Brake problems One rear disk getting hot

[ianw]

Hi All,

I guess I should reintroduce myself as I haven't been on the forum much for the last few years, I live in Switzerland and I have had my Misano red RS4 from new (mar 2001), its only done 53'000 Km (not miles) but these were mostly long trips and the car was then left for months before the next long trip. I live quite close to work so preferred not to do short trips in it.

For those interested Most of the Km's were done in the early years and since then family circumstances have changed dramatically but I have resisted any pressure to sell it as its the only car I have fully specified and then waited 9 months for it to arrive and to my mind and use there is still no better car out there, I need 4WD because well its Switzerland

about 4 years ago after one particularly bad winter the brake disks rusted up, this time it was bad and no amount of driving was going to clean them up so I opted to buy new disks and pads all round, although I have tinkered a lot haven been bitten once many years ago trying to bleed a clutch on a triumph dolomite plus not knowing enough about swiss regulations I opted not to go with the popular b7 calipers etc and just get replacement disk and pads, I don't track day it and only once have the standard brakes been an issue and that was after a trip to Arosa - a really nice twisty route, no I don't baby it I have seen 175 on the speedo but I find the brakes ok for my normal driving.

Anyway this week my wife used the car and phoned to ask if it should be "squeaking" after more info and a quick risk assessment i advised her it was ok to drive the short distance home, then she phoned to ask if it was normal for a wheel to be so hot, after checking sure enough one disk was getting really hot so I suspected a sticking pad and as it was anyway time to switch to summer tyres off with wheel. On Inspection I see that the plastic coating/enamel etc was coming off the caliper and this I suspected of trapping the pad so It was sticking, so I cleaned it off and then tried to push the piston in the caliper back in, I have the correct tool but it wouldn't move, its a while since I worked on it but I don't remember that this was difficult to do before. anyway running out of time I copaslipped everything and managed to get the caliper back over the pads. the wheel turns but not quite as easily as the other side.

Driving to work this morning I notice it is still hotter than the other side so I guess a pad is still touching.

Sorry for the long intro BUT should I be able to easily turn the piston and also push it back into the caliper, if not what is likely to be wrong . Handbrake system semi stuck on, auto adjust mechanism faulty or maybe something else.

As paint plastic coating etc is coming off he calipers should I renew them, I don't really want to spend 5K unnecessarily on brakes for a car I don't use so much ( I have a G4 defender we mainly use now as the family has gotten rather large) however if it makes sense then maybe now is the time to do it.

I see on the sticky it says fitting rs6 calipers as a direct replacement for the b5 ones but then I read about fitting the newer rs4 calipers and disks - what is the latest/current recommendations. Should I just refurbish my rear calipers, is this very difficult and whats the best/easiest way to bleed them - I have used the bleeding kits that attach to a tyre but I have a compressor now and maybe there are better versions now, I have never done this on an ABS system - as a motorcyclist I know that the front brakes are much more important than the rears, but should I replace them with a better system or will I get the same corrosion problem happening again.

IanW


I am hoping to get at least another 10 years from it although I do consider swapping it from time to time, there is a nice tr6 in the local garage but that means lots and lots of tinkering and I have a few bikes in bits plus for the money I could get it would be Impossible to replace it with anything near as good.

[HEKTOR]

Hi,

It sounds like the caliper is sticking. You can easily buy new calipers or i am sure you could remove the existing calipers and have them refurbished.

I have a similar issue with my rear calipers, i will have them refurbished the next time i am having work done on the car.

[ianw]

I will take it off again and have a look at the weekend, thanks for that I hadn't considered the caliper not moving only the pads sticking and also that the piston was stuck as I couldn't "wind" it back in. Off to Germany in a month so would prefer to take the Audi (last year I managed to average 120mph for a full hour even with my speed limiter wife installed )

[TopBear]

Hi Ian, you sound like you're in the same world of pain as I am. I've just gone through similar problem, and am just in the process of re-assembling everything now, so fingers crossed it's resolved.

