A4 Tdi Quattro, Rear locking up after losing grip... Help!

[workhorse]

Merry Christmas everyone, I havent had the quattro long and bought it for the extra traction at this time of year, Like many i couldnt resist lighting up all four wheels on a snowy car park near me, After spinning the wheels and letting off the throttle, The rear drivetrain seems to lock up as if the handbrake is on for a couple of seconds then free itself, if i press the throttle when its tight (after the initial spin) it will stay tight until i come to almost a stop then it will be free, Now i know it will either be the abs or the rear diff, How can i solve this problem> I also get the abs feeling at the pedal at very low speeds and the abs light comes on sometimes and goes off on its own, but i cant help feeling its the diff as it only happens after a full on 4wd spin and its definitely the rear, (i cant tell if its one sided or both, I dont really want to keep doing it in case something happens. Look forward to your replys people. Many thanks. Nicky.

P's The abs light does not come on when this problem happens.

[workhorse]

Abs fuse removed & has stopped doing it, unknown abs fault maybe,

[s1turbomike]

Have you managed to give the rear abs sensors a quick look over to see if there is anything obvious and also check the rigged ring around the drive shaft to see if it is complete and not rusted. The other way is to use an LED test light and backprobe the sensors with the wheel in the air and spin It by hand and see if you get a pulsing signal. Hope this is of help to you.

[mike ryan]

You can test the sensors by using a multi meter. They will all give a consistent resistance. if they are open circuit it is probably because the speed ring has swelled with rust and taken the top off the sensor.