About diffs....I swapped mine out for a 3.46 with the 5 speed. It makes a great combination. The automatics though with the 3 speed would be great with the 3.73. The diffs from the e30 series work but the rear diff cover must be replaced with the original replacing the cover from the e30. Otherwise it is a direct bolt-on. Make sure you buy the cover gasket....and have fun.

sweet deal...

a) do you think then that 3.73 is too much? i have a 5 speed as well, with a final drive of 3.25

b) what part of the differential exactly is the cover gasket? (i'm ig'nant)

c) looking in my bentley manual it shows the "speedometer pulse sender" being on the differential... how will this affect what my speedometer reads? will it read how fast i'm really going, or will it read how fast it thinks it's going without accounting for the new final drive ratio?

thanks so much

--ethan
87 535is

Yea...I think the 3.73 would be too much. With the 3.46, I cruise at 80 at 3000rpm. Which is right at the powerband of the motor. Very nice.

The portion of the diff that you will have swap is the rear cover. This cover has the rear mount that you need to mount the new diff. The cover has the speed sender on it. Before you swap the rear covers, take the one out of the old cover and reinstall in the original 3.25 cover.You must use the 3.46 sensor with the 3.46 diff and with the 3.25 cover.

Before reinstalling the 3.25 cover to the 3.46 diff you have to buy a new rear cover gasket($7)....so you don't loose all of your fluid in the first 50 miles! Make sure when you do the swap and take the covers off not to allow dirt into the differentials. Work cleanly.

You will get a 7% (roughly) increase in power distribution. The 3.73 would be a 13% increase. But you would suffer even more on the highway....proportional to speed.