed into. The extraction tool  should rest against this steel insert and not the outer aluminum case.
Alfa specified several tools, here is  an example	Alternative Tool:   A – extract outer bearing cup  B – extract inner bearing cup  C + D + E– extract / install
Pinion cups – Install  • C, D, and E from above  • Generic shop tools bearing/seal driver →  • Pinion Bearing @ Gear: 63 mm / 160  • Pinion Bearing @ Flange: 60 mm / 160

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750-101 Differential Page 31 Can You “Do It Yourself”? 

Cone – Pinion Bearing @ Gear  • Alfa 105-115 tool A.30412  Alternative Tool: made from tubing (		Cone – Pinion Bearing @ Flange installation • Use the same driver (left photo)  • Alternative Tool: hold Pinion Shaft in place with  special wedge (the 750 Shop Manual instructs to  use a block of wood, but that doesn’t seem very  realistic).
RECOMMENDATION: the Shop Manual says to use  a hammer to install Pinion Bearing @ Flange. A rather  poor method for a bearing! Use a press. To support  the differential housing while using press, use 2 pieces  of wood, either side of center rib.
Pinion Seal
• Alfa 105-115 tool A.3.0167  • Generic shop tools: 75 mm or larger bearing/seal  driver

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750-101 Differential Page 32 Can You “Do It Yourself”? 

Pinion Depth Tools
“Zero” Indication Tool – 750
Un-numbered tool  Alternative: Mitutoyo Gauge Block – 70 mm McMaster-Carr 98525A125	6123.41.111 (Indicator stand)
Zero” Indication Tool – 101 & 105 tool
CAUTION: go to Factory Tool Bulletin section and review Information Sheet 17.69.4.1 (1969 /10/20)  which instructed service departments to alter this tool. If you are lucky enough to have this tool, examine it  closely to see if it was modified.  Actual height:  • For 34.5 70 mm  • For 32.5 72 mm	Above renumbered C.5.0116

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750-101 Differential Page 33 Can You “Do It Yourself”? 

Depth Reference Point Tool
750-101 Tool –  6123.27.028	105 Tool – C.6.0114		Alternative Tool: usable with bearing cup  installed or removed.   (part on left is much ticker than required)
Alternative Tool: Pinion Depth Test Plate Tool
Carrier Bearing Cone
Extract / Install Tool  Alternative Tool: Part 1 – Pusher  Part 2 – Stand  Protective stand for Carrier Bearing cone on opposite  side. You want the pressure on the central unit’s steel  tube that the Carrier Bearing cone is pushed onto  instead of putting the pressure on the bearing.  Looks basically the same, as the Pusher, but shorter		Extract – tool at left plus generic bearing splitter and  puller

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750-101 Differential Page 34 Can You “Do It Yourself”? 

Carrier Bearing Cup Extraction Tools
Alternative Tool: RH Cup (also used to extract /  install 750-101 driveshaft support bearing)	LH (large flange) Cup  No good replacement for the factory tool has been  found. Footnote 7
Carrier Bearing Cup Install Tool
Generic shop tools: 72 mm / 160 bearing/seal driver
Ring Gear Lock
Unnumbered Tool in Shop Manual	Alternative Tool:  (Drilled, tapped old filler plug)

7 The author tried a slide-hammer with a 3-jaw-cone-spread puller with no luck. Others have suggested a slide-hammer  attachments intended for pulling the rear wheel bearings out of the now ‘C-clip’ style, American rear axles. These things  have a pivot–so that they insert, and then turn to get a purchase on the inner face of the bearing’s outer cup. It would have to  be sized to match an Alfa bearing.

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750-101 Differential Page 35 Axles 

15 Axles 

Replacement of axle (wheel) bearing and seal can be completed without impacting “differential setup”. 15.1 Axle Removal 

• Remove nuts and washers from Axle retainers. 
• There is, of course, a factory tool, but the axles can be pulled slide hammer. 

15.2 Axle (Wheel) Bearing 

HINTS:  

• Before removing, mark the slot in the Slotted Shaft Nut and the washer’s tab where the bent over tab engages  the Slotted Shaft Nut. Then, since no torque value is provided by Alfa, simply snug up and then turn enough  more to re-engage tab in same Slotted Shaft Nut slot. 

CAUTION: do one axle at a time and permanently mark the axle and its backing retainer with: • “D” – Destro (right side)  

• “S” – Sinistra (left side). 
• Keep the tab washer and Slotted Shaft Nut with original side. 

• Carefully bend back the washer tooth that engages the Slotted Shaft Nut. 
• Remove the Slotted Shaft Nut 

750 era tool – 6121.20.035   101-era tool A.50120/1

Bearing splitter

• You will need a “bearing splitter” and hydraulic press to remove the bearing. 
• You will almost certainly have to remove the 4 studs from the backing retainer to provide access for a “bearing  splitter” under the bearing. They are10 x 1.0. Triple nuts will work. 
• If a lath or other method of suspending the axle is available, check that the axle is straight. 
• For specification see Differential – Rebuild / Specifications / Tolerances section 

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750-101 Differential Page 36 Axles 

CAUTION: don’t mix the axles and retaining rings – review the marks you added. 

• Reinstall the studs to the retainer. 
• Install the paper gasket onto the retainer 

CAUTION: align the gasket “weep slot” with the retainer’s “weep slot”. 

• Install the brake backing plate onto the retainer studs 

CAUTION: pay attention to front / back of brake backing plate so it is correct when installation is complete. CAUTION: align the backing plate “weep slot” with the retainer’s slot. The Veloce backing plate has two  “weep slots”, but only one will align properly. 

NOTE:  All other models have the rear wheel cylinder near the bottom of the plate instead of near the top.

• Install retainer & backing plate on to the axles shaft. 
• Oil the area where bearing will go 
• Using a hydraulic press install the new bearing onto the shaft. 

The factory tool can easily be replaced by a steel pipe  with:  • ID between 25-30 mm  • OD between 38-45 mm   • about 65 cm long.

• Install tab washer. 
• Install Slotted Shaft Nut. The originals were found to not be more than snugged up to washer and then turned  a little more. Tighten until your marks on the tab and Slotted Shaft Nut align. 
• Bend over one tab on washer. 
• Set aside for latter installation.

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750-101 Differential Page 37 Axles 

HINT: If you are going to rebuild the differential, wait until Final Assembly section to do the rest of these steps. 

15.3 Axle (Wheel) Seal 

HINT: If you pull the axle, always replace the seal. 

RECOMMENDATION: use a double lip seal instead of the original single lip seal. Both numbers are in Parts  Interchange section. 

Install new seal: 

• Smear a light coating of silicon sealer on interior of axle housing where seal will go, before installing seal. • Using appropriate bearing/seal driver, install the seal. Alfa tool: 6121.07.219 or A.3.0160. • Fill seal contact area with Molykote before installing axle. 

15.4 Axle Install 

CAUTION: don’t interchange right and left axles. 

• Install axles, being careful not to damage seal and to engage teeth in differential. 
• Using an aluminum bar against the axle, pound into place with a hammer. 
• Install washers and nuts on Retainers. 
• Torque to specification (see Torque section)

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750-101 Differential Page 38 Rebuilding Differential 

16 Differential – Rebuild 

CAUTION: Only disassembly pieces that were identified in Evaluation – Prior to Disassembly / Decisions section as  requiring it. Skip over other sections below. 

