I think I have a problem with my master cylinder, if I depress the brake pedal very slowly it will sink all the way to the floor, but if I depress it fast it works and is not mushy at all. Is there air in my MC or is my MC bad.

 

are you parked or u driving..
if parked then it might be normal
if driving try this
its not the Mc it might be the Booster. it might have a leak but what you should do is get your brakes bleed frist and thenn if it is till like that then get a bottole of water then spray around your booster and pump it if you see bubbles then it is your booster...

 

It happens when driving and parked, I haven't tried it parked with the engine off though. I've bled the bakes already and there's no air in the lines.

I'll try that trick with the brake booster.

 

My master cylinder did exactly the same thing. Exactly. Turns out shitty fluid (cheap ****) had gathered moisture, and in turn made the fluid acidic. Thus, the master cylinder materical became soft, and porus inside, and the piston couldn't compress the fluid slowly. It would leak around the piston inside. Thus, mushy at slow braking, and decent when you mashed on the pedal.

Bought a Fenco rebuilt replacement for $90 CAD.

Solved my problem. Took about an hour to install, and bench bleed.

Don't take chances with your brakes, get it fixed asap.

Good luck.

 

Thanks dude, exactly the answer I needed, now it's time to upgrade.