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,

 

[RUM4MO]

Any good progress yet?
I was checking the parts number of the front ABS sensors on your 2018 Arona and they are the same as for the 2015 VW Polo, so my statement about how far down from the top of the cast hub carrier it is safe to go sticks, ie 10mm after maybe 12mm the shape of the sensor changes from the roughly 10mm diameter towards the thinner rectangular size that its lower end is.

 

[theknack]

I moved forward and then......I moved back :/

I ordered a new ABS sensor, and followed your advice when it arrived on estimating the depth. However, it was proving tricky to decide how far to drill down, and I didn't want to risk hitting the reluctor ring. So I decided to go medieval, and remove the entire strut. That way I could rotate it fully on the bench and see how the removal efforts were actually working.

And this is where I hit what I will call snag no 2; at this stage, almost the only thing left to remove from the lower parts was the track rod end nut. Old school me decided to do old school things and wind off the nut about halfway, then whack it with a hammer. The result should've been a free track rod end; instead, we got a slightly mushroomed bolt head and TRE ball stud :/ (I'm an idiot, and you should never do this, especially when you own a fancier ball joint remover....)

Anyway, I then did what I should have done first thing and put my ball joint remover on it, pressed it as loose as I could, and got the bolt off- with some difficulty. So a new TRE will be going on too..... btw, for anyone reading this in future- these TREs have a hex socket underneath to allow you to slot in a key and brace is against turning. A useful inclusion.

I then carefully drilled out the broken ABS sensor. Tense but I got there; there's no way it would have drifted out, it has a couple of small tangs on the side to prevent movement. I then connected the new sensor up and turned the key; no warning lights on the dash, so it 'sees' the sensor. Hopefully the ring will be ok, it seemed to not suffer any damage in the drilling.

At this point, I thought- why dont I just get the strut back in with the new spring and see what's what? And that would allow me to slip the TRE stud back in and unwind the TRE itself from the shaft (after I'd measured the threads of course). And thats where I decided to temporarily give up- I found that my general-use spring compressors were almost completely wound in, which terrifies me, and still had a few mm they needed to go to let me get the mount and cap bolt in. And I was just about to take my life in my hands doing this when one compressor made a gentle ping and one of the feet slipped off :/ seems that they dont like being compressed as fully as they were.

So I've paused for now. I'll think about the springs etc overnight.

thanks for your interest btw

 

[RUM4MO]

I think over my messing with cars lifetime, I've bought 4 sets of spring compressors, the 1st set were given out on loan to a work colleague and I got an LP to copy, things dragged on and he left the company, oh well! So I replaced them with roughly the same design/type.
Then maybe 18 years ago I bought yet another, or a second set to have along with the replacement set as I was dealing with tapered springs, ie VW Polo, this next set had double "grips" at the ends, then a year or so later, as my 2000 VW Passat 4Motion broke a front spring, which the AA replaced on my sister's driveway down South, and I felt the need to replace the other side and these springs were quite long, I bought a longer set which were a set of 3 and had clips/clamps over the jaws to sort of trap the spring coil - but, the threads on them are now looking worn - maybe not lubricated often enough, so I'm a bit nervous about trusting them the next time I need to work on road springs, so maybe I'll try to replace that set.

Maybe a tip for the future, if you need to work on the other side of your Arona, as it has cast iron hub carrier and the steering link/arm is part of it, try using 2 hammers on the end of that steering arm/link after removing the TRE nut - a quick tap on both sides at the same time usually works - something that I couldn't attempt on my 2011 Audi S4 with its alloy hubs!

Yes, the hex insert in the TRE ball stud is useful, but with a lot earlier cars, like the 2002 VW Polo, the TRE ball stud was made of crappy soft metal plus the nut was as well and the nyloc insert in that nut had turned into something extremely hard just over a period of 4 or 5 years - so, I ended up distorting-swelling the section of the TRE ball stud so that it was now bigger than the threaded hole in the TRE - game over, so it took me maybe 3 nights after work in deep winter, after getting home by bus as I gave my wife my car to use, cutting down and across until that nut could be ripped off, damaging the TRE in the process! That was my introduction to working on VW Group products, thankfully at least at that area, as you (and I) have found, quality has improved a lot over the original "pure Skoda CZ" quality.

Again, more Good Luck, as I've got older, I seem to have become more risk averse and always consider compressing road springs as being a high risk activity.

Having a second set of spring compressor does help, just another tip/advisory, the last springs that I worked on, on my wife's 2015 VW Polo front, had a tendency to wander off and away from the "tight up against their stop" position on the strut lower cup as I slackened off the compressors, maybe some of that was due to the compressor threads being tighter as they were now worn, but that caught me out on the first one, and it needed re-compressing and moving the spring coil back round to its stop.

Edit:- why do potentially easy/simple tasks end up being messy???

 

[theknack]

Great tips and you remind me of myself and your adventures! I too consider spring wrangling a risky thing, and treat it with a lot of caution and trepidation. In fact, these days I'd say I definitely have the 'fear' when it comes to them. Its that one job that always gets the heart rate up.

