What's the diff?

[billmcdaniel5]

The differential in my 1989 535M is giving warning its on its last legs. Would like to intervene before it dies. What are my options and where do I find a used one? Have been perfectly happy with the stock unit so I don’t have to have some exotic gearing or LSD.

Thanks,

Bill Mc D

[gale]

Stock, yours most likely has a 3.46, could be LSD or could be open. They are pretty easy to find used, you could take your chances on many used ones for the same cost of having yours rebuilt. As for changing ratios, an e32 3.64 would be nice. A 3.91 wouldn't be out of line but anything higher than that is getting extreme. An e34 3.73 will also fit. For compatibility, the most you'd have to do is maybe swap the axle hubs (super easy) and perhaps swap the input hub, be careful not to preload it too tight, 125 ft-lbs w/Loktite is a pretty safe torque.

Run full synthetic gear oil, spec GL-5. 75W90 is usually sufficient. Maybe add 4-6 oz. of LSD additive but most synthetics won't need it.

[Rigmaster]

Agree with what Gale said, EXCEPT the part about the 3.46 E34 diff being pretty easy to find. They only came in the 535iM so they are "uncommon" if not "rare".... Seems that the 3.46 ratio is very popular for the E36 guys too- so many of the E34 3.46 diffs seem to be getting pulled apart and the gears used for other applications.



Anyway, you should not have too much trouble finding a suitable diff for a reasonable price- I'd say $250-500 delivered depending on ratio, LSD or open, mileage, etc.

As Gale mentioned, depending on the vehicle your "new" diff comes from, you might have to swap flanges. Side flanges are a snap- they simply pop out with a screwdriver and pop back in by hand. The front (input) flange is a different matter- it needs to be carefully torqued to spec and you are supposed to use a new crush washer each time you change it. Since your car is a manual E34, you would be smart to find a diff from another manual E34 OR any E32 6 cyl car since these should have the correct size input flange that will bolt right into your car.


I have a couple of E34/E32 LSD's for sale- 3.23, 3.64, 3.91 and 4.27.

Let me know if interested in one of these.



thanks!

Bret.