I noticed quite a few months ago, there was a significant rotational vibration coming from the rear brakes when applied (verified by just pulling up the handbrake on its own whilst driving). I stripped the pads and discs off and noticed one side had a stuck caliper sliding pin, so that was fixed, and I had the discs milled down in case there was a slight warping which was causing the vibration , and put it all back together and everything seemed good, (or so I thought).

I then had to leave the car standing for a few weeks whilst I was away in the states, and my brother drove the car, and called me advising the brakes were making an awful noise. I was surprised because they had only been apart a few weeks earlier. So last week I stripped the discs and pads off and could feel that one of the caliper pistons (UK passenger side) was stuck hard, nigh on impossible to wind back in with the correct caliper rewind tool. I also noticed that the piston dust seal was coming apart at the caliper. So I took the opportunity to remove the caliper from the car and stripped in down removing the piston by winding it out and removing the internal 'square' seal which I could see was trashed. I also noticed that the whole area around the crown of the piston was badly corroded. So that was all cleaned up , and new seals refitted (internal and dust seals) as well as stripping the the caliper pins out, smoothed them down, re-greasing them, and fitting new boots, as one of them was punctured. That piston and carrier is now moving much better, so I repeated the same on the drivers side, as I had the seals anyway from the kit, and figured it is good practise. I test drove the car, but the vibration was still present

So my theory is that the discs are the cause of the vibration, but the root cause which was overheating the discs was the sticking caliper. So I've now bought new OEM discs and pads and will fit them in due course.

My theory is that as it was sitting with the handbrake cable applied for a long time (3 1/2 weeks), and due to the combination of the corrosion this has stuck the caliper hard with the pad against my newly milled discs, and warped one of them. So fingers crossed with a free'r moving caliper and new discs this should all now be resolved.

I also had some left over VHT (very high temp) paint lying in the garage, so have given the outside edge of the new discs where the vents are a few light coats of this to hopefully reduce the rust getting a grip so quickly around the edge area as my car isn't garaged, and I live in a 'very wet' area of Scotland!

As far as upgrading, the RS4 rear discs are a decent setup, and whilst you could upgrade the rears there is fair bit of theory that you could unbalance the braking, by increasing the rears if you're not doing the fronts at the same time, I've upgraded the front's to B7 spec, but doing both may also present problems with the master cylinder not being up to the task. Again a lot of conjecture, as some say their brakes are spongy, and some don't after upgrading.

As far as bleeding goes, from what I've read it's no different to other cars, easier to do if there are two of you, one pressing the other opening and closing the bleed nipple, work from the furthest caliper from the Master cylinder to the nearest. You only need to use VAG-COM when you drain the system entirely, otherwise it's just the standard process. Perhaps PM Grizz or Doug to get clarification, but's that's my take on the various posts I've read.

[ianw]

Hi Topbear,

It does seem I have the same problem, thinking about it when i put new disks on a few years ago I noticed a pad imprint shortly after but put it down to putting the handbrake on when hot BUT it could be that caliper was also starting to stick then. Do you mind me asking where you got the seals from or do you have a part number(s) I can't seem to find them here although I have found complete calipers so in the worst case I can go that route.

I am considering a disk upgrade it seems possible to get the quattro upgraded disks from germany, but does anyone know if they all rust up like the originals, I know the answer is to drive it more

[PhilT]

Same problem with mine. Will either get the calipers serviced or buy a new pair as the paint is coming off.

[TopBear]

Here's the OEM part numbers for the seals\boots

B4 RS4 Rear Caliper (Lucas) Seal kit :- 4D0 698 671 (1 kit contains caliper seals for both calipers)

8E0 698 470 - 1 set of boots for guide pins (only contains 2 boots, i.e. for one side, so buy 2 packs if you're doing both calipers)

Rear B5 RS4 Caliper £266

[ianw]

Thanks for the info, I had decided to just swap the caliper so I went to the parts supplier and they didn't have it in stock and as time is getting short I booked it into the stealers, just for caliper and pads I hope. When next in UK I will get a kit to do the other side, then next year I will probably put quattro disks all round and maybe the rs6 front calipers. I have found a source in germany but its a 4 hour drive away so I need to get the car ready for that. Back to tinkering with my G4 110 - plenty to do on that