During “Evaluation”, if it was decided that the any of bearings or the Ring Gear bolts are to be replaced, follow the  additional evaluation procedures below. 

If only the pinion seal is to be replaced, skip to Final Assembly section. 

16.1 Review – Unit 

• Remove the axle tubes. 
• Lift out the differential assembly. 
• Prevent future leaks. 
• Examine the Axle Tube’s lip that connects it to the central aluminum case for rust or damage. • Examine the central case for corrosion or damage at this junction. 
• Clean up the mating surfaces as needed; being careful not to remove metal. This needs to remain as a tight joint. 

• Visual check for excessive wear or chipped teeth on Ring Gear 
• Visual check for excessive wear or chipped teeth on Gear portion of Pinon. 
• Visual check for excessive wear or chipped teeth on Side Gears (those 900 opposed gears in the center of the  Ring Gear assembly). 
• Verify no broken or lose bolts on Ring Gear (review Ring Gear Bolts section) 

(WARNING: retain original position of Ring Gear relative to differential unit) 

• Visually check Carrier Bearings for pits or scratches.

Example
	Comments from   experienced   differential rebuilder  (not the author):  This cup (outer race)  of the Carrier Bearing is TOAST. Not a   disaster yet, but it soon  would be. I’d bet that  the inner race looks  even worse.   You may well have one  or two Pinion   Bearings in equally  bad or even worse  shape.
The cups and rollers of all four bearing in the differential working on for this document had turned “brown”  and completely lacked “shine”.

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750-101 Differential Page 39 Rebuilding Differential 

• Spin the Pinon and listen for excessive noise. 
• Carefully paint both the “drive side” and “coast side” of all the Ring Gear teeth with “gear marking  compound”. 

• Reinstall Ring Gear assembly 
• Reinstall the left axle tube. 
• Torque nuts to prescribed value (see Torque section). 
• Rotate the Pinion 40 revolutions clockwise and 40 revolutions counter-clockwise. 
• Remove the left axle tube. 
• Take closeup photographs of the pattern on the Ring Gear. These will be used later for comparison. 

No photograph   Because I didn’t think to do it, hopefully this document will prevent others from making the same mistake.

• Safely store Ring Gear assembly in a plastic bag for now. 

16.1.1 Decisions 

• Bad Pinion Gear? – Buy a different differential. 
• Bad Ring Gear? – Buy a different differential. 
• Bad Side Gears? – Buy a different differential. 
• Bad Ring Gear bolts? – Follow procedure below 
• Bad Carrier Bearing? – Follow procedure below 
• Bad Pinion Bearing? – Follow procedure below 

In the following, skip over sections that do not apply because of these decisions. 

If you are going to proceed, you will need the following specifications

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750-101 Differential Page 40 Rebuilding Differential 

16.2 Specifications 

16.2.1 Tolerances

	750 Shop Manual	101 Enclosure to Shop   Manual	Glenn’s   (AR Repair & Tune-up   Guide)	105 Shop Manual	Comments
Axle   Eccentricity	Not to exceed:  0.10 – 0.15 mm	No comment		Not to exceed:  0.10 mm   (0.0039”)
Pinion   Bearing   Preload – with  Ring Gear   removed	Use 6123.15.006	No comment		Use C.5.0100	Details in   Rebuild   Differential  section
Pinion Depth	See Design Changes / Pinion Gear Width / Pinion Depth section for more information.
	Set to specified value  +/- value etched on  Pinion shaft.	No comment		Set to specified  value +/- value  etched on Pinion  shaft.	CAUTION:  105 manual   points out that  this is   measured to  100th of a   mm!
Pinion   Bearing   Preload –  with Ring   Gear removed	Use 6123.15.006,  with 600-gram  weight	No comment	(With seal installed) 0.145-0.195 m/kg  (0.14-0.19 newton/kg) (13-17 ft.-lb.)	Use C.5.0100 with  weight @ “P”   mark	Details in   Rebuild   Differential  section
Total Bearing  Preload –  with Ring   Gear installed	No comment	No comment	0.165-0.222 m/kg  (1.6-2.2 newton/kg) (14-19 ft.-lb.)	Use C.5.0100 with  weight @ “T”   mark	Details in   Rebuild   Differential  section
Backlash	@ Pinion Flange:  0.18 – 0.20 mm  (0.007 – 0.011”)  This provides actual  backlash:  0.05 – 0.10 mm  (0.002 – 0.004”)	0.13 – 0.18   mm	0.05-0.10 mm  (0.002-0.004”)	@ Pinion Flange:  0.15 – 0.25 mm (0.006 – 0.009”) This provides   actual backlash: 0.05 – 0.10 mm (0.002 – 0.004”)	Details in   Rebuild   Differential  section
Maximum   Ring Gear   Eccentricity	No comment	0.025 mm		No comment

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750-101 Differential Page 41 Rebuilding Differential 

16.3 Ring Gear Bolts 

If replacing bolts, proceed as follows one bolt at a time, working in a diagonal pattern: 

(WARNING: retain original position of Ring Gear relative to differential unit) 

• Carefully bend back tab on lock washer (they are not generally available, so if you plan to reuse be careful) • Remove a bolt and then thoroughly clean the threads in the housing (they will be oil soaked). • Use about 10 Q-tips, first dry and then soaked in alcohol to clean each hole. 
• Blow out with air. 
• Treat with Loctite “Klean ‘N Prime”, let dry for 5 minutes. 
• If reusing old bolts: 
• Install tab washer 
• Install bolt, with Loctite #271. 
• Torque to specified value (see Torque section). 
• If using 105 bolts, check the length in comparison to originals; then follow above or below • If using the www.heinbrand.com bolts: 
• They are 26 mm long, so add an appropriate thickness washer to eliminate the excess protrusion. 

Hein Brand bolt without accommodation:

With 2.9 mm thick washer and 0.5 mm shim  washer added:  Author used   Hillman   brand 3/16” x   1” “Thick   Fender   Washer”   (#885520)   drilled out   to 9 mm.   The sharp   edge from   drilling was   removed   before use.

• Discard the original tab washer 
• Make your own decision on the next issue. 

Hein Brand bolt has serrations. The author  believes this will impact the torque value.

Consider adding the stainless-steel shim washer to  compensate.

• Install bolt, with Loctite Red #271. 
• Torque to specified value (see Torque section). 

16.4 Carrier Bearings – Part 1 

Complete this section only if the decision in Rebuild Differential / Review Unit / Decisions section dictates it.

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750-101 Differential Page 42 Rebuilding Differential 

16.4.1 Things Not To Do! 

• Do not mix up the cone and cups from the two sides. Do one bearing at a time. 

WARNING:  Do not press on one bearing without a  protective stand in place for the opposite bearing (see photos for the disaster that happens  if you don’t).

• Do not lose or damage the shims during disassembly. Check shims for damage. If present, carefully  repair with hammer against a very smooth plate. 

