please help me!!!


I just replaced all my calipers and my brakes still stick when they heat up!!!!

help help help!!!

I doubt this is the problem but, might be worth checking. On the 5ktq I just bought, the car had the right rear caliper dangling in the breeze (prev. owner not mechanically inclined). When I went to put caliper back on, I noticed something funny. The pins that let the caliper float, were stuck (bent). I bent them straight and lubed them so the caliper could move as the pads wear down. Did you replace the bracket also? Are the calipers from a wrecker or new/reman? Anyway, I guess it might be worth checking to see if the caliper moves freely on the bracket. Can you describe what its like when they stick? Could it be something else?

Mike,

Excellent suggestion. Check for straight, lube. Pin slider calipers have to float on the pins. Caliper brakes will always slide the front brakes, at least, back into the piston if they get hot. The disk grows with heat, the piston has to retract, unless the driver rides the brake. If the intake port of the master cylinder piston is closed the fluid can't go back into the master cylinder. Rear brakes are another story, as the ratchet action of the parking brake only allows so much free play after an adjusting click, for want of a better word. If the parking brake has just clicked to minimal clearance, and you ride the brakes, you COULD heat the rear rotors to sticking point.

If the rear brakes are the culprit, try hauling back on the parking brake with a little less effort. If you are a strong guy, who really sets the parking brake tight, you may be pulling it to the next click, one click too much.

Cheers,

George

BTW, if you don't know what I am saying, try having someone hold the pedal down when you try using a C-clamp to compress your caliper to change pads. You push the MC piston in, you close the port through which you squeeze fluid back into the MC reservoir. I don't know if you CAN apply enough pressure on the clamp to depress the pistons. You've just sealed the system.

well here's the thing guys...it's not just the front or the back...it's booth...and iI don't have my parking brake hooked up at all becuase the cable has been snapped since I bought the car...but the caliper pins...this could be a problem...they are brand new but I didn't really lube them up all that well...could there still be some junk stuck in the hole where they go...I didn't think that they would expand all that much as to cause them to stick...


thoughts???

If you're certain all four are sticking, I would think it's highly unlikely the problem is with all four calipers. Most likely, something is wrong at the other end. Which I will be of no good in helping you troubleshoot. What makes the pedal return to its position when you let off? I might look at that. I think what George says about the master cylinder is most likely what is happening. If I had the same problem, and just replaced the calipers to no avail, I would probably replace the master just for the hell of it. I've done it once in my old car. The hardest part was getting my wife to help me bleed the brakes afterwards.

yeah, I'm starting to think that aswell...as they heat up the brake pedal gets really hard if that's any help to you...I might called those blaufernugen mofos and see what they say...it's nice that I only like twenty minutes from their home office...

audisloff,

Your problem is beginning to sound like water in the calipers, or the wrong brake fluid spec. And, it could be aggravated by filling the reservoir too full.

If it is water in the calipers, normal brake use will heat the caliper to where it will try to boil the water off. If the reservoir is too full, the fluid pressure has no place to expand to, so it will try to force the piston back, making the pedal hard, and applying the brakes at the same time, so getting even hotter

Audi reccommends brake fluid change every 2 years, as any brake fluid is hygroscopic, meaning it will absorb water from the air.

The correct fluid is DOT 4, not DOT 5, a silicon based fluid, nor DOT 3, one with, I believe, a lower boiling point.

If you can follow these directions, ( I don't know your background, don't be offended.), try to get a backflow preventer, or check valve
from an Oxy-acetylene, or propane, torch, along with a hose barb fitting for each end, and a couple lengths of clear nylon or viton tubing about 1/4 inch inside diameter. Attach the tubing, and, if you can see which way is "checked" operation, attach the free flow end of tubing to the ball on the bleeder screw. Slather some thick grease around the threads of the bleeder screw so as not to suck in air. Open the blleeder screw, put the other end of the hose in a container, preferably a transparent one, and pump your brakes as much as you want. Check valve will stop air from coming back into the system.

Check for water, it will settle out just as it would in gasoline.

If you find water, you now know your problem, or this should be the problem. If you don't, now might be a good time to bleed the system. You'll need a couple quarts of fluid. Refill the reservoir. I think I would start with the fronts, as Audi has 2 circuits, split diagonally. Bleed both fronts till clean new fluid comes out, keep reservoir filled, do not allow the MC to suck air, then close the fronts and bleed the rears. A quart or more should have been used, and you should not have any air in the system.

I am reasonably sure you will have gotten any water out, but, of course, not positive, as water lies in the lowest point of the caliper and the bleeders are at the highest. Hopefully, the turbulence of the fresh fluid should carry the water up and out.

Between now and when you try this, why don't you open the hood, next time they lock up and see if the reservoir IS backed up near to the top. And, before you drive, check to see if the level is at or below the MAX mark. It does need room to expand.

