I can apply the brake pedal and then release it and the pedal comes back to normal. But the brakes hang up like someone is still pushing the pedal down. After several miles the brakes will release by themselves. This happens on an intermittent basis. I was thinking it may be the hydraulic brake booster but with a cost of over $500,I would like to know if anyone else had this problem before trying to find that part. In addition, the brakes have been maintained and fluids flushed at regular intervals. Any help will be much appreciated as I love the car, but the cost of some of the replacement parts are very expensive. It is a 1991 audi 100
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Re: 1991 audi 100 brakes hang up
I believe that it is probably sticky brake calipers. This is a much more common problem and is more likely. You could test this by jacking up your front end and supporting the vehicle safely. Then apply the brakes, then let off of them and try to spin your wheels manually. Calipers should only cost about $40.00 each or so. Sometimes they especially like to stick when the pads are worn and/or the rotors are out of spec.
Good luck. Let me know if this solves your problem.
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I guess either the brake pedal linkage is maladjusted or perhaps not fully returning so the master cylinder fluid inlet is remaining closed. In that condition when the brake fluid expands as it grows warm under normal use it cannot escape back into the reservoir and so the brakes are applied until the system cools down.
You can check this quite simply - when next the brakes are applied momentarily release one or two brake bleed *******. If that frees the brakes it will be time to take a close look at the pedal linkage.
The condition also sometimes occurs after the replacement of the brake booster and/or brake master cylinder by folk throwing new parts at the car instead of fitting them..
There must be a clearance between the brake booster pushrod and the master cylinder piston and in the absence of service tools , careful and precise measurements must be made.
I once had a car where the brake booster failed due to fluid leaking from the master cylinder and the brakes would auto apply and not release on that car.
WHEN YOU APPLY BRAKE PEDAL, do you see brake lights come on ? if no then the switch is not working fine ! switch turns lights on when you depress the pedal, releasing the plunger, lights go out when you release the pedal. this switch has a fuse @ fuse block. check it ! if ok, and brake lights do not come on replace switch, & mount properly in bracket.
If the brakes are stopping the jimmy, it could be a hydraulic problem. check brake fluid level in master cylinder. If it is overfilled, fluid can expand when fluid heats up and can apply brakes. also,bad brake hose can trap pressure in caliper and apply brakes. Also check brake pedal and booster adjustments. other possibility is caliper/hardware (mechanical) is hanging up and not releasing. If drum brake in back, check adjustment and/or stuck wheel cylinder.
This is a common fault often caused by low battery voltage, before you start taking expensive actions with the park brake modules etc get your battery checked for 100% efficiency.
Hope this helps, good luck.
By "sticking" I am assuming that you mean that the brakes are staying applied (calipers are not releasing)and burning the brake pads and rotors up.
The most common cause of this is brake hoses.
The hoses that connect your calipers to the steel brake lines have an inner lining and a reinforced outer "shell". sometimes the inner lining tears loose from the outer shell inside the hose. (It cannot be seen by "looking" at the hose.) The inner lining then starts to act similar to a "heart valve" where it allows fluid to be pushed down into the caliper, then collapses inside the hose, blocking the fluid from returning to the master cylinder when the pedal is released. This can happen just because of the age of the hose, but is more commonly caused by someone allowing the caliper to hang by the hose while replacing the brake pads without using anything to support the weight of the caliper.
To diagnose this condition, raise and support the vehicle and remove the wheels. Make sure that the transmission is in "Park" (Automatic Transmission) or "Neutral" (Manual Transmission) and apply the parking brake. Then start the engine and apply the service brake. (Press HARD on the pedal) Shut the engine off, release the service brake and open the bleeder screws on the calipers. If brake fluid squirts out of the bleeder screw under pressure, then the hoses are the cause of the calipers not releasing.
For front brake pads replacement you need only usually wrench set, inclusive 7 mm allen key also. But for rear brake pads replacement you need obligatory a special caliper piston pressing tool, in order to press back rear caliper piston with parking brake automatic adjustment!!! For front brake pads. First you must verify yours front brake disc diameter: 280 mm or 288 mm. (On my car y have 288 mm). After that you can buy the brake pads (with wear sensor). For change front brake pads you must raise vehicle, remove wheels, extract the retaining spring of the caliper, and remove the caliper as follow: 1. Do not disconnect the brake hose from the caliper, and do not allow the caliper to hang by the brake hose! 2. Remove top and bottom caps (on back side of the caliper) for access to guide pins, then unbolt and remove them from the brake carrier. Remove the caliper. 3. Now you must thoroughly clean the brake calipers (free of grease). 4. Remove outer brake pad from brake carrier. 5. Pull inner brake pad out of brake caliper piston. 6. Check up the brake fluid level on the reservor, and emptying if neccessary! 7. Push piston back into brake caliper housing. 8. Install inner brake pad (with expanding spring) in brake caliper piston. (Arrow marked on pad - if exist, must point in direction of brake disc rotation when vehicle is moving forward). 9. Install outer brake pad into brake carrier. 10. Bolt brake caliper housing to brake carrier using two guide pins. Tightening torque is 25 Nm. 11. Install both caps. 12. Insert retaining spring into brake caliper housing. Important: Depress the brake pedal firmly several times while the car is stationary so that the brake pads adjust to their normal operating positions!!! Check brake fluid level and top up if neccessary!!!
First of all you will need to raise the wheels off the ground. Check both sides to see if they are both holding. Here is a list of what can cause the hanging in order of probablility;
1) Caliper or Caliper hose. (If the caliper is not free it won't release the pressure from the pad. Always replace the hose with the caliper because the hose may look good, but can collapse internally holding the pressure.
2) Master cylinder. Not likely but possible.
3) ABS is engaging. This can be caused by a short, it is rare, but it does happen. The short is telling the system that the wheel needs to be applied.
The cable was probably not reattached to the throttle body, or the wiring for the cruise module was not plugged back in. The VW/Audi cruise control system does not use engine vacuum, it uses it's own vacuum pump. Vacuum runs from the pump/control module to the vacuum reservoir that pulls on the throttle cable. The is also another vacuum line that runs to the brake pedal, which is a safety feature (press the brake pedal and the vacuum to the vacuum reservoir is instantly cut, releasing the throttle and disengaging the cruise control.)