• Do Not mix the shims from one location with another (put in marked bag and add to chart below)

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750-101 Differential Page 43 Rebuilding Differential 

• NOTE: this worksheet is used for both Carrier Bearing – Part 1 and Carrier Bearing – Part 2 sections. 

16.4.2 Worksheet 

Carrier Bearing Worksheet
Shims	Original	Lead Trick  or   Calculated Estimate	2nd Attempt	3rd Attempt	4th Attempt	5th Attempt	Final
RH Shims
1
2
3
4
5
Subtotal
LH (large flange) Shims
1
2
3
4
5
Subtotal
RH/LH Shim Ratio
Ratio
Gap Between LH Flange & Aluminum Case – When Preload Feels Right
Gap
Ratio Must Remain Constant
RH + LH

16.4.3 Decision Point 

Alfa placed the Carrier Bearing shims under the bearing cups. The LH cup is very difficult to remove without  damage. Therefore, consider an alternative method for the rebuild. Place the shims under the bearing cone,  as they are for both Pinion bearings. 

Obviously, this mean finding a new ID/OD-sized shims. See Hardware section for source.

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16.4.4 LH (large flange) Side 

16.4.4.1 Disassembly 

• Extract the Cup from the axle tube.  

CAUTION: Extraction from the “large flange” axle tube is very difficult to do without destroying  the cup. At the time of publication, the author has no good suggest on how to do this. 

• CAUTION: Add the size of each shim to the Worksheet – Carrier Bearing and then place shims  in a bag with a note of which side they belong to. 
• Extract the Cone from the differential using a “bearing splitter” and puller. 

16.4.4.2 Shim 1st Estimate– LH  

HINT: Use the Worksheet – Carrier Bearing to keep track of what you have done until you have exactly  what is needed. 

Use either the “Lead Shim Trick” method or the “Calculate Shim” method to make 1st estimate of required  shims. For the “Calculate Shim” method use worksheet found in  

General Education / Bearing Shims / Estimating What Is Required / Calculate Shim section. 16.4.4.3 Reassembly – LH 

• Lubricate steel flange where cup will be installed. 
• Lubricate the differential where the cone will be installed. 
• If decision was to use OEM shim position under cup, then: 
• Install shims into steel flange: 
• Using an appropriate size bearing/seal driver, pound bearing cup into flange. 
• Place the RH bearing cone on protective stand. 
• Using an appropriate size driver; press or pound bearing cone onto differential. 
• If the decision was to use the recommended alternative shim location, under the cone, then: • Using an appropriate size bearing/seal driver, pound bearing cup into flange. 
• Install shims onto differential unit. 
• Place the RH bearing cone on protective stand. 
• Using an appropriate size driver; press or pound bearing cone onto differential. 
• Now move on to the RH side. 

16.4.5 RH Side 

16.4.5.1 Disassembly 

• Push the Cup from the main aluminum casting. See Special Tools section for tool design. • CAUTION: Add the size of each shim to the Worksheet – Carrier Bearing and then place shims  in a bag with a note of which side they belong to. 
• Extract the cone using the same tools as the LH side 

16.4.5.2 Shim 1st Estimate – RH 

Same worksheets and process as LH side. 

WARNING: adjust this shim value to retain the original RH / LH shim ratio (see worksheet). 16.4.5.3 Reassembly – RH 

Same process as LH side, except the cup is installed in the aluminum housing. 

Be sure to place the LH Carrier Bearing cone on protective stand while installing RH bearing cone.

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16.5 Pinion-Shaft/Gear – Part 1 

16.5.1 Remove – Flange 

WARNING: Don’t use an impact wrench to take off the pinon’s nut! Remember you would be  “hammering” the bearings. 

• Bend back tab on washer that engages the Slotted Shaft Nut. 
• Using appreciate special tool, lock pinion from turning while removing the retaining nut. 
• Using appropriate special tool, remove nut. 
• Extract the flange. 

16.5.2 Remove – Seal 

Use an appropriate tool to remove  the seal

HINT: don’t install new seal at this time, wait until work covered in Final Reassembly section. 

If the Pinion Bearings are to be replaced, proceed with the next section; otherwise skip to 

Carrier Bearings – Part 2 section. 

16.5.3 Replace – Pinion Bearings 

Are you sure? A lot of set up is required if new bearings are installed. Review entire procedure and your  own capabilities before proceeding. 

16.5.3.1 Disassembly 

• While the 105 Shop Manual says to use a soft mallet, to tap the Pinion-Shaft/Gear out of the  housing, the author found this ineffectual. Also using a hammer on any bearing is a bad idea.  Stand the unit up in a press on two wood blocks and pressing out the Pinion-Shaft/Gear is a better  solution. 

CAUTION: be prepared to catch Pinion-Shaft/Gear, it will break loose suddenly. 

Even using the consistent  force of a press, the shock  wave from the sudden  release of the Pinion  Shaft/Gear from the  Pinion Bearing @ Flange shattered a 0.05 shim.

• Retrieve the cone of the Pinion Bearing @ Flange. 
• Retrieve the “Preload Shim(s)”, which can be stuck to the bearing or still on the shaft. 

CAUTION: place in separate bag marked with location of parts. It is very important to keep track  of the thickness of these original shims! 

• Pull off the Steel Sleeve (if stuck on, remove along with bearing in next step) 
• Using a bearing splitter, press off the Pinion Bearing @ Gear. 
• Retrieve the “Depth Adjustment Shim(s)”. 

CAUTION: place in separate bag marked with location of parts.  

• Carefully examine the now open interior for any debris. The differential rebuilt during the writing  of this document had a sliver of aluminum sitting in the oil drain area between the two pinion  bearings. It was probably created, and left there, when the steel sleeves for holding the bearing  cups were pressed into the aluminum housing during manufacturing. 
• Place Pinion-Shaft/Gear into plastic bag for now.

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16.5.3.2 Cup Removal 

Using appropriate special tools pull out the bearing cup for the bearing to be replaced. 

Reinstallation will be covered in Pinion-Shaft/Gear – Part 2 section.

A –Pinion Bearing @ Flange’s cup B –Pinion Bearing @ Gear’s cup	@   Flange	…. No picture available
	@ Gear

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16.6 Carrier Bearings – Part 2 

If neither Carrier Bearing was replaced, this section can be skipped. 

16.6.1 Adjust Clearance (Preload) 

HINT: Continue using the Carrier Bearing Worksheet 

PREREQUISITE: The Pinion-Shaft/Gear is not currently installed. 

• Oil both Carrier Bearing before mating cone and cup. 
• Set differential unit to main aluminum case. 
• Install LH axle tube (large flange) with nuts tightened just enough that you have an even 1 mm (0.04”)  gap between the axle flange and the aluminum case. 

WARNING: no sealant on flange 

• Reach inside and evaluate how easily you can turn the Ring Gear. 
• If you cannot turn it or only with considerable force, increase the gap and try again. 
• If you can “spin” it, reduce the gap and try again. If you are at zero gap, make the shims thicker  and start over. 
• If it turns smoothly with some resistance, you can use that gap to estimate how much thinner to  make the shims. 
• Remove LH (large flange) axle tube. 
• Adjust Carrier Bearing shims by the amount of clearance measured 

REMINDER: add / subtract equal amounts from RH and LH sides. 

