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Diff Leak


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The car is almost done with its mechanical restoration and it went on its first 100 mile trip. Its been sitting a week after the trip and i have a nice hand size puddle on the floor under the diff. Its coming from the front of the Diff.

I did some searching on the forum and it seems a lot of people just live with a leaking diff, but this seems like quite a good leak. I am running fresh Redline 75w90 in the diff. Could changing to a different fluid slow the leak at all?

I guess i can always buy a refurbed unit from Aardvarc since what im reading online is that refurbishing the diff is not a home job.


1976 BMW 2002 Chamonix. My first love.

1972 BMW 2002tii Polaris. My new side piece.

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If it is not making noise you should try changing the Pinion Seal. It is more dificult that just taking the nut off, pulling the flange, replace the seal and re assemble because you have to watch the preload of the pinion bearings.

This is much easier to do on the workbench so I recomend you pull the diff out of the car, but it can be done with the diff in place.

You need to mark the position of the input flange and the nut in relation to the pinion. My recomendation is a punch mark on each to line them up (paint gets wiped off while you are cleaning) Remove the lock plate and again check that you have marks on the pinion, the nut and the flange that all line up. Remove the nut, you will need a thin wall 30mm socket. The flange should pull off straight off the splines, might take a puller! you can now pry the old seal out and install the new seal. Make sure it is square in the bore! Put a little oil on the seal and reinstall the flange, make sure the mark you made on the pinion and flange line up!!! Now you can install the nut, I recomend some red loctite just for safety. Tighten until the mark on the nut lines back up with the marks you made on the pinion and flange DO NOT TIGHTEN IT ANY MORE OR YOU WILL OVERLOAD THE BEARINGS AND TRASH THEM!! Now install a NEW lock plate and put the diff back in the car (don't forget to refill with oil)

1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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if your going to switch lubricant

go to the Original recommended oil:

SAE80w90 GL4

(same oil for your steering gear box)

PENNZOIL # 21176


replacing the front pinion seal is:


'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

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