Vapor lock was quite common in the old days of drum brakes.

Hope this helps some,

Cheers,

George

Semi-silly question: Would the fluid be milky if there were water in the brake system? Im not sure if brake fluid is oil based or even if there would be enough circulation to turn it milky, just curious.

Mike,

I've never seen emulsified brake fluid, but I suppose it's possible, if there were enough water. Generally, there has to be agitation to keep up an emulsion, as it will seperate upon sitting, same as poorly made mayonnaise, which is also an emulsion.

Cheers,

George

Might be a silly question but who did the brake job, you or a monkey with a wrench? A coworker had his calipers done by a shop and they were sticking from the start. Something in the assembly was put in the wrong way causing the caliper and pad to stick on one side. When I rebuilt my calipers I had no problems other than trying to find the dust seal for the parking brake lever. This part is not sold by Audi or comes with the rebuilt kit! I would assume that if you had replaced FOUR calipers you would have used up at least one large container (1 Qt) of brake fluid and the system would have been flushed. A problem with the master cylinder would have been evident at the time of bleeding especially if the fluid was coming out rusty brown or black. I suspect that the problem might be with the bleeding procedure itself especially if the car is equipped with ABS. Another source for problems might be the nitrogen filled brake booster and the hydraulic pump system. I am not sure if a failure in the hydraulic system itself would cause too much pump pressure being applied to the MC. Other areas to check are the rubber hoses, I have seen a few hoses where the inside started to disintegrate and cause blockage. Also the brake proportioning valve has a tendency to rust and stick.

well I'm pretty sure there is no water in the system becuase i've pretty much bled my brake system about four times in the last year...and the last time I did it there was clean fluid coming out of all the calipers...I did put dot 3 fluid in it however...the thing that leads me to think it may not be that is that after driving for about ten miles without touching the brakes they'll just let loose...but as soon as I apply just the slightest bit of pressure to the pedal they're back to sticking again...and my fluid level never stays all that high in the resuvoir...if that helps at all...


AUDI: makers of the world's best automatic braking system
"All I had to do was push in on the clutch!!!!" writes Aaron from WI:D

Let see if I get this! Let's say you pull away from curb and while driving there are no brakes sticking. You apply the brakes and now you feel the brakes stick? How bad do they stick? Can you roll down a slight hill? What happens when you brakes are sticking and you let the car sit a few hours?

I've heard of, and had vacuum boosters fail, not apply boost to the brakes.

Is it possible for some part in the booster to actually apply permanently, the check valve, say, once you touch the brakes?

Don't wanna go get the book, just now, nor even go out to see if the '90 even HAS a vacuum booster. Will check in the AM.

If you touch the brake and it locks up, what else can it be?

Cheers,

George

5000/100/200 models don't use a vacuum brake booster instead they use a central hydraulic system that provides brake boost and power steering. I suspect that perhaps your troubles are somewhere with this system. After applying the brakes, perhaps the hydraulic pressure is not being released just as George has implied. I don't know if there is away to flush it. There is a procedure for flushing the steering rack (http://sjmautotechnik.com/trouble_shooting/susp.html#hydoil), which uses the same fluid but at much lower pressure.

Front Brakes Sticking

You should check the brake pedal play and make sure the pedal is not sticking or hanging up which is preventing it from returning all the way. If the pedal does not return fully, the brake servo piston will put pressure on the master cylinder piston and the return port in the master cylinder can be blocked which will not allow the release of hydraulic pressure at the front calipers.

The return port in the hydraulic power booster could be restricted or blocked as well but I have not seen this happen.

The return port on the Master Cylinder can also get clogged up with crud or the master cylinder piston can get stuck in the bore. In some rare cases, the front rubber brake hoses can swell up and restrict the fluid return from the calipers.

The caliper pistons can be also rusted or corroded and sticking, or the caliper mounting bushings could be corroded and prevent the caliper carrier and pads from moving freely. I have also seen some aftermarket cruise control systems cause the brake pedal from returning as well.

You should have a technician diagnose these types of problems, as you don't want to lose your brakes!

Offramp,

Good quote.

The only thing I can add is that just maybe someone in the recent past has changed the servo booster, and not adjusted the push rod to the right length. 249 m/m, 9.8 inches from the mounting flange to the center of the clevis pin on the brake pedal.

Longer, and I don't know just how much longer would be critical, and you "probably" would be partially stroking the master cylinder piston, possibly enough to cover the fluid port and not allowing fluid back into the MC as it heats and expands, and it will heat and expand on ANY vehicle, but with the port open, no problem.

I forget who said "You have to use a pressure bleeder." Though I never have, on any of my Audis, I did just read in the ABS section of my manual that "If it is necessary to bleed the brake hydraulic system after a repair operation, the system MUST (emphasis, mine) be bled using a pressure bleeding device." I never have and have not had any problems to date, but thought I would pass that along. This from my '84-'88 manual, I would suppose they're more emphatic with newer vehicles.