• When the gap is zero and it still turns smoothy with some resistance, torque the nuts to specification (see Torque section). 
• Recheck clearance. 

If the Pinion Bearings are being replace then: 

• Remove LH axle tube again. 
• Remove Differential Assembly and store in plastic bag 
• Move on to the next section. 

Otherwise: 

• Skip to Adjusting to Specifications section.

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16.7 Pinion-Shaft/Gear – Part 2 

If the Pinion Bearings are not being replaced, skip to Adjusting to Specifications section. 

16.7.1 Install – Bearing Cups 

CAUTION: even though the ID of each Pinion Bearing is different, the OD of both cups are the same. Take  only one bearing out of its box at a time and double check you are putting the right cup in the right location! • Install the cup for the Pinion Bearing @ Gear using appropriate size bearing/seal driver, threaded rod,  and the tool that was used to extract the Pinion Bearing @ Flange cup. 

CAUTION: always verify the taper on the bearing/seal driver matches your brand of bearing. 

• CAUTION: use a thin right-angle pick to verify that the cup is fully seated into the differential  housing. 
• Install the cup for the Pinion Bearing @ Flange using same process. 
• CAUTION: verify cup is fully seated. 

NOTE: the rest of the Pinion-Shaft/Gear – Part 2 sections reverses the process listed in Alfa shop manual. To the  author it makes more sense to adjusts the “depth shim” first, since changing it will also impact the preload. While  adjusting “preload shim” has less impact “depth”. 

16.7.2 Education – Pinion Depth 

This is a good time to review General Education / Pinion Depth & Preload section. 

WARNING: There is a published specification, but it is adjusted based on the exact Pinion-Shaft/Gear &  Ring Gear in your car. This will be discussed in detail. 

WARNING: The factory tools do not use the specification directly; this will be discussed after covering  the basics. It gets complicated! 

NOTE: These specifications provide the “starting point”, the final Depth will be set based on reading the  Pinion / Ring Gear mesh pattern. This is covered in the Adjust to Specifications section later. 16.7.2.1 How to Take Depth Measurement 

Before getting into the tricky stuff, first a look at the tools and what they are going to measure.

Install tool C.6.0114  or equivalent into the  main aluminum case.  If Carrier Bearing  cups are installed, use  alternative tool (on  right)

Alternative Tool: the tapered notch  protrudes into the bearing cup.

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“Zero” depth gauge  to the reference.	6123.26.217 (Reference -1st version) + 6123.41.111 (Indicator stand)
Hold indicator stand  on end of Pinion and  then slide over the  pin until the highest  reading is obtained.  Record reading.  CAUTION: the 105  Shop Manual says  you must read gauge  to 100th of millimeter  (0.0004”)
But that reading has to be adjusted by a value determined by the exact Pinion-Shaft/Gear and the Ring  Gear installed in your car! Continue reading.

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16.7.2.2 Depth Specification – For Specific Pinion & Ring Gear

WARNING:  1st determine if a 750-series Gear portion of Pinion has 32.5 or  34.5 width.  NOTE: “A” in the illustration is measured to where shaft is  reduced in size.  NOTE: “A” in this diagram is “H” or “H1” in the next  illustrations.
Basic Specification: • Early 750: 59 mm • Afterward: 57 mm  But this will be modified  to provide a   Reference Speciation.  Then modified again to  provide a  Unit Specification.

The Reference Speciation is required because the  factory tools do not measure to the center of the  Ring Gear, but to the reference peg on tool  C.6.0114, which is 26 mm in diameter.  Therefore, you add 13 to the Unit Specification to  get the Reference Specification:  • Early 750: 72 mm  • Afterward: 70 mm	6123.26.217 (Reference -1st version)
The Reference Specification has to be customized  to the exact Pinion-Shaft/Gear and Ring Gear  installed in your differential to create the Unit  Specification.  • Based on a value etched on the Pinion. • Value is in 100th of mm

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How to interpret
Unit Specification =  Reference Specification  plus value etched on unit	(Using “Post Change” units for these examples)  • Mark is “0” then 70.00 + 0.00 = 70.00  • Mark is “+3” then 70.00 + 0.03 = 70.03  • Mark is “-2” then 70.00 – 0.02 = 69.98

16.7.3 Pinion Depth 

As discussed earlier in this document, Depth is controlled by shims. 

16.7.3.1 Depth Shim 1st Estimate 

DECISION: Use either the “Lead Shim” trick or the “Calculate Shim” method to make 1st estimate of  required shims. Instructions are found in General Education / Bearing Shims / Estimate What Is  Required section.

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16.7.3.2 Set Depth – 1st Attempt 

• Install “1st estimate” shim(s) 
• Oil shaft where bearing will go 
• Place the Pinion Bearing @ Gear’s cone on the Pinion-Shaft/Gear. 
• Fully press the bearing on to the shaft 

WARNING: do not push cone and sleeve on simultaneous, the sleeve is relatively soft metal and  will “mushroom” with the force needed to push on the cone. 

• Install the sleeve (you should be able to fully seat with finger pressure if it has not already been  mushroomed). If already mushroomed, repair it before installing. 
• Oil the bearing and cup and place Pinion Shaft/Gear in differential case 
• Install Pinion Depth Test Plate (instead of Pinion Bearing @ Flange) 
• Install flange and washer 
• Now torque the Slotted Shaft Nut (without slinger or seal) to specified value (see Torque section). • Measure the Pinion Depth. 
• Adjust reading for the “etched value”. 
• If correct, move to Education – Pinion Preload section; if not continue below. 

16.7.3.3 Set Depth – Subsequent Attempts

The last step’s reading is generally  interpreted:  • “Minus” reading:  Pinion is too close to Ring Gear • “Plus” reading:   Pinion is too far from Ring Gear. But reading has to be adjusted to  unit, see examples below.  CAUTION: total of  shim #1 + shim #2   must remain constant to not alter  Preload  Move Pinion closer to Ring Gear: • Thicker shim #2  • Thinner shim #1  Move Pinion farther from Ring  Gear:  • Thinner shim #2  • Thicker shim #1
Calculate shim  adjustment.  Examples   from 105 Shop  Manual  (Value in mm)	Note: “Calculate” column is in effect applying the Unit Specification
	Example	Gauge   Reading		Etched   Mark	Calculate	Adjust  Shim #2	Adjust   Shim #1
	1	-0.04		+ 2	-0.04 – 0.02 =	-0.06 (thinner)	+0.06
	2	+0.04		– 2	0.04 – -0.02 =	+0.06 (thicker)	-0.06
	3	-0.02		+ 4	-0.02 – 0.04 =	-0.06 (thinner)	+0.06
	4	+0.02		– 4	0.02 – -0.04 =	+0.06 (thicker)	-0.06
	5	-0.04		– 2	-0.04 – -0.02 =	-0.02 (thinner)	+0.02
	6	+0.04		+ 2	0.04 – 0.02 =	+0.02 (thicker)	-0.02
	7	-0.02		– 4	-0.02 – -0.04 =	+0.02 (thicker)	-0.02
	8	+0.02		+ 4	0.02 – 0.04 =	-0.02 (thinner)	+0.02

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HINTS:  

• When close, make shim adjustments 0.02 mm (0.001”) per attempt. 
• See Parts Interchange / Pinion Bearings section for source of shims. 
• Use provided worksheet to keep track of what you do until final successful Pinion & Ring Gear  mesh pattern is achieved 
• For subsequent attempts, measure the shim stack thickness, but record the individual shims to  make it easier to prepare for subsequent attempt. 
• Reread this before each attempt: 

Move Pinion closer to Ring Gear: use thicker shim Move Pinion farther from Ring Gear use thinner shim 

Pinion DEPTH Worksheet
Shims	Original	Lead   Trick or   Calculated Estimate	2nd Attempt	3rd Attempt	4th Attempt	5th Attempt	6th
1
2
3
4
5
Stack total
Off by

The Bad News: this may not be the last time you have to adjust the Depth. Later you will be checking  Backlash. Adjusting Backlash can require adjusting Depth, since they are interconnected. More  discussion will be added later in this document. 

