Brake noise and scraping

[Flurry]

Symptoms:

 

- when the car is warm (driven for more than 20 minutes or so) and going faster than about 45mph there's a fairly intermittent squeal/squeak, which goes away if the brake pedal is pressed.

 

- very occasionally at slow speed (walking pace) the brakes scrape/grate slightly, and if pressed harder the car shudders slightly.

 

- I'd have said both the noise and scraping come from the front brakes, possibly the right hand side if I had to guess

 

- I can't see any marks on the discs from something making contact, though I've only looked at the outside face of each disc

 

- Other than the above the brakes perform fine, stopping well and not pulling to either side. They were fitted new about 6k miles ago, after the last set lasted around 50k miles.

 

I'm struggling to locate the source of the problem here, as are the local garage, who've yet to be able to replicate the noise or scraping and have failed to find anything physically wrong with the brakes, though I'm not entirely sure how much they disassembled them to check. Does anyone have any ideas of where I should be looking next?

Edited 4 July, 2015 by Flurry

[rotodiesel]

The Teves brakes on the front of the B5.5 are badly designed in as far as the outer pad is not prevented from staying in contact with the disk when the brakes are released. This is because there are no "axial" locating springs on the outer pad - unlike the spring clip on the inner.

 

The consequences of this are either that the outer pad moves in the caliper body with a "clonk" each time the brakes are released (and sometimes when gently applied) or that they squeak because they stay in light contact with the disk.

 

Slightly worn disks develop a wear ridge which tends to cause the pads to stick to the disk - the problem generally doesn't happen with new disks. My car developed the "clonk" when the replacement disks had been in use for about 30k miles. The cause baffled me until I saw the fret mark on the inside of the caliper body where the outer pad had been sticking and moving in jumps. I then realised what a poor design it was.

 

My fix was to run the disk with the engine in first gear and apply a file to the wear ridge on the outer face and outer circumference of the disk, taking the sharp step off it. Instant fix - the noise went and has not returned at all.

 

More carefully designed cars such as products from BMW and M-B use a similar Teves caliper but with extra axial pre-load springs for the outer pad in the caliper - obviously to avoid this problem. A car park examination of a few cars with silly Al wheels will verify this.

 

Time for the Wolfsburg engineers to get out of the pub - although the brakes always work to full efficiency, even when the outer pad sticks. Poor design.

 

rotodiesel.

Edited 4 July, 2015 by rotodiesel

[jimbof]

Interesting, my drivers side is doing this clonk on occasion shortly after having come to a stop. I am on the second set of pads for these discs and indeed they have a bit of a lip on them now.

[Gaz]

My NSF has also started to clonk.  Haven't looked yet.  I like Roto's idea of filing any lip off.  At least I now know what to look for 

 

Gaz

[rotodiesel]

Remember that the inner pads on these Teves calipers are handed - although superficially they look the same. There is a rotational direction arrow stamped on the leaf spring which engages with the hollow piston. If fitted incorrectly, the inner pads will "c o c k" in the caliper body and cause noises.

 

Not all (fast fit or dealer) mechanics realise that these pads have to be fitted correctly. I always check for this first in the case of brake noises - before moving on to the ball joints....

 

Much as I like the AWX/GGB combination in my Superb, I've never ever owned a car with so many design defects or features which make servicing likely to be problematic.

 

rotodiesel.

Edited 4 July, 2015 by rotodiesel

[Flurry]

as far as a lip on the disc goes, I can't see any, and there really shouldn't be given the discs were changed along with the pads around 6k miles ago. It sounds like the squeak could well be caused by the pads not fully returning into the calliper then. If this is the case then I can live with the noise. How would I go about checking that the pads have been fitted to the correct hand?

 

As for the scraping/shuddering, is this likely to be related, or a totally different issue? Grit in/on the pads?

[rotodiesel]

Take the inner pad out and check that the arrow on the spring clip corresponds to the forward direction of rotation of the road wheel.

 

rotodiesel.

[Gaz]

Slightly worn disks develop a wear ridge which tends to cause the pads to stick to the disk - the problem generally doesn't happen with new disks. My car developed the "clonk" when the replacement disks had been in use for about 30k miles. The cause baffled me until I saw the fret mark on the inside of the caliper body where the outer pad had been sticking and moving in jumps. I then realised what a poor design it was.

 

My fix was to run the disk with the engine in first gear and apply a file to the wear ridge on the outer face and outer circumference of the disk, taking the sharp step off it. Instant fix - the noise went and has not returned at all.

 

rotodiesel.

 

If I raise the front up and put it in first to file off any ridge, am I going to end up with a fault due to the rear wheels not turning? (no VCDS here :( ).

 

Gaz

[rotodiesel]

Just pull the speed sensor out of the knuckle - then the system doesn't know what you're doing.

 

rotodiesel.

[Flurry]

It occurred to me last night that I'd been looking at the outer edge of the disc when looking for a ridge/lip. Upon closer inspection last night there does seem to be a very slightly raised lip on the inner edge, so that probably answers that.

 

As for checking the pad fitment, that sounds straight forward enough so I'll have a go at it soon

[rotodiesel]

The outer lip is the one which causes the problem, judging by the fret marks on the inside of the caliper. I didn't bother with the inner lip - and I fixed the problem completely.

