brake master cylinder
Unmotivated automatic braking at rising operating temperatures or falling pedal pressure indicate a defective brake master cylinder.
Unmotivated self-braking action of the vehicle can, of course, have various causes. Jammed brake caliper pistons and guides, jammed brake pads, and blocked brake hoses are all possible causes. This must be checked in each individual case. However, this behavior is very often caused by the brake caliper itself, especially with the 25ZV brake master cylinders of some Audi models. If the brake master cylinder is cooled in a suitable manner in such an incident and the brake then releases spontaneously, the brake master cylinder is the culprit. In such a case, the brake master cylinder must be replaced or repaired. Repairs are possible in many cases and are particularly an option if new parts are no longer available.