16.7.4 Education – Pinion Preload 

This is a good time to review General Education / Pinion Depth & Preload section. 

Decrease Preload – use thicker shim Increase Preload – use thinner shim

16.7.4.1 How to Take Preload Measurement 

The 105 Shop Manual instruction is as follows: using the tool for leverage, rotate the Pinion twice in  clockwise direct, twice in counterclockwise direction to settle in the bearing before measurement. WARNING: Experience shows that is insufficient to get the bearing to fully settle in. Originally the  author used 2 turns and later found that the Preload was much less than what it appeared after only 2 turns.  Ten turns are used in the rest of the discussion.

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750 Factory Tool – 6123.15.006	• Install 6123.15.006  • Install 500 g weight at 250 mm position of lever (apparently weight did not come with tool from  Alfa)  • Slight finger pressure on tool should start  movement.
101/105 Factory Tool – C.5.0100	• Install C.5.0100 on yoke using two diametrically  opposite holes of the yoke.  • Secure with nuts and washers.  • Slide the weight on the RH arm to the   “101-P” position.  • Rotate the tool clockwise 10 times,   counterclockwise 10 times, and clockwise 10 times  to settle the bearing; then return the arms to  horizontal position.  • Allow the tool to find its natural position • Preload is correct when, leaving the tool arms free  in horizontal position, the weight moves down  slowly through about 30 degrees.
Torque Wrench Method  From practical level, this requires a 0-100  inch-lb. wrench. The author first used  C.5.0100 and then found 17 inch-lbs. on  my 0-100 inch-lb. wrench turned the  flange. But using a 0-600 inch-lb. wrench, no useable reading could be taken.	105 Shop Manual provides the following “revolving  torque” value:  • While rotating the flange nut with an m-kg or Inch lb. torque wrench observe a reading of 11.5-15.5  cm-kg (10 – 13.5 inch-lb.).  • Note the flange must be rotating as you take the  reading.

16.7.5 Pinion Preload (Ring Gear NOT Installed) 

As discussed earlier in this document, Depth is controlled by shims. 

16.7.5.1 Preload Shim 1st Estimate 

Make “1st estimate” of required shim(s). Instructions are in General Education / Bearing Shims /  Estimate What Is Required section.

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16.7.5.2 Set Preload 

• Install Pinion-Shaft/Gear into differential housing 
• Oil bearing cone and cup before mating 
• Lock Pinion-Shaft/Gear in place with special tool 

• Place the shim(s) determined by your 1st estimate on the Pinion Shaft/Gear. 
• Oil the Pinion Shaft/Gear where bearing will go 
• Stand the unit up in a hydraulic press (on wood strips) and then using an appropriate driver, fully  press on the Pinion Bearing @ Flange 
• Install flange and washer (without slinger or seal)  
• Using flange locking tool, torque the Slotted Shaft Nut to specified value (see Torque section). • Remove flange locking tool 
• Measure Preload as described in How to Take Preload Measurement section. 

HINT: with new bearings only, error very slightly on the side of excess Pre-load. This will allow  for very slight wear during differential break-in period. 

• Reverify Pinion Depth. 
• If correct, move to Adjust to Specifications section; otherwise, proceed with steps below. 16.7.5.3 Subsequent Attempts 

For additional adjustments change the shim stack thickness. 

HINTS:  

• When close, make shim adjustments 0.02 mm (0.001”) per attempt. 
• See Parts Interchange / Pinion Bearings section for source of shims. 
• Use provided worksheet to keep track of what you do until final successful Pinion & Ring Gear  mesh pattern is achieved 
• For subsequent attempts, measure the shim stack thickness, but record the individual shims to  make it easier to prepare for subsequent attempt. 
• Reread this before each attempt: 

Decrease Preload – use thicker shim 

Increase Preload – use thinner shim

Pinion PRELOAD Worksheet
Shims	Original	Lead   Trick or   Calculated Estimate	2nd Attempt	3rd Attempt	4th Attempt	5th Attempt	6th
1
2
3
4
5
6
Stack total
Off by

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17 Adjusting to Specifications 

17.1 The Bad News 

• Pinion Depth & Backlash are interdependent 

• Move the Pinon closer to Ring Gear   – decreases Backlash  • Move the Pinon away from Ring Gear   – increases Backlash

• Backlash & Carrier Bearing Preload are interdependent. 
• Incorrect Backlash will cause noise and premature wear on Pinion and Ring Gear. 
• Incorrect preload on Carrier Bearing can cause two problems: 
• Too little allows the carrier to move during transition from “drive” to “coast”, causing the Backlash to  constantly change. 
• Too much preload will quickly wear out bearings. 
• The 750-101 Shop Manual has instructions on how to do this, but in involves a very elaborate tool set.  Without these factory tools, the Carrier Bearings preload and the Pinon to Ring Gear backlash has to be  measured and adjusted by multiple iterations. That is what is presented below. 

17.2 Check – Total Preload 

Prerequisites: 

• Pinion Depth and Preload are both set. 
• Flange is in place (but not Slinger or Seal) and Pinion Nut is torqued to specified value. 
• Carrier Bearing shims, cones, and races are in place. 

Preliminaries

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• Oil the Carrier Bearing cones before mating with cups. 
• Carefully set Differential Assembly into aluminum housing. 
• Install LH axle tube, torquing nuts to specification (see Torque section). 

Process 

• Use the same tools and procedures found in Pinion-Shaft/Gear – Part 2 / Pinion Preload section, but make  this change: 

Tool	Procedure
Tool 6123.15.006	uses 600 g weight
Tool C.5.0100	slide weight to “101-T” position
Torque wrench	16.5 – 24.5 Kg-cm (14 – 21 inch-lb.).

• Make test at four positions on the Ring Gear: 
• Take reading, record results in worksheet 
• Rotate flange 10 turns and measure. Repeat 2 more times. 

Total Preload Worksheet
1st Result	2nd Result	3rd Result	4th Result

• Wait to adjust until after checking Backlash. 

