Brake issues?

Question

my brakes will hold a little bit of pressure when my car is off but as soon as i turn it on it loses all pressure. there are no leaks and i have blead the brakes.... some say this is the master cylinder failing any other opinions? also about how much does a place typically charge to replace the master cylinder?

Answer 1

sounds like a bad booster or like the other guy said a leak in the vaccum lines...

Answer 2

check valve in the booster or vac. line

Answer 3

best way to tell is to pump the brakes fast and hard while the engine IS NOT on. the pedal should go really hard. keep your foot down on the brake really hard and start the car. the pedal should go all the way to the floor. if it does the servo and cylnder isnt broke. if the pedal doesnt pump up till its hard then thats your servo + cylnder

Answer 4

It could be the master cylinder or the booster. Take it to a shop so you can replace the correct part !!  A vacuum leak at the booster can cause the same symptoms !!

Answer 5

I agree with user 1. I've had master cylinders fail on me just like what you are describing. IT will hold pressure SOMETIMES, and go to the floor at others. If it indeed the master, have the booster checked as well because the brake fluid can leak past the seal of the master, which is located at the back of the cylinder where it meets the brake booster. The brake fluid deteriorates the rubber diaphragm of the booster, causing it to tear or "perforate"...do you hear a "WHOOOOOSH" when you depress the brake pedal? If so you could have a leak in the booster. Either way, PLEASE have your car fixed NOW because this is a very VERY dangerous condition, both to you, and anyone else on the road with you.