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What differential is this?

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Hooray! I got the differential out of my '73 that I'm slowly working on sorting out and getting running after many years stored in a garage. It was demonstrating leaks on one of the output shafts and at the rear cover.  After getting it out, I started cleaning about a 1/4" of sludge all over it, especially near the rear and one side. As it started cleaning up, I noticed that there's two yellow dots painted on the top of the diff. Hmmm, me thinks this may not be the original differential for this car. (I bought from original owner but he had spotty records).

 

I got the cover off and see there's no gasket at all! Well there's one obvious place I'll be able to improve it.

 

Then, turning my attention to the output flanges I see that these flanges do not match the shop manual or realoem diagrams. There's no center bolt holding the flanges in. Curious. And, uh oh, now I'm stuck. 

 

After all this fun, I'm left with two questions I'm hoping the hive can help me answer:

1. What is this differential?

It is stamped 01M76 on the outside. On the inside of the rear cover is 1.204.113 225

 

2. How do I access the shaft seals?

 

 

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it is a '76 diff. the flanges are held on by a circlip at the end of the flange stem on the inside of the diff. there is a single hole in the clip, pull it off with a hook tool

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Count the gear teeth if it's a 76 theirs a good chance it's a 3.90 diff, by the way there is a gasket on the rear cover.

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(edited)

The housing was cast December 1, 1976 (“01M76”).  The rear cover was cast October 1976 (ten nubs surrounding “76”).

 

Both of these dates are after the end of 2002 production, but it could be a replacement part.

 

The original number of pinion and ring gear teeth are likely stamped into the left front side of the differential, just above the assembly month and year. Below is the original differential from my ‘76: it shows a ratio of 3.90 (“10   39”) and the differential was assembled April 1976 (“4” over “6”).

 

The housing on my ‘76’s 3.90 was cast March 24, 1976 (“24376”), as shown in the second photo.

 

Regards,

 

Steve

 

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Edited by Conserv

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1 hour ago, Conserv said:

The housing was cast December 1, 1976 (“01M76”).  The rear cover was cast October 1976 (ten nubs surrounding “76”).

 

Both of these dates are after the end of 2002 production...

 

Regards,

 

Steve

 

...which probably means it's a 320 diff.

 

If you don't find c- clips on the inside (I never have) then pull- hard- and see if the flanges pop out.

t

 

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Also, the photo you show with the shop manual picture is of a long-neck diff, which is a whole different kettle 'o fish from a shortneck, which is what your car has...

 

mike

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(edited)
3 hours ago, TobyB said:

 

...which probably means it's a 320 diff....

 

 

My starting point, Toby, was.... this is a 320i (e21) differential. But that 2002 rear cover, similarly-dated to the differential housing, threw a wrench into the works....

 

The differential and the rear cover could certainly have been “married” anytime after they were produced. But it’s worth noting that the casting dates are both (a.) close and (b.) post-2002, which suggests both components could have been together since new. How often do you see 2002 rear covers with October 1976 casting dates? Not often is my guess. I think...

 

Best regards,

 

Steve

 

Edited by Conserv

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41 minutes ago, Conserv said:

 How often do you see 2002 rear covers with October 1976 casting dates? Not often is my guess. I think...

 

In Europe pretty often but that would be 1502 with 4,11:1.

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Thanks for the great insights everyone!

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(edited)
9 hours ago, Conserv said:

 

My starting point, Toby, was.... this is a 320i (e21) differential. But that 2002 rear cover, similarly-dated to the differential housing, threw a wrench into the works....

 

The differential and the rear cover could certainly have been “married” anytime after they were produced. But it’s worth noting that the casting dates are both (a.) close and (b.) post-2002, which suggests both components could have been together since new. How often do you see 2002 rear covers with October 1976 casting dates? Not often is my guess. I think...

 

Best regards,

 

Steve

 

 

You know, I took the OP's 'no seal' at face value.  And figured they'd been apart

 

But- there's an obvious gasket on the cover, and I agree, with those date CASTINGS,

if that diff originally came in a car, it came in Tommy's 1502.  And it likely came with that 

cover, thus making it far less likely to be originally a 320 diff.

 

Of course by this point in production, the only differences 

between 2002 and 320 are the length of the output flanges

and the rear cover, so for BMW to have made a significant number of spares,

crated them, Stuck them in Der Vherehaus,

 and then sent them out later, as needed, is a pretty likely scenario.

Just like they did a couple of M10 spare head casting runs, the last of which was

just after global M10 production stopped for good.

 

t

agrees with Steve, now.

Edited by TobyB
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(edited)
8 hours ago, Tommy said:

 

In Europe pretty often but that would be 1502 with 4,11:1.

 

and 1502 were made until the middle of 1977, just saying 🙂

Edited by NickVyse

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(edited)
14 hours ago, NickVyse said:

 

and 1502 were made until the middle of 1977, just saying 🙂

 

Given, however, the number of 1502’s in the States — a handful — I’m guessing this is not a 4.11, but is a 3.90 or a 3.64, installed by a dealer after the original (ca. 1973) differential failed. That failure could have occurred any time after 1976. I say “dealer” only because dealers are more likely to use factory-new parts whereas independent shops might source a used unit for a similar need.

 

Regards,

 

Steve

 

Edited by Conserv

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3.90 short neck.

Stamped numbers indicate this: 39 / 10 = 3.90.

 

Slavs

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3 hours ago, Slavs said:

3.90 short neck.

Stamped numbers indicate this: 39 / 10 = 3.90.

 

Slavs

 

Slavs,

 

We have not yet seen the stampings on the original poster’s differential.  I posted a photo of my ‘76’s differential so he’d know where to look on his differential.

 

Regards,

 

Steve

 

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Plot is thickening....

I'll post a photo of the stamps when I get home tonight.

 

(also sorry my bad on the gasket cover)

 

 

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