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Audi A4 Avant 1999 Wheel Motion Sensors

Hello All

I'm faced with the doubtful pleasure of renewing a front outer CV joint boot. I've read up fairly extensively on the subject and think I know of most of the pitfalls, the notorious pinch bolt et al. The one thing remaining unresolved in my mind is the removal of the motion detector sensor for the ABS system. All the accounts I have read glibly mention removing the sense head without any reference as to the best way to do so. I have held the outer part of the head as tightly by hand as I can manage and it will not move at all. There are a couple of extremely inviting flats on the head of the sensor which just invite the application of spanner pressure, this I'm reluctant to do as the head appears to be plastic and the last thing I want to do is to damage it (the cable disappears to places unknown and there are no visible junctions, hence it could be quite tricky, as well as expensive to renew).

Has anyone experienced similar problems? Did they find a a solution? Has anyone broken the head of the sensor attempting to remove it? If so, was it easy/ expensive to renew? Where is the connector for the feed wire for this item?

Thanks kindly for all assistance.

Reply to
ArthurX
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The ABS sensor is removed by pulling straight out. If yours doesn't do that it may have corrosion around it. When installed there is a grease used to keep them from seizing.

OTOH, I am not sure why you want to remove it at all because you can remove the axle by tilting the strut once it is loose and the ABS sensor has enough wire to allow this.

If you do remove it you will need to get a part called an ablative tip to place over it when inserting it again. The process is to replace th axle and then push the ABS sensor back in until it hits the hub on the axle. When the axle turns it wears away the ablative tip and the correct clearance it maintained.

The connection to unplug the ABS sensor is reached by removing the plastic wheel well liner and you will see it.

The way I move the strut to remove the axle is to first jack up both sides of the front of the car to remove pressure on either side from the sway bar. Then remove the three nuts on the top of the strut (top of the wheel well in side the hood). The rotate the strut down and remove the axle. this way you do not need to mess with the pinch bolt from hell.

Reply to
TonyJ

Dear Tony

Thanks for the extremely informative and helpful reply. The reason I wanted to remove the motion sensor was because in all the procedures I have read this part needs to be moved, if it doesn't, then that's great news. I was pondering on the necessity to remove it but decided that the most likely reason was the amount of free wire on the component being insufficient but if there's enough, that's also good news.

I was most interested to hear of your avoidance of the pinch bolt by removing the top anchorage of the strut, there is one account I've seen of tackling the task by loosing the bottom anchorage but your approach appeals a lot more - less corrosion, straight back, good access etc.

I made myself a screw powered extractor for the pinch bolt, loosely modelled upon the official Audi tool, with mine being far heavier in construction and I would have been interested to see if it worked, though not very interesting if it failed and destroyed the pinch bolt in the process. Have you ever used the official Audi tool or heard of stories of it's success? It seemed to me that the frequent approach of removing the bolt by percussion probably failed by reason of access and that also the top arm being supported in rubber bushes, this removing much of the shock from the blow.

I'd be pleased to hear your thoughts.

Thanks once again for the very helpful reply.

Kind Regards

Art

Reply to
ArthurX

I haven't ever used the Audi tool for the pinch bolt but then I am just a shade tree mechanic that like working on my car and friends. I have heard that the tool works but success is dependent on the amount of corrosion. Most people who attempt to remove the pinch bolt start after having a new replacement available in case the old one is ruined.

Let us know how it goes.

Reply to
TonyJ

Hello Tony

Yes I do have a new pinch bolt available, including the nut. What concerned me was ruining the bolt in the attempt to extract to the point of being unable to refit the nut, this being the point at which all boats are burnt - no going back. I always worry to much.

I looked at the top attachment option today and it does look good.

Regards

Art

Reply to
ArthurX

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