17.3 Check – Backlash 

	C.5.0100 with indicator at 45 mm mark
REMINDER: this method is why two specifications are listed, for example 750-101: • @ Pinion Flange: 0.18 – 0.20 mm (0.007 – 0.011”)  • This provides actual backlash: 0.05 – 0.10 mm (0.002 – 0.004”)

• Inset appropriate tool into oil filler hole to lock Ring Gear from turning 
• Setup depth micrometer with indicator at the “45 mm mark” on C.5.0100 
• Turn flange back & forth and measure amount of backlash, record in chart

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• Rotate flange 10 turns and measure. Repeat 2 more times. 
• Calculate deviation from specification 

Specification:
1st Result	Dev.	+10 Result	Dev.	+20 Result	Dev.	+30 Result	Dev.

17.4 Reset Total Preload & Backlash 

Combine what you learned in the above two section. 

WARNING: as shown in chart below, if the Total Preload is OK, be sure to keep the total of RH + LH Carrier  Bearing shims constant as you adjust for Backlash. 

Total Preload			Backlash			Change	How Much
OK	Too   little	Too   much	OK	Too   little	Too   much
X				X		RH Carrier Shim – thicker  LH Carrier Shim – thinner by same  amount	See 1/3 concept below
X					X	RH Carrier Shim – thinner  LH Carrier Shim – thicker by same  amount
	X		X			Both Carrier Shims – increase same  amount	.01-.02 mm per attempt
		X	X			Both Carrier Shims – decrease same  amount
	X			X		RH Carrier Shim – thicker
	X				X	LH Carrier Shim – thicker
		X		X		LH Carrier Shim – thinner
		X			X	RH Carrier Shim – thinner

HINT: continue to update the Carrier Bearing Worksheet. 

After each change, start over at Check – Total Preload section.

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17.4.1 Change by 1/3 

How much to change shim? 

• Since actual backlash is about 1/3 of the measured backlash; try adjusting shim by 1/3 of reading plus / minus enough to keep it just under the maximum (too loose is better than too tight). 

Example	Backlash  Reading	Backlash   Specification	Difference	1/3	Bump to   near top of  spec	LH Shim  Trial   Change	RH Shim   Trial   Change
1	0.30	0.25 (max)	+ 0.05	+0.02	+0.05	Thinner by  0.07	Thicker by  0.07
2	0.08	0.15 (min)	-0.07	-0.02	-0.05	Thicker by  0.07	Thinner by  0.07
3	0.19	0.15-0.25	0	0	0	0	0

Worksheet: 

Attempt	Backlash  Reading	Backlash   Specification	Difference	1/3	Bump to   near top of  spec	LH Shim  Trial   Change	RH Shim   Trial   Change
1
2
3

When Total Preload and Backlash are properly set, move on to the next section.

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17.4.2 Check Mess Pattern (Pinion to Ring Gear) 

17.4.2.1 Education 

Generally, the position of the mesh pattern position is controlled by: 

Backlash	Vertical position (Top 🡨→ Root)
Backlash	Horizontal position difference (“drive side: toward heel with “coast side” toward toe  or visa-versa). As you correct, both will move toward the center.
Pinon Depth	Horizontal position (Heel 🡨→ Toe)

The mesh pattern on the “drive side” is more critical than the “coast side”. But the “Coast” pattern can  never go off the end of the Toe, Heel, or Top  

Backlash can be altered by: 

• changing Pinion Depth shims 
• moving a Carrier Bearing shim from one Carrier Bearing to the other Carrier Bearing (RH 🡨→ LH). 

Pinion Depth is altered by changing Pinion Depth shims. 

As you make the above alterations, keep this in mind: 

• while Pinion Depth was originally set to a very specific value, based on mesh pattern it may be  moved off that specific value as needed. 
• Backlash must always remain within the specification range. 

17.4.2.2 Procedure 

After the Total Preload and Backlash are correct, then review the gear mesh. 

• Remove the LH axle tube (large flange). 
• Lift out the differential, carefully paint both the “drive side” and “coast side” of all the Ring Gear  teeth with “gear marking compound”. 

• Assemble the unit, including LH axle tube. 
• Torque LH axle tube nuts (see Torque section). 
• Insert the RH axle into the differential. 
• While an assistant puts some resistance to the RH axle, rotate the driveshaft flange at least 40 turns  clockwise and 40 turns counterclockwise.

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• Disassemble and review the mesh pattern: 
• Against the photo you took of the mesh pattern before any bearing changes. 
• Against the discussion below 
• Adjusting as prescribed. 

17.4.2.3 Mesh Pattern Review 

The following chart does not contain all possible combinations, but those commonly encountered.

Drive Side Coast Side
Mesh pattern is near Problem
Toe	Center	Heel Toe	Center	Heel
	X		X	No problem – perfect
	X			XAs long as Coast side does not go off the  end of Heel, it is acceptable
X		X		Backlash too tight
		X		X Backlash too loose
X				X Pinion too close to Ring Gear
		X X		Pinion too far from Ring Gear
Top   (Face)	Center	Root   Top   (Flank)  (Face)	Center		Root   (Flank)
	X		X		No problem – perfect
X		X			Backlash too loose
		X			X Backlash too tight

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750-101 Differential Page 62 Rebuilding Differential 

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750-101 Differential Page 63 Rebuilding Differential 

17.4.3 Examples 

The following photos are from the project used for this document. 

1st Pattern Review

An experienced differential rebuilder (not the author) provided conclusion after reviewing photos: • The Pinion is a little too close to the Ring Gear (use a 0.002-0.003” thinner Depth Shim and Preload  Shim 

• The Backlash is a bit loose. 

2nd Pattern Review  • Depth shim was reduced by 0.01 mm.  • Since the measured Backlash was near the bottom (tight) side of the Alfa specification the author  decided not to change it.

It was now found that the Backlash was looser than before. It was now above the allowed range at  0.012”, 0.012”, 0.012”, 0.015” in the four test locations.

The experienced differential rebuilder after review of 2nd photos: 

• Reduce Backlash by moving 0.001-0.002” shim from RH to LH Carrier Below are the results from  moving a 0.01 mm shim from the RH Carrier Bearing to the LH Carrier Bearing.

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750-101 Differential Page 64 Rebuilding Differential 

3rd & Final Pattern Review

It was now found that the Backlash was 0.006”, 0.009”, 0.006”, 0.009”, 0.006”

The experienced differential rebuilder after review of 2nd photos: 

• This is probably as close as you can get to being correct. 

17.5 Decision 

• Does “gear marking compound” confirm Pinion Depth is correct? 
• Does “gear marking compound” confirm Backlash results found in previous step?

• Total Preload  • Backlash  • Mess	correct	proceed to	Final Reassembly section.
Backlash	incorrect	return to and repeat	Reset Total Preload & Backlash section
Pinion Depth	incorrect	return to and repeat	Pinion-Shaft/Gear – Part 2 / Pinion Depth / Set  Depth – Subsequent Attempt section.

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750-101 Differential Page 65 Final Reassembly 

18 Final Reassembly 

18.1 Install – Pinion Slinger & Seal 

RECOMMENDATION: use a double lip seal instead of the original single lip seal. Both numbers in Parts  Interchange section. 

• Install Slinger – but which way? See illustration below. 

• Smear light coat of silicon sealer on edge housing where seal will go. Probably not needed if seal is of type  with complete rubber exterior. 
• Using appropriate bearing/seal driver, pound in seal. 