 

One obvious point - if you use the car as a "lathe" you must re-fit 3 wheel bolts with spacers to keep the disk true to the hub.

 

rotodiesel.

Edited 7 July, 2015 by rotodiesel

[Flurry]

The outer lip is the one which causes the problem, judging by the fret marks on the inside of the caliper. I didn't bother with the inner lip - and I fixed the problem completely.

 

One obvious point - if you use the car as a "lathe" you must re-fit 3 wheel bolts with spacers to keep the disk true to the hub.

 

rotodiesel.

 

hmm, possibly back to the drawing board then, given there's no outer lip.

[rotodiesel]

It doesn't take much - a finger nail test should find a lip. A few thou is enough to allow the pad to stick on the disk and for the backplate to move in the caliper body. Remember with this design of caliper, the pads will tend to pivot around the point where the ears engage with the bracket slide rails. The pads are not going to stick inboard.

 

If you take the caliper body off and look on the inside, where the outboard curved edge of the outer pad backplate contacts it, there may well be visible fret marks. It's slight, but there if you know what to look for.

 

As soon as I found the fret marks on my car, I knew what the cause was. Two minutes with a file on the disk cured the problem - you only chamfer the step edge - don't attempt to remove the step.

 

rotodiesel.

[Flurry]

It doesn't take much - a finger nail test should find a lip. A few thou is enough to allow the pad to stick on the disk and for the backplate to move in the caliper body. Remember with this design of caliper, the pads will tend to pivot around the point where the ears engage with the bracket slide rails. The pads are not going to stick inboard.

 

If you take the caliper body off and look on the inside, where the outboard curved edge of the outer pad backplate contacts it, there may well be visible fret marks. It's slight, but there if you know what to look for.

 

As soon as I found the fret marks on my car, I knew what the cause was. Two minutes with a file on the disk cured the problem - you only chamfer the step edge - don't attempt to remove the step.

 

rotodiesel.

 

This is beginning to sound beyond my somewhat limited mechanical abilities, I think it may be garage time.

 

1.) When you say inboard do you mean the inner face of the disc, or the edge of the disc closest to the axle?

 

2.) When removing the calliper body, are the pads and hydraulics all held in place? (I'm only familiar with mountain bike hydraulic discs)

 

3.) you mention removing the speed sensor - is this vital?

 

4.) as for "re-fit 3 wheel bolts with spacers to keep the disk true to the hub" - I had possibly foolishly assumed that removing the wheel would not loosen the disc or hub?

 

5.) when refitting the calliper is there any kind of alignment with the disc that needs to be done?

[rotodiesel]

I can't give you a blow-by-blow guide to taking this lot apart. if you're not familiar with doing this job, it's best left to an expert. Brakes are not to be messed with.

 

To answer a few of your points:

 

 

Inboard - edge closer to the axle.

 

After removing the guide pins (7 AF Hex key needed) the caliper body can be pulled off. The inner pad will stay with the body as it's clipped in. Hang the body up to avoid straining the brake hose. If you let it drop, the CV joint boot may be damaged (favourite dealer trick).

 

The speed sensor just pulls out of the knuckle - unless you've let it rust in place. If you run a single wheel by differential action you might trigger an ABS fault. It's better not to provoke it - the sensors on my car will pull out easily by hand.

 

The disk will be loose on the hub unless you bolt it back on. Spacers are needed as the bolts will foul.

 

No alignment is required on refitting, just careful assembly with copper based anti-seize on the pad ears and bracket runners, and I use a very light smear of silicone grease on the slider pins to stop them picking up on the rubber bushings. Don't over torque the slider pins.

 

Advance the pads to the disk before driving the car.

 

rotodiesel.

[Flurry]

I can't give you a blow-by-blow guide to taking this lot apart. if you're not familiar with doing this job, it's best left to an expert. Brakes are not to be messed with.

 

To answer a few of your points:

 

 

Inboard - edge closer to the axle.

 

After removing the guide pins (7 AF Hex key needed) the caliper body can be pulled off. The inner pad will stay with the body as it's clipped in. Hang the body up to avoid straining the brake hose. If you let it drop, the CV joint boot may be damaged (favourite dealer trick).

 

The speed sensor just pulls out of the knuckle - unless you've let it rust in place. If you run a single wheel by differential action you might trigger an ABS fault. It's better not to provoke it - the sensors on my car will pull out easily by hand.

 

The disk will be loose on the hub unless you bolt it back on. Spacers are needed as the bolts will foul.

 

No alignment is required on refitting, just careful assembly with copper based anti-seize on the pad ears and bracket runners, and I use a very light smear of silicone grease on the slider pins to stop them picking up on the rubber bushings. Don't over torque the slider pins.

 

Advance the pads to the disk before driving the car.

 

rotodiesel.

 

I've read the above carefully and I appreciate your detailed explanation, but I think you're right in that it's probably best left to an expert. Thanks rotodiesel

[Flurry]

Follow up to the original:

 

- the shuddering was caused by the bracket that holds the speed sensor on the front passenger side wheel having corroded slightly, moving the sensor out of alignment and skewing the reading. This caused the abs to kick in momentarily, which is what I was experiencing as 'scraping'. Once the bracket replaced the problem has gone away (at least for now)

 

- the squealing when in motion seems to have gone of it's own accord, hopefully to remain gone