posi trak or limited slip

[bullseyeprec]

I have a backdraft and while the bmw says it delivers something like 70/30 split traction on dry pavement if you nail it you only get 1 black mark. Now I know from the g forces both tires are pulling but is there a swap out there to get both wheels doing an equal amount of work? I am not talking about a locked or spool typle arrangement but I am used to the old posi trac units in chevy cars and while these seem to work well nothing looks more sheesy after a burn out then a single black mark. Anyone have any inpout?

[blykins]

I've never seen the diff in a Beemer....I'm assuming it's a clutch type diff...if it is, then you should be able to shim the clutches to give more friction at all times...

If that doesn't float your boat, then there are aftermarket companies that make replacement performance LSD's for them....I'm having trouble thinking of the name right now...but if it comes to me, I'll post it...just give me a little bit....

[blykins]

Quaife is the name of the company....I knew I'd remember it...

[DC COBRA]

bullseyeprec
I ordered my car with the limited slip rear-end, boyh tires never fail to spin or pull evenly. When I looked at the BDR cars, the demo I jacked up and spun the rear tires, turned liked an open rear-end, one tire going one way , the other one going opposite way. Really that was the deciding factor on me buying the car. Paid for the upgrade of limited slip and got it. I have done quite a bit of reseach on the BMW rear-end, know what is available, specs and so forth. I have talked to several road racers who run the base style rear-end that BDR uses in their BMW's, those rear-ends arereally pretty nice pieces. They are considerably stronger than what I thought they would be. The racers I talked to commented that they never heard of any body breaking one. BMW offers their limited slips in different degrees of lock-up breakaway. Factory ones are 25-35%. performance rebuilds will get you about45-50%, racing versions will get you about 75%, not recommended for the street. I ordered a new gearset with a 50% lockup, I'm going with 3.73 gears, they have quite a few choices. I presently have a stock 3.15 ratio with limited slip and at 6000 rpms in second gear with a Tremec TKO it will do 100 mph, I don't like that kind of speed capability. I like the car to be gear lowered, more squirrely, although it will break the tires loose in third gear roll on sometimes. I don't know what gears you are pulling, but I might be interested in selling my differential once I get my new diff in. One thing I like about the BMW rear diffs, they are easy to change , takes about 1 to 1.5 hours to do. There is nothing to leak out , they are pretty much sealed, pretty simple job.

DON

[DC COBRA]

Those Quaife units are about $1000 and they get $600-$800 to install in your rear-end. The stock units come with 2 clucthes each side, upgrade to 3 clutches for about $ 250 on your ls housing, upgrade to 4 clutches(race) for about $800-1000 on your housing. If you need a core the housings run about $400-600 and then you got to get them installed.

DON

[Dennis Kelley]

Hey DC

Does anyone have the phone no. or address for Quaife or email? I'm thinking about upgrading mine too.

[DC COBRA]

Dennis

I don,t have their phone number or address, the best way is to do a search for BMW REAR DIFFERENTIALS on your internet explorer. You will find several companies that will sell the Quaife assembly cheaper the factory they say. They also will setup the assembly for you with a choice of gear ratio. My setup is not a Quaife, but a reworked posi unit that holds three clutches, giving about 50% lokup breakaway, almost to tight for the street. It was ordered with 3.73 gears,almost went with 3.64 ratio, the whole assembly was rebuilt to performance specs with whatever new parts they used in doing so. I ordered thru Bimmerworld, cost complete was $1800, it leaves two even blackmarks anywhere or anytime. Oh boy, what a difference the gear change made, you talking about scary. Most of the performance BMW people are on the East coast for some reason, they were all very nice to talk to and deal with. I believe if you go to QUAIFE AMERICA on the net, you will find all the information there is on their products(just accidently found it browsing now).

DON

[Doug I]

A mechanic I know is building a SCCA BMW as we speak. I'll ask him tomorrow.