[mef]

Hi all,

This thread is of great Interest to me and has got me thinking!

I have an E87 1 series asphalt rally car which has the E90 M3 stock diff on 3.85 ratio. The engine is an E36 S50b30 3 litre producing around 300bhp and I have a Tractive 6 speed sequential gearbox which has drop gears to make the overall final drive into 4.6:1

I have been using the car now for over 3 years on mainly UK asphalt rallies plus a couple of Belgian events too.

The car is generally very good but one thing that I have suffered with from day one is severe understeer which I have so far been unable to dial out. I've tried all sorts of front and rear spring rates and anti roll bar combinations to no avail and I recently realised that the diff is the only item that I've never changed or thought about. I have had experience in the past of fitting an over tight lsd that caused considerable understeer in a rwd lightweight kit car so I was wondering if it could be the M3 gkn diff that could be the source of my problem?

I have a spare lsd unit so today I conducted a test and found that the lsd has a considerable static preload, it seems to require quite a lot of force to break the drive between the shafts.

So maybe this is the problem, the diff is very tight and will only get tighter once the differential wheel speed is sensed. Also my car, although heavy at 1250kgs is probably a lot lighter, especially at the rear end than the roadgoing M3 that the diff was designed for.

So I am possibly looking at fitting something like an E39 M5 LSD which I understand is a conventional plate LSD like a ZF or maybe a modified version, what do you think?

Any comments or suggestions would be greatly appreciated!

Cheers

Martin