B7 S4 Juddering/Slipping When Pulling Away at Near Full Lock

How many miles has it covered?

Does it judder only when turning to pull away or in a straight line too?
It could just be that the gearbox fluid and filter need changing. I think Audi say that the gearbox oil is a lifetime oil but a lot of people say they should be changed around 70-80k.

The gearboxes are used in some BMWs who have change intervals.

The gearboxes are made up of clusters of gears and bands that effectively ‘brake’ the outside of the cluster to increase drive steadily. As these wear they contaminate the fluid that’s lubricating and cooling them. A bit like in an engine if you don’t change it often enough problems will occur. Preventative maintenance is key to avoiding big repair bills in the future. The same fluid also goes around the torque converter which is what transfers the drive from the engine to the gearbox. If this has bad or excessively contaminated fluid going around that can also cause juddering.
I wouldn’t worry about changing the diff fluids as the front and centre one are lubricated by the gearbox fluid. And the rear one if there is jibber from that changing the oil is unlikely to make a difference as it’s only a pinion and crown wheel in the rear diff


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Only on 4x4s like a Land Rover defender or a ford ranger or something similar are the differentials all separate. On a 4wd car like yours the front diff and centre diff are all housed in the same gearbox casing that the gearbox itself is in. It’s the rear diff that’s the only separate item.

But yes at that sort of mileage it won’t hurt to change it. The only downside is I would advise using the genuine lol and filter and this can be costly alone. I’ve heard that the parts coke to around £250 and Audi only charge around £300 to do the whole job which is not a bad price cpnsidering. I’d get some quotes from your local Audi dealer and an Indy and compare but you can’t beat a genuine service if it’s cheaper or comparable


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Mine feels like it's scrubbing on full lock, I assumed the tracking needs a check, hadn't considered diff issues.

piglet14 said:

Mine feels like it's scrubbing on full lock, I assumed the tracking needs a check, hadn't considered diff issues.

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That could just be a characteristic of your car. A3s that use a transverse gearbox(side to side) and haldex set up are only activated when the front wheels spin and is controlled electronically. So when you turn on full lock the car knows this from a sensor and doesn’t kick the rear wheels in unless you floor it and get slip on the front two. Semi-permanent 4WD

On your A4 the gearbox is longitudinal(front to back) so it has an actual differential at the back of the gearbox(or as most will refer to as the centre diff) this on the Quattro are a torsion diff so it will only put the power to the rear wheels when the front wheels spin slightly faster than the rear. Under full lock as you will have an open front diff the inside wheel spins faster than all of the other 3 wheels which in turn causes the torsion diff to try and engage the rear wheels more.
This technically is a permanent 4WD set up but I think most refer to it as a semi permanent set up because if the front wheels are spinning at the same speed and the same speed as the rear wheels then the rear wheels won’t kick in. It’s only when one of the front wheels is spinning at a different speed to the rears. This will also work when slowing down as it’s a mechanical system.

It’s similar to a full time 4x4 set up in a proper 4x4 which is why you sometimes get drive system wind up. So when you jack the wheels up sometimes they will spin back to release the tension. Not so prominent in a torsion AWD but it can still happen


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Hi folks, this all sounds kinda like the problem I was having (see thread https://www.audi-sport.net/xf/threads/servotronic-steering-assist.405558/_ and it went away with a new set of tyres! I suspect the 'transmission wind up' theory was the cause on my car.

As mentioned above its more than likely a tyre wear issue. My Avant does the same when the trye are on there way out, a handy little reminder come to think of it!