Changing differential gear ratios

[lmcclain]

I'm revitalizing my '95 540i 6-speed (I'm the orig owner) and am considering the diff gear change. Reading posts on the subject, it seems that most people just swap complete diffs, right? My car would have a 2.81 diff and I'm planning to follow the recommendation to go to a 3.15. I believe later E34 540i's with auto transmissions had 3.15 diffs, right? Are these diffs directly interchangable? Is there a better way to go?

[Kent Carlson]

I'm revitalizing my '95 540i 6-speed (I'm the orig owner) and am considering the diff gear change. Reading posts on the subject, it seems that most people just swap complete diffs, right? My car would have a 2.81 diff and I'm planning to follow the recommendation to go to a 3.15. I believe later E34 540i's with auto transmissions had 3.15 diffs, right? Are these diffs directly interchangable? Is there a better way to go?

Call Jim Blandton and have him make a chart for the different ratios. That is what I did. I cant remember what i went with off hand but the charts showed me the low end acceleration and the highway cruising RPMs. Very helpfull.

Sorry but i dont have his number handy at work either. A lot of help i am!

[Blitzkrieg Bob]

sometimes has to be swapped from the old to the new pinion.

Other than that it usually goes pretty Mr. Miyagi like... Diff out....Diff on

[lmcclain]

Kent,
Thanks for the lead. I'll try to track him down.
Larry


Call Jim Blandton and have him make a chart for the different ratios. That is what I did. I cant remember what i went with off hand but the charts showed me the low end acceleration and the highway cruising RPMs. Very helpfull.

Sorry but i dont have his number handy at work either. A lot of help i am!

[lmcclain]

Bob,
That's exactly what I wanted to hear.
Thanks.
Larry


sometimes has to be swapped from the old to the new pinion.

Other than that it usually goes pretty Mr. Miyagi like... Diff out....Diff on

[MBXB]

Here's an earlier thread

http://www.bimmer.info/forum/showthread.php?t=5843&highlight=limited+slip

[632 Regal]

you will want a 3:46 or a 3:64 (ratios might not be exact) I went with the 3:64 cause thats what was available at the time, I thought it would be too much but it isnt. I dont get any worse mileage on the freeway and the city is actually better. The difference in city driving is unbelievable and highway is same unless I want to fly. Top end is still unreachable with 3500rpms at 100 mph.

[PhilipJCaputo]

Top end is still unreachable with 3500rpms at 100 mph.

if your only at 3500 rpms, you've still got a long way to go before redline....

[lmcclain]

Perfect. Not sure why I didn't find this before posting. L.


Here's an earlier thread

http://www.bimmer.info/forum/showthread.php?t=5843&highlight=limited+slip

[lmcclain]

Interesting. According to the upgrade info on E34.net, your stock diff was a 3.15, so you jumped quite a ways to 3.64. I was a little concerned that going from 2.81 to 3.15 would be too much. Thanks for the headsup.


you will want a 3:46 or a 3:64 (ratios might not be exact) I went with the 3:64 cause thats what was available at the time, I thought it would be too much but it isnt. I dont get any worse mileage on the freeway and the city is actually better. The difference in city driving is unbelievable and highway is same unless I want to fly. Top end is still unreachable with 3500rpms at 100 mph.