Is a Helical diff right for my BMW?

[dougisaacs]

Hi all, I'm considering an LSD for my 2006 BMW 330i. It's a road car but may end up doing a few track days in years to come. Looking into LSDs it seems to me that a helical type diff is the type to go for as it doesn't really wear (and it could be in there for quite a few miles) and offers relatively gentle lock up which is good for the road. My understanding is that it won't lock if one wheel is off the ground, and therefore offering no resistance, but otherwise it's an effective system. I'm not clear if it locks on deceleration and therefore causes understeer and I'm interested in anyone's comments on that in particular but any other comments?

[Krikkit]

I always thought an ATB would only provide lockup when the wheels lose traction, rather than a plate-type which provides more complex locking behaviour.

[stevieturbo]

If you're referring to a torque biasing type diff, then no, they never lock. And yes if one wheel loses enough traction, all drive can be lost.

But yes they never wear as such and are quiet and mostly gentle/smooth in operation.

They need load against any spinning wheel in order to transfer the drive to the other wheel, hence they can allow one wheel to spin if it gets too slippy at one side.

Some can pre-load them internally to help prevent this though

[AW111]

I have one in an early MR2. Although in theory it needs some traction on the unloaded wheel, in practise I haven't had that happen : either it grips and goes, or both wheels spin.

[stevieturbo]

I've one in my Granada with a live axle....it's fairly easy on tight turns to get one wheel light enough that it loses pretty much all traction.

I wouldnt necessarily say that's a bad thing from a safety perspective, as it does make it safer to go hard in.
But I have recently changed it to a pre-loaded Torsen ( Wavetrac ) to help prevent this occurring. Havent been racing anywhere yet to see if it makes a difference, probably wont now until next year.

[Munter]

stevieturbo said:

... Granada ... racing

Checks profile
Watches video
ahhh

[stevieturbo]

Munter said:

Checks profile
Watches video
ahhh

Is it not normal to race one ? lol

[buggalugs]

I put a Z3 torsen in my old E30, really liked it. Very noticeably more traction coming out of slower bends you could really take the mick with how soon you got on the power. If you were dabbling with a bit of 'oppo' it was a bit more predictable, with the open diff it would sometimes grip again quite randomly, or I'd try to kick it out but only manage to spin up one wheel I never tried a plate type I understand they can be a bit all or nothing?

How useful it is on track would depend on the track I guess! Maybe try a few days without one and see how big an issue it is? Your E46 has a *slightly* more spophisticated rear end than my old shed did

[dougisaacs]

Thanks all, FYI mine's the later E90 330i. Apparently Wavetrac do a diff that gets over the issue of an unloaded wheel leading to no drive.
Anyone any experience of these?