I'm looking to get a new differential with a better gear ratio for my E34 91 540i. I know Dinan makes some LSDs. Their catalog says something like $3500 but I'm afraid to ask if that is including the labor hours. I don't need it installed, I just need the part. Can someone tell me what either just what the part costs, or could you recommend another aftermarket differential with a nice, short grear ratio for mega-fun acceleration? :)

Anyone have the Dinan differential installed on their E34? I am wondering your thoughts and impressions. Any other suggestions/thoughts on this upgrade are also appreciated. TIA

You could check out Diffs-online.

They make differentials for a number of cars. Prices might be better aswell.
PM Dan, his username is diffsonline. He should be able to help you out.

Good luck. Dinan makes a good warrantied product, but they are also the most expensive in the buisness.

Maybe a 3.91 or 3.73 lsd from an E34M5 would work?

e34nication*sp* runs a diff off of a e31.
That might work aswell. :dunno

Do you have a manny tranny?If so,go with either 3:15 or 3:46.If slushbox go with 3:46.Try Ken Baker,he is in the BMWCCA Rondel magazine.I have a 3:15 in my '95 540i 6 spd and a 3:91 in my '90 535i 5 spd.Just noticed-there is no '91 540I.

First of all.... 91 540i? Did someone rebadge it and sell it to you as a 540? I would make sure that it actually is an 8-cylinder before going through all of this hassle.

For a 540i the differentials from the e31 850's and the e32 750's will bolt right up. All you have to do is put the differential cover from your existing differential onto the new diff. For the 6-speeds I believe the optimal ratio is 3.15 (which is what I am looking for if any of you have one laying around because I need an LSD) and for the automatics I believe the optimal ration to be the 3.64. I am pretty sure the diffs from the e34 m5's will not work. In addition to the fact that they won't work I would also assume they would be more expensive than getting an e31 or e32 diff.

The e34 M5 diffs do fit because they are also the large case diff design. But as said, the M5 ratios are not suggested for the 540i gearing. Some e31s came with ratios in the 2.65. So, an auto e32 750i 3.15LS is optimal.

The e34 M5 diffs do fit because they are also the large case diff design. But as said, the M5 ratios are not suggested for the 540i gearing. Some e31s came with ratios in the 2.65. So, an auto e32 750i 3.15LS is optimal.

which ratio is optimal depends on whether or not the car is an automatic or a manual.

http://www.bmwe34.net/e34main/maintenance/transmission/differential.htm

I have a 3.15 LSD I will be pulling off my car next week (525i though).
What is this thing worth?
Thanks...

Woopsie.. I meant 94 540i.. doh! It is the 5speed auto.

Your diff ratio is a 2.93 according to the TIS. I would suggest going 3.15 up to 3.46. The e32 750i is a very good candidate for the 3.15LS. I am not aware of any models of the big diff that has the 3.46 that will bolt right in, but 3.8L 6spd M5 guys have put them into their diffs. You probably just have to find the gears from any big diff (including euro 6spd S52 M3s, e39 M5s, e46 M3, etc.) and get it put into your case, but that entails a whole rebuild and setting.

The diffs from the 4.0L e34/32, M5, 750i, and e31 are all big diffs and will bolt in. Regular 6cyl and 3.0L V8 e34's diffs have the smaller case diff. Unless you are planning to use a 3.64 that will make your car rev really high on the highway, then the 3.15 is probably your best option. If you had another gear, say the 6th in the 6spd, then comfortable highway cruising may be achieved with a 3.64 from the e31.

People have put real high (numerically) diffs into their cars, but that is their own comfort level (and fuel mileage sufferage), Good luck with your endevour.

i put a 3.73 lsd on my 525i and damn does it make a difference. I drive it around the city with high end amusement!