86 5000S Brakes lock
 

On hot days in summer every once in a while the brake peddle starts to get lower and lower til it gets to the floor. The brakes are locked. I step on the gas hard and the car moves very slowly. I let off the gas without hitting the brake and the car slows to a stop. If I turn off the engine and wait about ten minutes everything goes back to normal. Does anyone else have this problem?

RE: 86 5000S Brakes lock
 

Pedal moves down on it’s own and applies break pressure? I think your 5K is possessed and you need a priest to perform an exorcism.

Did you try to lift the pedal up? It sounds almost, as if the break booster is leaking and applying pressure on it’s own. The first thing I would try is to bleed the breaks and replace all the fluid. Perhaps it is vapor lock due to air or water (water has a low boiling point).

RE: 86 5000S Brakes lock
 

Some times I think this car has a mind of it's own. I have had this problem for years. Last summer I bled all the brake lines and I thought the problem was gone until now. I do have to check the booster because sometimes when I start the car and hit the brake it will go all the way down.

RE: 86 5000S Brakes lock
 

On my 91 1CQ I had the brake pedal sink to the floor only once in the 3.5 years that I have owned it and it happened right after I bought the car. It never happened again, so I have no clue as to what caused it. I suspect it had to do something with the master cylinder. I had intermittent sinking pedals on my Mitsubishi and Toyota it turned out to be a worn master cylinders. I suspect that in your case it has to be the similar problem. I haven't studied the Audi hydraulic system in great detail but I suspect that the "break bomb" (a.k.a. accumulator) is probably leaking the pressure into the master cylinder. Did you replace or inspect the Master Cylinder?

RE: 86 5000S Brakes lock
 

I changed the master cylinder yesterday. The brakes feel a lot more solid now. The peddle going to the floor problem is going to be a wait and see deal. Last summer I drove to Florida and stayed a month, had no problems at all go figure.