Broken front ABS Sensor (by me); any removal tips?

[theknack]

It had to happen, it was all going so well.

I'm in the midst of changing a broken front coil spring, and the guide I was following (which is for the Ibiza) recommended removing the ABS sensor from the hub, as some hammering may need to happen. So off I went; a liberal application of some penetrating fluid, removed the stud, and gently prising up on the sensor until.....

it snapped :/ and its left the bulk of itself in the wheel hub/knuckle.

I'll have to get the residual part out. Could I get lucky and just go gently with a drill to remove the remainder? Or would I be better off taking off the entire hub/knuckle/brake carrier and go at it that way? I guess that the ring is in the hub on these.

(BTW- I was surprised to find that this car has no detachable caliper carrier; it's part of the hub/knuckle component. I think its the first time I've seen that)

tia

tk

 

[RUM4MO]

Well, I have a 2011 Audi S4 and it chose to declare that it had a failed ABS as I reversed out of the garage to take it for its MOT!!

A slightly different situation on that car, the ABS sensors are fixed to/through an ALUMINIUM upright/knuckle, so if/when you break the sensor trying to remove it, it can be tricky to deal with the bits that remain - touch the magnetic ring that is on the rear face of the hub bearing, and that will need replacing as well.

I cracked a front ABS sensor on my wife's 2015 Polo when I was replacing the front hub bearings, the LHS change of bearing went okay, maybe it was the extra rust/curd on the RHS that causes the extra rust/curd to catch the ABS sensor and crack it, so I replaced it with a new Bosch one, the original was branded TRW probably as they supply some completed sub assemblies to car build plants. Doing that while the bearing was out was easy, no danger of causing more problems.

For the 2011 Audi S4, I've got enough excuses to bore you, but low ambient temperatures, the need to be able to get the Polo back into the garage over night as we tend to babysit for our older daughter and a lot of worrying about damaging the magnetic surface of the bearing, forced me to hand the job to my local garage who was doing the MOT, that has been delayed until next week!

So, for you with the "external" part sheared off, after buying a new ABS sensor, plenty cheap £15ish ones on ebay, I thought that I'd be clever and as soon as my S4 declared that fault and I confirmed it using VCDS, I went to ECP and bought a new Bosch ABS sensor roughly £69, now, doing that turned out to be a waste of time and money as my local will not fit customer supplied parts, which fair enough, so I'll need to absorb that loss, but, quickly having a new ABS sensor lets you see just how deep you can drill without causing any damage to the magnetic surface on the inner end of the bearing.

The hole diameter will be just over 10mm, so you can either drill down the depth that you have worked out from a new sensor, for the Polo I've estimated 10mm is a safe depth - for the Audi it is a lot more, so you can drill a suitable diameter hole and screw a suitable wood/chipboard screw down into it - then grab the head of that and pull straight up and out. Second option is to grip a suitable sized screw in visegrips, heat it up to red/white hot and force it down into the remains of the sensor, then quickly remove the visegrips and use a screw driver to drive it down further then quickly quench the area to get the plastic back to being hard and shocking the plastic while cooling it quickly. The third option is to drill down using a smallish diameter drill making a connected series of holes all round the outer edge of the ABS sensor, this in theory should leave a "peg" in the middle, this should be manipulated side to side until you feel it is loose enough to pull it up and out.

Good Luck, I feel your pain!

 

[RUM4MO]

Too late to ask now, but why did you feel the need to remove the ABS sensor to keep it safe while replacing the front springs, I've done that job on a 2002 Polo, a 2009 Ibiza and a 2015 Polo - the job on that last car was just preventative maintenance, ie replacing the springs before they snapped.

Edit:- engine Max ouput determines the size of the front brakes, the smallest, used to be 256mm so maybe close to that even although they are probably Mando and not Lucas>Girling>TRW (now much cheapness from a far away country) and calliper bolted directly to the hub/knuckle, over maybe 100 or 105PS, the set up changes to calliper carrier bolted to the hub/knuckle and bigger discs, used to be 288mm possibly a bit less now that they are now Mando, then above maybe 150PS they change to roughly 320mm with different calliper carriers and callipers most of the time. Big worry/danger with callipers bolting directly to hub/knuckles is, lots of people do their brake work, so these callipers get removed quite often(maybe) and these guide screws get over tightened - and that ends up with their threaded holes in the hub/knuckle getting stripped - there are ways to sort that out though!

Sorry to add more concerns, but being aware can sometimes be useful.

 

[RUM4MO]

My bigger issue than on your car is, on my Audi S4, the hub is part of a lump of aluminium and at the bottom like your hub, it gets bolted to the lower suspension, but on my car it bolts to 2 unequal length aluminium arms and your one gets bolted to a lower TCA swivel, so your one is easy to separate, at the top of my hub is an upright that connects to another 2 unequal arms - much more worrying!

 

[theknack]

Brilliant tips many thanks. And good luck with the S4; lovely cars, I owned a fairly standard A4 Avant B7 or some years and it was a nice place to sit. I remember the front suspension and interesting arm arrangement- very high quality.

I have the 110 1.0TSI, which explains the combined knuckle arrangement. Thanks for that info.

Re: ABS sensor removal, and why I did it. I was following a guide here for the Ibiza; closest I could find to the Arona:

Suspension arms - 6J Remove and re-fit front suspension

I had some issues finding help on this when I was doing it so I took the time to photograph what I did to write this guide and hopefully help others who attempt it. Disclaimer: I am not a professional mechanic, just a enthusiast who likes to...

www.seatcupra.net

If you glance at it, you'll see that the author recommends undoing the strut pinch bolt, wishbone bolts, prising the strut cup opening at the back, and then hammering the knuckle downwards and away from the strut. In order to get a good place for the hammer to fall, they recommended pulling the sensor from the knuckle. With hindsight, I wonder if I should have tried something else!

 

[RUM4MO]

Yes you do need to take that pinch bolt out M14 multi spline, then fit a "hub splitter or strut removal" into the back of that split in the hub carrier to ease it open "just" enough - then the hub carrier can be eased down and off the strut.

Example of that tool is Laser Tools 3396 - buying it or a cheap copy is a must in my mind.


Edit;- one thing I noticed when looking at the guide is, the track rod end nut on that car is the older type and they rust just for fun, horrible to get off, your car will have the later type which in my experience don't rust so easier to deal with.

Taking the brakes off just makes that "lump" lighter, so not necessary.

So if you have the hub carrier stripped down and off this car, it should be easy to locate the lower section of the ABS sensor and if possible break it off and knock/punch that sensor back up and out of its location - MAKING SURE THAT YOU DON'T DAMAGE THE END SURFACE OF THAT WHEEL BEARING,