Totally unmarked diff

[stillkotd]

I finally decided to crawl under the rear of my '89 325i to check the diff ratio... and there are no numbers on it.

I thought maybe it was just dirty, so I cleaned it up really well, and there are no markings on it whatsoever. I heard somewhere that sometimes there's a metal tag with numbers on that too, but I can't find one on mine.

Is there some other way to identify what ratio diff I have, besides taking it off and opening it? Also, I know there was a chart on here with all the stock ratios for e30s and which ones came with an lsd. Searched but couldn't find it, anyone have a link to that thread?

[jlevie]

If your car has an automatic transmission it would have come with a 4.10. If a manual transmission it would have come with a 3.73. Either differential could be open or a limited slip.

You can find out what the ratio is by counting turns of the drive shaft and wheels. A 4.10 will yield 41 turns of the drive shaft for ten turns of the wheels. A 3.73 will be 41 turns of the drive shaft for 11 turns of the wheels.

[stillkotd]

Hmm... any way to tell if it's limited slip? That's actually why I wanted to check the numbers in the first place, to see if there was an "S" stamped on it.

[Blackangusinc]

Hmm... any way to tell if it's limited slip? That's actually why I wanted to check the numbers in the first place, to see if there was an "S" stamped on it.

Pull the rear end off the ground and spin one wheel. If the opposite wheel spins in the same direction it's a limited slip.

[Jaxx_]

the tag is on the side of the diff, attached to one of the diff cover bolts. it's closest to the right rear, but one of the higher bolts on the diff. probably about the 2 O clock position if you were looking at the diff's drain plugs. It's roughly 1cm wide and 6cm tall. (from my memory)

[AldcE30]

good to know