Sorry, I was wrong there.

Cheers,

George

BTW, where did you find that quote. Sounds like it comes from an interesting source.

Thanks

BTW, where did you find that quote. Sounds like it comes from an interesting source.

Same source that I always post and set up links from. Good old SJMautotechnik.com (http://SJMautotechnik.com) the wealth of information that this guy has posted is hard to beat. When trouble shooting my car this is the first place I look.

offramp...

to describe the sticking problem a little better...


here's what happens...I start driving. On short trips and trips with little braking(no city) the brakes work fine. However, as soon I start driving in the city and in turn use the brakes more the brakes start to grab little by little to the point I have to have my car in second gear to make it up hills(at apr. 30mph). the brake pedal is hard to depress and unresponsive. the car will role down a steep hill but not a slight hill...no chance. If I don't use my brakes for a while they'll let loose all at once. If I use my brakes shortly thereafter they start sticking again. If I park my car for a while and let it cool down and then drive it later on they work fine...the brake pedal goes down a little farther but they don't stick...

Is it possible that perhaps the brake pads/rotors might be too thick? I had a similar problem with my father’s truck. I replaced the front pads and rotors and they were sitting rather snug and everything worked. The tires rotated by hand so I didn't think much of it. We took it for a test drive and everything seemed normal. Next day my father was flagged by a motorist telling my father that there was smoke and flames shooting out through the wheels. I had to file the backing plate slightly so that there was more slop for heat expansion.

However I think that the problem is in the central hydraulic system that provides power assist. Here is what I would do. Get the brakes nice and hot, so they stick. Jack up one of the front wheels and visually check that you don’t have any binding, the caliper is supposed to free float side to side. If the pads are holding like Vice grips, very carefully crack open the bleeder valve if the fluid shoots out and frees your brakes then it is the master cylinder and power assist that is not working properly. But be very careful because you can easily get burned from hot fluid and brake parts. OR if you can get your hands on brake pressure tester gauge hook it up and check the pressure.

As George has mentioned there is a procedure for adjusting the push rod.

How long have you had this car, and why did the previous owner sell it?

Again with the brake servo, was it replaced?

Another point to check is to remove the cap from the brake fluid reservoir, the filter, too, if possible, watch it closely while someone else pumps the brake.

If you get a squirt of fluid, or turbulence at the surface, you will know that the port in the MC that is ALWAYS open with the pedal fully released, so that the MC has a full charge of fluid to pressurize the system.

If you are NOT getting the squirt of fluid, which indicates that the MC piston has completely uncoverd the recharge hole, it means you have a sealed system, now, and heat buildup in the fluid will apply the brakes, and make the pedal rock hard. This does indicate, either, the servo rod is too long, obstructing the hole, or the MC has failed, the piston cup has somehow come off the stem, and is not coming back far enough to oper the recharge port.

You CAN, by contorting yourself, or a friend, get a measurement of the length of the servo pushrod, without removing it. It would have to be probably at least an 1/8 inch too long to obstruct the recharge port.

I hesitate to suggest that the locknut on the servo pushrod has come loose and screwed itself OUT, the expected result would be for it to screw itself in, in that case.

Cheers,

Georg

I've had the car for a little over a year....as far as I know the servo has never been replaced. The guy I bought it from was selling it because he had just bought a 2000 a6 and had two other cars. He bought the car in 1991 with 21,000 miles and he pretty much told me everything that he could think of that he had done with it. he did tell me the brakes needed some work. So the brakes have stuck a little since I bought it. I assumed it was from lack of use becuase he only drove it for 6 blocks a day for two years and after I started driving it the sticking didn't really happen all that often. but they just started getting really bad in the last two months, I would assume due to the hot ass summer we've been having. So yeah, all in all, pretty sure the servo has never been replaced.

pads are definitelly not too tight. I could turn the rotors(wich are pretty worn in the first place) without a problem...

sidenote: you guys have been a big help and I really appreciate it

Audisloff,

Might be too late, but have you checked or replaced your hoses? The car IS 18 years old, and the inner liner will rot, crack, and sometimes the liner will rot one way, sometimes the other, ie, the inner liner will collapse across the hose to prevent fluid from returning from the wheel caliper, sometimes it will collapse preventing the pressure from applying the brakes, at all.

My s'in-law had his vehicle in to the garage for inspection, etc, today, and a collapsed inner hose liner was keeping the brake applied at the pass side disk. You could apply the brake, but the pressure stayed in the caliper. Wore that side almost to the rivets, although the driver's side was at 80% or better.

Another thought.

Cheers,

George

anyone know if he ever fixed this problem, because i have the EXACT same problem with my 86 5000cs tq. i replaced all the rubber lines and most of the hard lines yesterday to eliminate that as a problem. Next thing is the master cylinder. after that, things get expensive. any new ideas?