Will a 735 differential fit a '91 535i???

[Robert K]

If so, what ratios were used in the 735i's? My uncle had a late 80's 735i that he said got approx. 26-28 miles per gallon on the highway. I took it for a spin and the RPM's were a whole lot lower at highway speeds than those of my 1991 535i. That leads me to believe that his had a different diff ratio than the E34's have. I love my 535i, but I'm tired of getting 23-24 mpg on the highway (going downhill, with a tailwind, a fresh tuneup, and lots of air in the tires) when my uncle's huge 735i got high 20's on the highway. I'm just wondering if the parts are direct interchanges and just how much difference in acceleration there will be. Any BMW tech junkies out there know the answers to these questions??? I'd appreciate any input.

Grace and peace,

Robert K
1991 535i

[gale]

Vine's page lists the diff ratios for various years:

http://www.vinesauto.com/diffratio.htm

I put a 3.91 lsd diff from an 89 e34 auto into my 92 735i auto and it was almost a direct swap, but the axle hubs were larger so swapped my old e32 hubs into it, simple proceedure, they just pry out with a screwdriver. Gotta take them out to replace the seals anyway.

The only other differences is from a manual diff to an auto diff, the auto has a smaller hole pattern for the driveshaft input hub, but they too can be swapped if being careful to get the preload right.

I know at one time for non-lsd diff's, the axle hubs could not be swapped with lsd diff axle hubs. I don't know if that design was carried into the e32/e34 design.

I changed from a 4.27 lsd diff that came new on mine, to a 3.91 when I did the 5-spd conversion, which puts rpm's in 5th only 50 rpm higher than what it was in 4th with the automatic when cruising at 80 mph, ~3300. I'm still contemplating putting a 3.73 into it, at the expense of losing some off-line acceleration, to gain a longer 1st gear & top end economy, but they were only available on 89 525i's and later e34 M's.

Other than that, I think the e34 M5 diff's have a different mount on the rear & don't believe they're interchangable with non-M app's.