Who can lock up their rears ?

[Mikes2]

Surely if the rears lock up, the ABS isn't working correctly or am I missing something

[S2central.net]

There's not enough braking effort at the rear to engage the ABS - at least with the handbrake anyway.

When I stand on the middle pedal I can feel the ABS modulating alright.

More I think about it, I don't think it would be easy to lock the rears with the handbrake as the Torsen centre diff cannot allow the rear axle to stop rotating.

But on an open centre diff equipped UR you could lock the rears if ABS was switched off - right ?


Paul

[Audi_CQ]

Have no problem locking the rears even on dry tarmac Have converted to RS2 rear setup so not the same calipper problem as org. brakes

Cheers,
Roger

[s2driveruk]

thinking about it i have managed to use the handbrake in snow to get the bum end to break away into a slide so it must have slowed the rear axle enough......

[Keeper of The Kitten]

Am I being a bit naive here, but isn't the handbrake a cable operated device, and not connected to the hydraulic braking system in any way?

ABS won't make a difference to a totally independent cable operated system.

The Torsen diff would make a difference though.

__MDC__

[whakiewes]

I never had a problem in a new A4 that was torsen equipped. I can lock up the rears in an STi, EVO, Eclipse GSX, etc. all with limited slip centers. Torsen is actually further away than just a plate/clutch type locking mechanism. A clutch type locks whenever there is (X) amount of difference in speed, or front/rear in an AWD setup. A torsen locks when one side of the diff has more applied torque than the other, i.e. only under accelleration. There is no deccelleration effect with a Torsen, which is why it is rarely found on a race car. Under normal circumstances, the Torsen distributes power/torque 50/50. As one wheel or wheels break loose, more torque is being sent there because its the moment of least resistance. Think of an open differential. The inside wheel spins because it has the least resistance. If your rear wheels are spinning, the torque curve (atleast for a second) will go to the differentials polar end, which would be 10/90. The Torsen senses this and locks in order to maintain a 50/50 power distribution. So if your rear wheels are spinning, and getting 80% of the engines torque, it will shift this to the front yielding the front getting 50 rear getting 50 to stop whatever from spinning. I hope this somewhat helps in understanding how the Torsen doesn't effect the rear wheels from locking. In my 05 A4 1.8T, with the clutch in I could lock the rears as long as I would like.

I think your problem is with the braking mechanism vs. the car. Under no accelleration the diff is doing nothing. The new Haldex system is different, which doesn't allow you to do the same. FWIW with steel braided lines, carbon/ceramic pads, and ATE Super Blue fluid, I can lock the rears in both rain and dry.

Wes

[philS2]

Was out for a wee run round the island in my Coupe tonite. Bedding in a new set of stock front pads as the MOT beckons next week... I almost judged the old ones to perfection as I have nearly everything for the 996 conversion.

Anyway... cos I do so few miles on mine, the brakes needed a good workover so as to scrub any rust of the discs all round and to keep the rear adjustment mechanism working.

Whilst my handbrake happily holds the car on a steep hill... I cannot make it lock the rears while moving - even on loose surfaces with the clutch depressed.

Sure my brake fluid could do with a change and yes I have most of the stuff for the rear vented conversion. Neither is going to happen before next weeks MOT.

Just wondering how if my rears are normal are significantly below par... I have a vague memory of being able to lockup the rears on gravel when I first got the car....


Paul

saying that,i'd expect it to be like trying to lock up the fronts without vacuum assisstance.

[S2central.net]

Is it just me that doesn't understand the last two posts here ?

The torsen NEVER locks - it can only slip - providing a maximum 70/30 percent torque split in either direction. Torsen is a limited slip differential by definition.

And what has vacuum assistance got to do with anything ? The S2 has hydraulic assistance.

Since I started this thread, I have discovered my rear discs to be shagged out. When I replace them (tonight fingers X'd) I hope to test some more. Under normal driving conditions I don't think the handbrake will be able to lock the rears...

However on a trailing throttle on loose surface (gravel/snow) I think it *should* be able to lock the rears - at least temporarily at low speeds. That's the theory anyway.

Paul

[philS2]

hydraulic assisstance then.

[anton]

well i dont have an s2 (yet:mischeif but my kv quattro(series 3) manages to lock up the rears with the handbrake very easily and it will drift with the rears locked and the fronts rolling for a good 20m, not that ive tried it in our car park when everyones gone home

ant

ps.mine also has the torsen cetre diff and mine has no probs......