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again with the 87 5000cs tq brake problems

again with the 87 5000cs tq brake problems

  #1  
Old 08-05-2005, 06:53 PM
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Default again with the 87 5000cs tq brake problems

please help me!!!


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

help help help!!!
 
  #2  
Old 08-07-2005, 03:14 AM
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Default RE: again with the 87 5000cs tq brake problems

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?
 
  #3  
Old 08-07-2005, 05:23 AM
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Default RE: again with the 87 5000cs tq brake problems

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.
 
  #4  
Old 08-07-2005, 02:11 PM
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Default RE: again with the 87 5000cs tq brake problems

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???
 
  #5  
Old 08-07-2005, 04:59 PM
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Default RE: again with the 87 5000cs tq brake problems

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.
 
  #6  
Old 08-08-2005, 04:00 PM
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Default RE: again with the 87 5000cs tq brake problems

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 ***** and see what they say...it's nice that I only like twenty minutes from their home office...
 
  #7  
Old 08-09-2005, 01:29 AM
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Default RE: again with the 87 5000cs tq brake problems

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
 
  #8  
Old 08-09-2005, 02:49 AM
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Default RE: again with the 87 5000cs tq brake problems

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.
 
  #9  
Old 08-09-2005, 03:16 AM
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Default RE: again with the 87 5000cs tq brake problems

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
 
  #10  
Old 08-09-2005, 01:57 PM
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Default RE: again with the 87 5000cs tq brake problems

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.
 

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