[Scion owner]

I have a 2009 scion tc manual trans. My brake pedal intermittently sinks to the floor. There are no fluid leaks we installed a new master cylinder and bled the brake system twice. And STILL the brake pedal randomly will sink to the floor.
what else could be causing this to happen??

 

[Dallasrhi]

You could have a brake caliper leaking. I blew out a caliper and replaced it, but when I did I couldn't get a pedal and has weak brakes so the car would struggle stopping. I eventually had to replace the master cylinder also and that helped my issue out. It's possible that the brake booster could be going out but I don't know of anyways to test them.

 

[merdone]

Maybe there's still air in the lines somewhere.