Master cylinder?

[LIRS6]

Mushy brake pedal, basically goes straight to the floor. Developed fairly rapidly. I can pump the pressure back up, but then it dissipates quickly again. Checked fluid level - it's fine. Am I likely looking at a bad master cylinder? Any other thoughts? Anything I can check myself?

TIA

[mdegracia]

Parking brake cable corroded and keeping caliper stuck? Or a seized caliper. Master cylinders rarely go bad.

[hahnmgh63]

Mileage? They can go bad an aren't cheap. It's important to flush your fluid every couple of years, dirty fluid can prematurely wear the Master Cylinder. Always try to pressure bleed rather than the old method of pumping the pedal with someone at the bleeder. On an old cylinder you run the piston past it's normal operating limits by doing this and the old piston usually has some pitting/oxidation on it and it wears the seals like runnning sandpaper over them.

[LIRS6]

Master cylinder it is. After it is repaired, the beast will go on the block. After 147k thrilling miles, I'm ready for a change.

[905084]

That's a lot of good miles. Curious as to what you are going to replace the beast with?

[LIRS6]

That's a lot of good miles. Curious as to what you are going to replace the beast with?

GL550 is my intention

[LIRS6]

I asked dealer to place the dead master cylinder in the trunk - he said there may be a "core charge" - has ANYONE heard of such a thing for a master cylinder?

[905084]

Very common for a lot of parts. If the part was new there shouldn't be a core charge as they didn't sell you a rebuilt one.