R M diffs. different?

[claylake]

In an attempt to lower my final drive ratio from 3:91 to 3:46 I purchased a 3:46 from the salvage yard replaced the seals, cleaned, and painted it only to discover my diff. appears to be 2" longer. Are our diffs. unique to the M's? Anybody need a 3:46?

[ddstl]

M5 and M535i came with bigger diffs. You should be able to put your 3.46 diff in without any trouble(I just recently removed a 3.07 big-case diff and replaced it with a 3.46 from an E23). The diffs are bigger, but the mounting points, and the relationship between both diffs and the driveshaft, is the same. You will likely need to do the usual swapping of shaft flanges in favor of the ones used with the 3.91. You may also need a rear cover depending on where the diff mount bolt sits in relation to the cover(big case diff covers do not swap with medium case diffs)

I have a 3.07LS big-case diff that I am not using if you are interested in trading for the 3.46LS.

[claylake]

Thanks. I was worried there was no direct swap for a taller gear. Perhaps I got a small case diff. from the yard. Mine is an M6 but should be same as M5. I am going back to the junk yard this weekend and try to swap. Thanks for the offer. The 3.07 might be too tall. In the testing phase right now to see what works best with my turbo.