limited slip differential oil

[PatinaBeforePolish]

Following Mike Miller's (RIP) lifetime maintenance schedule I'm using Redline 75W-90 synthetic gear oil in my sideloader limited slip diff. I've noticed a bit of binding in sharp turns and would like to hear if anyone uses a different gear oil that could prevent this. I believe it's an older differential as it uses a 70mm bolt and nut on the diff flange rather than the flange being threaded so it could be just a sign of clutch wear. Thoughts? Thanks!

[Mike W.]

No personal experience.

I have heard things can get cranky if you don't run a an oil which claims to be LSD compatible. Nothing like failure, but letting you know it's not happy.

What exactly a LSD compatible oil is, I have no idea. Except for the claims on the bottle.

[John in the Glade]

When I acquired my latest E12, the PO said he had the whole car serviced a year before. That included the rear differential. Unfortunately the rear started to make growling noises since then. It was fine for the first 20-30 minutes before a the ghosts started moaning. He didn’t know what fluid was used, presumed it was generic 75W90.

I know our era rear gears are hypoid geometry, and therefore require HYPOID GEAR OIL. I think I got Chevron(?) Hypoid 75W90 from a local parts shop, drove the car a bit to warm it up and crawled underneath to drain and refill. That was 20 years ago, but the rear has run quietly ever since.

Yeah, I know, . . . my differential is a standard open, where yours is LSD. But I’d presume the engineers at BMW who did OD hypoid gears would carry on that design with the LS version. (Makes sense to keep it the same, if only to use the same fluids and reduce confusion).

Last I checked, Redline doesn’t have a hypoid gear product. If it were ME, I’d drain and fill with what BMW recommends.

Good luck! Keep us informed.

[PatinaBeforePolish]

Thank you @ John in the Glade. So I referenced what I should have in the first place- the factory repair manual. It says to use a name brand SAE 90 hypoid gear oil and nothing about additives for limited slip. My next step will be to try that without an additive, then with an additive if it still binds. The on-throttle whining could also be the pinion gear bearing which is pretty common but somewhat easy to replace. [url]/url]

[PatinaBeforePolish]

I replaced the Redline 75/90 synthetic with LiquiMoly 85/90 hypoid gear oil, added Redline limited slip friction modifier which seems to have resolved the chatter in tight turns without reducing the limited slip effect. I still have a bit of on-throttle whine but it's now at much higher speeds. I'll see how it goes after a few thousand miles but good for now.