What's the diff in shim thickness?

[Dug Nichols]

I've got a leaking differential in my '73. Again. :(  I removed it 2 years ago and re-sealed both axles as well as bearing, re-sealed the rear. Alas, the driver side is still leaking and appears to be both the output bearing housing and the axle shaft seal. 

 

I am fairly certain the diff is a replacement from a '76 e21 -- a few pix posted and would appreciate confirmation of this.

 

In looking up replacement parts, I see at least five different thickness shims listed in realoem. Any advice on how to decide which thickness to purchase?

 

[Conserv]

I can’t help you solve your shim thickness issue. But I can confirm (or deny) your general conclusion about the differential’s origins!

 

The housing was cast December 1, 1976 (“01M76” cast into the top rear of the housing), the differential was assembled January 1977 (“1” over “7”, stamped into the left front flank of the housing), and the rear cover was cast September 1976 (9? nubs surrounding “76”). The original ratio was 3.64 (“40” / “11”, stamped into the left front flank of the housing).

 

But that looks like an ‘02 rear cover, not an e21 cover. And it post-dates the end of 2002 production in July 1976. So it appears to be a replacement part. Yes, of course, the rear cover may well have been transferred from an ‘02 to an e21 differential. But when all the dates are relatively close — September 1976 through January 1977 — my first guess is that this is a replacement differential for an ‘02. Notice also how the stub-axle flanges stand away from the four-bolt side covers. Below is a 1978 differential, from an e21, with the same four-bolt side covers: but note how close the flanges sit to the side covers. The differential could have also started life in a 1977 e21 (produced August 1976 through August 1977), but then you must explain why it happens to have an ‘02 replacement rear cover, a relatively rare item. And there must have been some modifications to move those flanges outward.

 

Sorry to distract from your real needs, but I love a well-dated piece of machinery! ?

 

Regards,

 

Steve

 

[Schnellvintage]

If you have any grooves or galling on the output shaft where the seal rides, that could be the issue.  Also the shims go first against the bearing housing then the o-ring seal.  The shims support the bearing and backlash clearance, as long as all four bolts (each side) are at the same torque spec.  

FWIW

[AceAndrew]

Why do you think you need new shims?  They are not a wear item.

[Dug Nichols]

Ooooo, good deets! Thanks. 

 

When I did the rebuild two years ago I accidentally put a slight bend in the shim. I figured it would press out just fine, but am slightly suspicious of this and figured it'd be a cheap part while I have it out and open again. Just not sure on appropriate thickness..

[2002iii]

First off shims have nothing to do with sealing. They are used to align the ring gear with the pinion gear. If not done properly the diff will usually make noise and wear prematurely.

 

If you want to replace the bent shim you need to measure its thickness to determine which one you need to buy.

 

Like @Schnellvintagesaid you should check the sealing surfaces 

[TobyB]

Answer to post title- thikness.

 

Did you replace the o- rings in the inset groove inside the side covers?

 

They seal the shims so oil can't get out that way.

 

If you didn't have any o- rings and can't find any,

 

o- ring- in- a- tube will work, but in this instance you 

have to be really careful to only use the barest minimum the 

groove will take.  Too much will squooge in between the shims,

and then you'll have... well, eventually, other problems.

 

t

do nawt seek to replace the shims.

[Dug Nichols]

yeah, I did replace the o-rings. my refresh two years ago included:

• rubber o-rings (shows as #10)
• roller bearings (#8)
• shaft seal (#4)
• rear cover gasket

I was def disappointed that it still leaked. Scratching my head a bit for sure, as I thought I did everything by the book correctly. Oh well, as soon as the spring melt water dries out a bit I'll be taking the diff out again and concentrating on the driver side!

 

Thanks for all the tips.

[Schnellvintage]

Do you have a Long Neck Diff??  Those have the aluminum sides.  They can also leak around the bolts in the side cover.  I use a little Dirko (or other sealant) on the threads when installing.  

 

 

 

 

Edited March 5, 2021 by Schnellvintage
typo

[Dug Nichols]

12 hours ago, Schnellvintage said:

Do you have a Long Neck Diff??  Those have the aluminum sides.  They can also leak around the bolts in the side cover.  I use a little Dirko (or other sealant) on the threads when installing.  

 

 

 

 

Oh, nope! It's a shortneck (not as pictured from realoem diagram)