Audi 100 brakes problem

[pimpdriver]

hi,

Audi 100 2.3 quattro avant, G reg.

The brakes were a bit ropey and was pulling to the left under braking, so I had the following done yesterday:

new front discs (Brembo)
new front pads (ATE)
new rear pads
1 NSR caliper
fluid changed

The garage reported that the OSR caliper was sticking slightly, and the NSF caliper was hard to get back in, but went back in with some coaxing.

I drove it 100 miles, bedding the brakes in gently. On the motorway today it felt down on power, so I pulled into the services and stopped, without using the brakes at all. The rear discs were too hot to touch, the fronts were cold. I thought it was something to do with the handbrake cable.

And getting closer to work it dove to the left under braking again and when I stopped, that wheel was hotter than the other side.

I took it back to the garage and they released the handbrake cable on the OSR (as it was sticking, a new one is on order). They then replaced the NSF flexible hose, as they thought it was kinked and not letting the caliper return.

However, after a test drive, and a very good bleed of the system, the NSF caliper was still sticking. The only way to release the caliper was to undo the union on the ABS unit leading from the caliper to the ABS unit (I watched them do it).

On the 50 mile trip home, I pulled into the services again, not using the brakes this time. When I touched the discs (carefully!), the NSF was cold (bizarre!) but the other 3 were hot!!! ) even though the NSR had a brand new caliper on it........

What is going on?

Shall I replace the other 3 flexibles and see what happens? (I want to try and eliminate simple things 1st).

Is it (as the garage suggested) the ABS unit (I don't think it is).

Any other thoughts?

Cheers,

Steve

[amanda]

Master cyl?

[TheTwelveQuidKid]

Bent or worn caliper slides can cause uneven braking and binding brakes. Also, in rare cases, worn wheel bearings can do this as well. A master cylinder might also be the culprit if the piston isn't returning fully. Some cars ( I don't know specifically about the A100) have many moving parts between the brake pedal and the master cylinder. Some have bushes which can rust or seize up, and if this was happening, it might cause the brakes to bind, however if it is only some of the brakes, not all of them, I wouldn't have thought this is the most likely cause.

When you allow the car to freewheel to a standstill from a slow speed, can you feel a slight jolt just as the car actually stops moving. If you can, this confirms one or more of the brake pads are in contact with a disk. Jacking up each corner of the car and trying to rotate each wheel by hand will also give a clue as to which brake is at fault.

If a car pulls to the left under braking, it usually means one or more of the brakes on the right side of the car aren't working as well as those on the left. With uneven braking, a vehicle usually pulls towards the side which has the highest braking effort

Any caliper which doesn't release correctly is suspect. If you removed a caliper from its housing, and got an assistant to lightly press the brake pedal, you should (if the caliper isn't shot) be able to see the piston move out and then return very slightly. If it doesn't, it's probably time to replace it. A brake caliper with a piston which doesn't release properly also wont exert full braking effort on the wheel either. Brake calipers sometimes become distorted and this can make the pistons stick in the bores. It used to happen a lot on the old 1980s Fiats and Lancias which had alloy calipers.

[pimpdriver]

bugger! 3 more calipers then at £80 each then?

What confuses me is that at lunchtime, the NSF caliper was sticking, while later on, it wasn't and the other 3 were..........

The "bomb" pressure test does about 10 pumps before the pedal goes hard.