18.2 Flange 

This is referring to the flange that couples to the driveshaft. Examine the seal surface on the flange. • If there is enough wear that you can feel a groove with your finger nail; install a “Speedi-sleeve”. 

If no Speedi-sleeve is  available to match the  exact diameter of the   flange, you will need to  have a machinist reduce  the flange diameter to  match the available   sleeve.  A lath will also be need  to remove the Speedi sleeve lip, after   installation.

• Fill seal contact area with Molykote before installing flange. 
• Apply Loctite 648 sleeve retainer to flange splines  

This is based on 1974/12 Service Bulletin specified Loctite 27 Sleeve Retainer (obsolete product) on the  splines for 105 & 115 cars. 

• Install flange. 
• Install tab washer, with tab into hole in flange, and Slotted Shaft Nut 
• Torque nut to specified value, starting near bottom of range and increase as needed to align washer tab with a  Slotted Shaft Nut’s slot. 
• Bend over one tab on washer to lock Slotted Shaft Nut

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750-101 Differential Page 66 Final Reassembly 

18.3 Differential 

• Clean Gear Compound off the Pinion and Ring Gear with brake cleaning spray and let dry. • Oil bearings with appropriate differential oil 
• Place differential into aluminum case 

18.4 Axle Tubes 

• Prevent future leaks by preparing differential and LH axle tube contact areas: 

• Clean with Acetone. 
• Treat with Loctite “Klean ‘N Prime”, let dry 5 minutes 
• Applying a thin layer of Loctite 515 to the area prepared area of the LH axle tube 

CAUTION: do not put Loctite on any other surface because doing so would change the Carrier  Bearing Preload and the Backlash. 

• Install LH axle tube onto differential. 
• Install the lock “bands” as shown in illustration below 

• Install and torque retaining nuts (see Torque section). 
• Bend over locking “bands”.

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750-101 Differential Page 67 Final Reassembly 

• Prevent future leaks by preparing differential and RH axle tube using same process as LH axle tube. • Install RH axle tube onto differential. 
• Install the lock “bands” as shown in illustration above 
• Install the brass brake line figure as shown in the illustration below. 

• Install and torque retaining nuts. 
• Bend over locking “bands”. 

18.4.1 Brake Backing Plates & Axles 

For installation, refer to earlier Axles section. 

18.5 ID Decal 

The following has been provided by others. 

101-1600 had the yellow  lubrication sticker shown  below on the differential

18.6 Brake Pipes

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750-101 Differential Page 68 Final Reassembly 

19 Trailing Arms & Reaction Triangle 

19.1 Tailing Arms 

See separate document titled “Trailing Arms” for how to reinforce the weak attachment points 

19.2 Reaction Triangle Ball Joint 

…. Maybe a future section, but here are a couple of thoughts ……… 

CAUTION: Don’t try to pry up on retaining ring near the “prong”. Start at opposite end and “unwind” the retaining  ring. 

CAUTION: Measure and record height of cup above Reaction Triangle before unscrewing cup. This will allow you  to put it back at original torque setting. 

20 Break-in Procedure 

The following procedure is generally accepted for breaking in a new gear set. Drive below 60 m.p.h., approximately 15  to 20 miles, then stop and let the differential cool. Avoid abusive situations for the next 100 miles or so, and then have  at it. If you take it easy on a new ring and pinion, and keep it full of high-quality oil, it will last a lot longer. .

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750-101 Differential Page 69 Modified 750 & 101 Options 

21 Modified 750 & 101 Options 

This section was provided by others and not personally verified by the author. 

21.1.1 Suggestions for Modified Cars 

Alfa, in their infinite wisdom, chose the correct rear-end ratios to best suit the car-gearbox-engine  configuration for NORMAL USE. In other words: 

• 750-101 1300 with Solex [Normale] and 4-speed works best with 5:12.  
• 750-101 1300 Veloce with 4-speed works best with 4:10 
• 1600 Normale with 5-speed works best with 5:12 or maybe a 4:56. 

Once you start upgrading the engine, the 5:12 is a real dog and you’ll run out of gears quickly. Any real  upgrade, such as Webers, 1750 pistons etc. will require you to change the rear end to a 4:56 and 5-speed.  Otherwise, you’ll go crazy by running out of revs.  

You should find 5:12 at giveaway prices, 4:56 more difficult to come by, and 4:10 almost impossible to find.  I put 1750 pistons in a 1600 Spider Normale, with Webers of course, and could not drive the car until I found  a 4:56 rear 

21.1.2 Mixing 750 & 101 Parts 

• 750 axle has smaller bearings for differential and coarse splines on the half shafts, so you can’t mix  parts. 
• If you want to use complete 101 axle and your 750 brake backing plates, you will need to make the  center holes in the back plate larger to fit over the half shaft bearings. 

21.1.3 Replace 750/101 with 115 

Pro 

• Buying used is cheaper than rebuilding if you cannot do it yourself 
• Limited-slip 

Con 

• Mounting modifications required 
• The spring perches are removed from the old axle tubes and welded to the new axle. 
• A trunnion socket can be welded onto the axle if you keep the old ball joint style trunnion. • If you want a 5.12 ratio your choices are an old axle or a GTA axle. But if you want a 4.56 or 4.10  ratio a 115 axle is a great upgrade to our cars. 

21.1.4 115 Differential with 101-1600 Axle Tubes 

The 1300 axle will not allow for this modification  

Pro 

• Buying used is cheaper than rebuilding if you cannot do it yourself 
• The axle tubes will bolt directly to the 115-series center section 
• Once together it is very difficult to tell from the original. 
• Norman racing in Berkeley CA does both of these modifications. 

Con 

• Mounting modifications required 
• The Carrier Bearing on the LH side must be changed, so must be able to reset clearances.

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750-101 Differential Page 70 Hardware 

22 Hardware 

This list only covers the 101-1300 differential worked on during development of this document 

Alfa #	Purpose	Description	Count	Size	Pitch	Length	Finish
1365.32.131	Fix axle retainer  to axle tube	Stud  (different threads each end)	8	10	1.0  1.25	Total -53 1.0 –24  1.25 – 14	Black
2120.20046		Nut	8	10	1.0	N/A	Black
2120.20249		Pal nut	8	10	1.0	N/A	Black
1365.32.023	Fix bearing to  axle	Slotted Shaft Nut	2	43?	?	N/A	Black
1365.32.025 (607.07219)		Multi tab washer	2	43?		N/A	Black
2100.08975	Fix axle tube to  center casting	Stud  (different threads each end)	7	8	1.0  1.25	32	Black
2100.08979		Stud  (different threads each end)	1	8	1.0  1.25	41	Black
21202.16425	Pinion	Slotted Shaft Nut  (wrench 6121.20.035)	1	20	1.0	N/A	Black
1365.32.055		Tab washer (6 external tabs  1 bend up to lock nut, 1  bend down)	1	20	N/A	N/A	Black
Pre-modification
1365.21.010	Fix Ring Gear	Bolt	8	8	1.0	23.5	Black
2140.17174		Tab washer	8	8.4	N/A	N/A	Black
Post-modification
1356.31.006 Footnote 8	Fix Ring Gear	Bolt  (see below for source)	8	9	1.0	Footnote  9	Black
2140.17175		Tab washer	8	9.5	N/A	N/A	Black

22.1 9 x 1.0 Bolts 

• Salvage from a 105 series differential, these are bolt 102.00.17.216.00.  
• At least in 2021, source from www.heinbrand.com 

NOTE: these are flange bolt with serrations. They are grade 12.9. But they are 26 mm long, so to use on a  Giulietta or 101 Giulia differential you must accommodate the extra length. 

