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Changed rear brakes - ABS Problem now?

Discussion in 'A4/S4 forum(B5 Chassis)' started by GhostWKD, Sep 26, 2011.

  1. GhostWKD
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    GhostWKD Member

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    [Sep 26, 2011]
    Hi All,

    Recently changed loads of stuff on the rear axle of my A4 - changed the discs, pads, bearings, new caliper on one side etc. Since then had an ABS problem - slowing to a stop from slow speed feels like the ABS is kicking in and makes the whirring noise of ABS stepping in and stopping the pedal going down etc. It used to put the ABS warning light on directly after changing all the above, I then replaced the ABS rings as the only piece of the disc/pad setup that hadnt changed and now the ABS warning light doesnt come on. But despite the ABS warning light now not coming on, the car still has the ABS kicking in when coming to a stop from a slow speed.... does anyone know what could be causing this and how to go about fixing it?

    ABS all worked fine before changing discs/pads/caliper etc
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  3. rossohlen
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    rossohlen New Member

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    [Sep 26, 2011]
    I recently did mine and had a whole heap of difficulties with the ABS... But thats another story... Is there any chance that the new ABS rings could be lose and spinning on the disc (i.e. at a different speed to the wheel) which could make the computer think the wheel is locked up? Is it ONLY when stopping from slow or does it always do it? I'm no pro but i would check to see if the ring is bent (i.e. so the sensor picks up a reading only some of the time - i.e. if it bends away from the sensor which could also make the computer think the wheel is locked), or whether you have knocked the sensor (looks like a gold-ish bullet and slides back and forth in its mount) so that it is further from the ring than it should be? Also, is it clean?
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  4. GhostWKD
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    GhostWKD Member

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    [Sep 26, 2011]
    New ABS rings are pretty solid, got them fitted by a garage as I was struggling to get them fitted. Think they were blowtorched until red red hot and then fitted and left to cool down, so pretty rock solid on there. Checked them before fitting and they seemed spot on.

    The sensors both looked a little dirty but nothing major, I guess they could have been knocked whilst faffing with bits though - is there much adjustment to these or a very narrow tolerence at all?

    Cheers,
    Alex
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  5. tangerinedream
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    tangerinedream Member

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    [Sep 26, 2011]
    as long as you use audi sensors you should be good, there are problems with aftermarket ones i know but if they used o.e ones and made sure they wer facing the correct way im unsure only way to check is to take off and inspect?
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  6. mike-a
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    mike-a Member

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    [Sep 26, 2011]
    Log block one in the abs module with vag com while driving below 10-12mph and letting car come to a halt.One of the speed readings will fluctuate.This is your problem sensor.The sensor will probably be ok (unless it's taken a hard knock or the actual wires are damaged) as will the new sensor rings.The problem will be that the sensor isn't close enough to read accurately at low speeds.First check the disc for play on it's stub axle.If there is any re adjust the stub axle nut until there is no play but not tight enough to cause excessive drag as this will lead to premature bearing failure.If there isn't any play then gently tap the rear of the sensor to close the gap between it and the sensor ring.Note the sensors can corrode in place and be stubborn to move.Don't go mad with the hammer and smash it.
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