Rubbing brakes

[miketheman2k]

Hi all,

Since I bought my S4 I've always had a slight squeel in the brakes when in use, and I decided I would wait until I needed a new set before doing something about it (hopefully just changing the discs/pads would be enough)

However, in the last couple of days things have gone bad. My rear brakes are now squeeking a bit when not using the brakes, and the rear left one sometimes grinds at lower speeds...makes my car sound like a bloody nova! [img]images/graemlins/24430-audibash.gif[/img]

Am I right in thinking that the rear brakes are quite easy to take apart? If I was to g-clamp the piston back in would this sort my problem?

Thanks in advance!

Mike

[runrowsam]

I've got almost exactly the same problem on my nackered old BMW, but it's on the left front caliper. It sounds like a siezed caliper, which is basically just where the cylinders are a bit frictious and can't back off the disc very easily. I took mine apart and g-clamped it back, but it didn't make a a lot of difference. But I certainly recommend trying it, it's not that big a job and it could easily work. If you can, try and get some vaseline or similar stuff in the sides of the cylinder itself, but make sure it's nowhere near the pads or disc!!!

Rock on
Sam [img]images/graemlins/thumbs.gif[/img]

PS - When you g-clamp it back, push the dylinder right back, then loosen the clamp by a few centimetres and pump the brakes again. Do it a few times just to improve your chances of freeing it up.

[miketheman2k]

Cheers Sam, I'll give that a go and report back!

Mike

[SJS]

If the back pistons on an S4 are like an A4 they screw in and out and you need a tool to do the job easily.
using a G-clamp is not possible on them and without the tool to push and screw at the same time you will have bother.

[Carps]

In fact, using a g-clamp with any force will result in you needing new calipers [img]images/graemlins/frown.gif[/img]
I'm not too sure about the use of vaseline either...

You can get a piston wind in tool from somewhere like Halfords - Draper do a generic one that fits the Audi/VW range for about £10.

[runrowsam]

The wind in tool does exactly the same job. I used one of those a while ago, but it was a friend's, and afterwards I couldn't be arsed to go over to use what is basically a glorified version of the clamp!

With the G-clamp it's ok so long as you wind it slowly, and use a big plate which covers the whole surface of the cylinders. Pressure has to be applied evenly, and straight down the cylinder/s.

As for the vaseline idea, that's only for around the cylinders, since they sometimes catch against the caliper itself. Usually caused by brake dust and general skank getting in all the little cracks.

By all means check it out with someone who's proper in the know, since I'm only a chap like you who's looking for a cheap and easy answer! I've done it myself though, and it's been fine, but of course I don't have an S4.

Rock on
Sam [img]images/graemlins/thumbs.gif[/img]

[Carps]

I'm pretty sure you'll find that on the rear calipers, the wind in tool is essential. It is not a glorified g-clamp. If you try to use a g-clamp, it won't get you anywhere as the piston doesn't just press in.
The fronts are different. A g-clamp is fine as the piston does not wind in and out. I believe the winding action has something to do with the handbrake mechanism.

Regarding the use of vaseline - it will just melt. If you want to lube it you should use the proper stuff - copper grease. Realistically if the piston is sticking you should find out why. If it is corrosion then it should be fixed properly unless you want to come a cropper. If is is just gunk, the break degreaser (or some other source of tri-chloro-ethelene) will get rid of the muck and should free it up.
It is not necessarily a sticking piston that causes the rubbing. It could just be one of the pads sticking, in which case you may just need to remove the pads and clean up the runners and apply some suitable lubricant. If you had a horrible graunchy noise, then maybe one of the pads is worn down to the metal ? As you have had rubbing for a while this could easily be the case. An inspection of both pads should show this up, as opposed to just peering through the wheel and checking the outer pad

Whilst on the subject of winding the piston in, there is a school of thought that suggests with ABS systems you should clamp the brake line to and then release the nipple when you do this to stop any contaminated fluid passing back into the ABS pump. Personally, I have never done this and not had a problem, but it is worth considering...

Good luck.

[miketheman2k]

Right, I've bought a brake-piston-screw-clamp thing (was £20!!!) and will check it out this evening.

One final question, are the calipers held on with the standard allan key bolts, or is there something clever going on there too?

Cheers for your replies [img]images/graemlins/roundeyes.gif[/img]

Mike

[SimonS4MTM]

They are standard bolts either 13mm or allen bolts