Thread: Mushy Brakes?

Two things cause mushy brakes:

1) Leaks
2) Compressible elements in the hydraulic circuit

As for leaks, this does not necessarily mean external leaks (although they also apply). You can have an internal leak in your master cylinder that will definitely cause mushy brakes. The easiest way to diagnose this is to stand on your brake pedal. If the pressure builds, peaks, but then slowly goes away and the pedal goes to the floor, you have a bad (leaking) master cylinder (or a hydraulic leak somewhere in your system).

#2 covers air to expanding brake lines. The flex lines near the wheels can wear out or be saturated with a foreign substance such that they lose their ability to remain rigid under pressure.

What I can say is that I hunted down air in my system for months to try and stop mushy brakes. It finally dawned on me that I was ignoring my master cylinder. I tested it and replaced it - brakes are like a rock now.

Originally Posted by SJAndrew

The easiest way to diagnose this is to stand on your brake pedal. If the pressure builds, peaks, but then slowly goes away and the pedal goes to the floor, you have a bad (leaking) master cylinder (or a hydraulic leak somewhere in your system).

This is exactly what it's like. I can 'pump' the brakes to get it to stop about a third of the way down, but once I'm stopped, it slowly sinks to the floor, and I doubt it's a leak, since fluid levels have remained high, and I've never noticed any leakage in my garage.

Originally Posted by Chernobyl

This is exactly what it's like. I can 'pump' the brakes to get it to stop about a third of the way down, but once I'm stopped, it slowly sinks to the floor, and I doubt it's a leak, since fluid levels have remained high, and I've never noticed any leakage in my garage.

The master cylinder can leak internally.

You don't lose fluid - the internal rings are worn and it's allowing the piston to push past what should be a sealed interface within the master cylinder itself.

There is some good information here.