And I'll watch out for those springs progressing on the cups, that would be incredibly frustrating an not good for my BP

Simple tasks becoming messy? Absolutely. Its a law of nature.

 

[theknack]

Update on the patient: after some careful measuring of the springs, I surmised that my compressors weren't long enough, so picked up a £25 set of 330mm capable ones. Using one of these, and siting it so that I could catch 4 loops of coil, and a smaller compressor on the other side meant I could get it compressed enough for the bearing and cap to bolt on.

And then I thought about the TRE.....it was a bit mushroomed at one end (as was the original bolt) and when I compared it to the new TRE I'd picked up, I noted that the old one seemed to need a Torx 45, new one only needed a 30. This showed me how distorted the existing one was, so I whipped it off. (I bought a 24mm open ended spanner to get this done right).

So its all good, car is driving again and at the right height all round, and I've booked it in for a front wheel alignment at a local place first thing tomorrow.

thanks for the help!

 

[RUM4MO]

Good stuff, I've found that lots of aftermarket but good quality car parts, use slightly different "sizes" like as you have found the "holding insert" type and size, and, slightly more annoying, the "AF" size of the nut on the top of front strut pistons - typically I just buy a new correct "AF" nut from VW Group and fit that to avoid the next owner getting a surprise.
The "is it a Hex or Torx?" can cause harm to these TREs if you use the wrong type.

I ordered up a new spring compressor to replace the one with the worn threads - same item different brand/supplier set of 3, so playing safe for the next time!

My S4 finally goes to get its front RHS ABS sensor replaced tomorrow and hopefully an MOT, typical for me, I started worrying that my diagnosis concerning the ABS fault was not fully proven to be 100% correct, so I spent a couple of hours this morning checking it again and found that the original ABS sensor is now a short circuit and not just lowish DC resistance value, I also checked the "still good" front LHS ABS sensor's DC resistance and it was what I had expected it to be. The garage I am using seemed to be a bit concerned to accept this job without first carrying out his own diagnosis, I can understand that although some of us are quite capable of carrying out diagnostic work on our cars.

 

[theknack]

Absolutely right on the aftermarket parts thing; variability can be an issue, and measuring out beforehand saves a lot of time afterwards.

Good luck on the MOT; if you can, report back and let us know how it goes.

and thanks again

 

[RUM4MO]

Well!
My garage was let down by their parts supplier - wrong sensor supplied, they either have a car lift failed, or so other reason why a van is up on it and causing delays to their work through put, so the owner has asked permission to use the ABS sensor that I bought and tied to the cabling and plugged into the car - just to give the ABS controller an easier time as the car’s failed sensor is now a short circuit.

On a lesser level, the new spring compressor set that I bought, could not get delivered due to ambiguous signage being placed at both ends of our local access or “B” road.

So, as per normal, when things go wrong, lots of things also go wrong.

Now to phone that garage and ask for a print out of the exhaust emissions - when they finally test my car.

 

[RUM4MO]

Well all tasks completed, 1.5 hours labour for removing and fitting a new ABS sensor, which seems fair enough, if I was confident that I'd get that job done in mid winter just before that MOT I might have done it myself - but I wasn't, maybe okay to do that job mid summer with 6 months before the next MOT.

Anyway, just because I like to try avoiding ending up in this situation, I've ordered up a pack of 5 "M6 wood to metal dowels hanger bolts threaded" - these are just a metal dowels with a 6mm wood thread at one end and M6 at the other end, my plan will be to extend the M6 section by using an M6 joining piece/nut and some M6 threaded bar + maybe some 20mm M6 washers to act as thrust plate and a short length of 15mm steel pipe + another M6 joining piece/nut to act as a jacking nut. So after shearing the "top" section of the ABS sensor, I'll either drill a pilot hole or heat up the dowel + threaded bar, screw the dowel down into the remains of the ABS sensor, fit a suitable length of 15mm steel pipe over that, then the couple of 20mm washers followed by the M6 joining/piece/nut - and tighten that nut down to draw/pull out the remains of ABS sensors from the hub carrier/knuckle - time will tell if that idea/plan will work, but at least within a few days, I'll have collected all these parts together and store it as a kit. All good fun, so that car will be 14 years old in 15 days and the only MOT that got advisories was the one in year 6 at my Audi dealer who considered that both lower suspension pivot pins on both side were showing signs of wear - and I've not replaced any of the suspension yet or had any advisories.

I just need to examine the "repair area" check that the wheel, if taken off, was put back in in the same "position" and swop one bolt on each front wheel to a locking bolt and refit bolt caps/trims, and read, record, clear all stored fault codes.

Then try to find the next problem before it causes trouble?

 

[theknack]

Thats actually a great idea; I'd never seen those dowels until you mentioned them above. That should work, and it's a creative way to get it done too. And keeping excellent cars like this on the road is what its all about.