22.2 Multi-tooth Tab Washer 

The following has been provided by others and not personally verified by the author. 

Possible source for 1365.32.055 tab washer is SKF 20 mm tab washer “MB4”

8It is recommended that the stronger bolt be used. 

9 Spare Parts lists this bolt as 9 x 1.0 x 22.5, but what was found was 9 x 1.0 x 16.75 mm.

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750-101 Differential Page 71 Hardware 

22.3 Bearing Shims 

Original			Source
Bearing	ID x OD	Nominal	Thickness	Vendor
Pinion @ flange	25.53 x 36.05	25 x 36	Available:  0.1, 0.2, 0.3, 0.5,  1.0, 1.2, 1.5, 2.0	Metric & Multi-standard #988:  25 x 36 + thickness
			Available:  0.1, 0.2, 0.3, 0.5,  1.0, 1.5, 2.0	McMaster-Carr – search on “Ring  Shims”, then 25 mm ID
Pinion @ gear	31.58 x 41.75	32 x 42  (1 ¼ x 1 ¾ “)	Available:  0.001” – ¼”	McMaster-Carr – search on “Ring  Shims”, then 1 ¼” ID
			Available:  0.1, 0.2, 0.3, 0.5,  1.0, 1.2, 1.5, 2.0	Metric & Multi-standard #988:  32 x 45 + thickness
Carrier – OEM  – under cup	58.88 x 71.51	58 x 71	(4) 0.07	www.drivetrainamerica.com  701121X Dana 35 Pinion Shim Kit 60.35 x 70.81  (#) = count of item in set:
			(2) 0.12
			(2) 0.25
			(2) 0.75
Carrier –  alternative   – under cone	35 x 52	35 x 45   (1 ¼ x 1 7/8 “)	Use same 1 ¼” ID shims as listed under Pinion @ gear
			Set of 19:  0.001 – 0.125”	Precision Brand #25261, 1 3/8“ ID  See section below for details
			Available:  0.1, 0.2, 0.3, 0.5,  1.0, 1.2, 1.5, 2.0	Metric & Multi-standard #988:  35 x 45 + thickness

22.3.1 McMaster-Carr – Precision Brand 

At least in July 2021, McMaster-Carr shims are Precision Brand, which is also available from other vendors. 22.3.1.1 Precision Brand – Set #25261  

• This is an assortment of 1 3/8 x 1 7/8” (35 x 45 mm) 
• Also available as McMaster-Carr #3088A939 
• Set has one shim each in the following thicknesses:

Inch	mm	Measured
0.001	0.025	0.02
0.0015	0.038	0.03
0.002	0.051	0.04
0.003	0.076	0.06
0.004	0.102	0.09
0.005	0.127	0.12
0.006	0.152	0.14
0.007	0.178	0.17
0.008	0.203	0.20
0.010	0.254	0.24
0.012	0.305	0.29
0.015	0.381	0.38
0.020	0.508	0.50
0.025	0.635	0.62
0.031	0.787	0.76
0.047	1.194	1.22
0.062	1.575	1.55
0.093	2.362	2.30
0.125	3.175	3.17 had ridge

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750-101 Differential Page 72 Hardware 

23 Torque  

• The 750-101 Shop Manual does not provide any information. 
• Giulia Spider Veloce Giulia Sprint Speciale Technical Characteristics and Principal Inspection Specifications provides a good list. 
• The 105 Shop Manual provides values.  
• CAUTION: the 101-1600 tailing arm torque values may be incorrect as they are the same as the 105, which  have larger bolts (12 vs. 16). The listed value is more than the generic torque for a 12 mm bolt (61 ft-lb). • NOTE: all are listed as “dry”  

Item	750-101  Fastener #	Size	105   Fastener #	Size	101-1600 Torque Kg-m. lb.-ft.		105 Torque  Kg-m. lb.-ft.
Axle retainer to  axle tube – @  brake backing  plate	1365.32.131	10 x 1.0			4.8-5.5	34.8-39.7
			2100.08477	10 x 1.0			4.8–5.5	34.8–32.7
Fix axle tube to  center casting	2100.08975 2100.08979	8	2100.08997  2100.08679	8		Footnote  10
Pinion Slotted  Shaft Nut	2120.16425	20 x 1.0	2120.16425	20 x 1.0	8-14	58-101.2	8-14	58-101
Ring Gear	1365.31.010	8 x 1.0				Footnote  11
	1256.31.006	9 x 1.0   Footnote 12	102.00.17.216.00	9 x 1.0	4.5-5.0	32.6-36.1	4.5-5.0  Footnote 13	32.6-36.1
Driveshaft to   pinion flange	2100.20042	8 x 1.0	2100.20042	8 x 1.0	4.5-5.5	32.6-39.7	3.5–4.0	25.3–28.9
Tailing arm to  chassis	1356.48.065	12 x 1.5	105.00.25.326.00	16 x 1.5	10-11.5	72-83	10-11.5	72-97
Trailing arm to  axle tube	1365.48.066	12 x 1.5	105.00.25.319.00	16 x 1.5	11.5-13	83-94	11.5-13	83-94
Reaction   triangle to   chassis	1356.48.065	12 x 1.5			4.8-5.5	34.8-39.7
Reaction   triangle to   differential	1365.45.412				11-15	79.6-  108.5

10 Generic torque value for 8 x 1.0 bolt is 18 lb.-ft. (216 lb.-inch) 

11 Generic torque value for 8 x 1.0 bolt is 18 lb.-ft. 

12 Spare Parts lists this bolt as 9 x 1.0 x 22.5, but what was found was 9 x 1.0 x 17. 

13 Shop manual list torque as “dry” while others recommend using Loctite Red, because loose bolts are a known problem.

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750-115 Differential Page 73 Factory Tool Bulletins 

24 Tool Bulletins

WARNING: Information Sheet 17.69.4.1 (1969 /10/20) instructed service departments to alter reference setting tool  C.6.0101; as Alfa thought some uses were obsolete (they never planned on us still working a Giulietta 50 years later).

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750-115 Differential Page 74 Factory Tool Bulletins 

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750-115 Differential Page 75 Factory Tool Bulletins 

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750-115 Differential Page 76 Factory Tool Bulletins 

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750-115 Differential Page 77 Factory Tool Bulletins 

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750-115 Differential Page 78 Factory Tool Bulletins 

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750-115 Differential Page 79 Factory Tool Bulletins 

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750-115 Differential Page 80 Special Tools – Construction Diagrams 

25 Special Tools – Construction 

25.1 Pinion Bearings Cups – Remove / Install

A – outer bearing cup,  B – inner bearing cup D  – cup installer	A – remove outer bearing cup
B – remove inner bearing cup	These pieces are all made of quality steel, at least 4 mm thick.

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