Hey guys, would anyone be abl to help me out with this?
After driving for maybe 15, 20 miles or so, my brake pedal goes to the floor. It comes back after alittle bit, and barely stoppes durring the mean time. I just put in a new master cylinder, bench bled it, bled the system, and even cross bled it. I'm not loosing brake liquid, but getting air in it if that makes sence? Anyone have any ideas on what it could be?

 

Wait... So your brakes will work fine in the driveway, but only after you drive 15 to 20 miles, the pedal will go to the floor?

 

Yup. They eventually come back. it's really weird and never seen anything like it.

 

How much life does your brake pads have?

 

Around half. not even a year old. I'm replacing them this weekend and see if that does anything at all.

 

how about your booster?

 

As far as I know it's fine. it's durring long drives with no braking. I mean I slow down downshifting and use them when I need to, but seems to happen at the same spot every day. I was thinking contaminated fluid but it comes out really clean when I bleed it. Is there a way I can check the booster?

 

yup yup..sounds like a vac leak or break booster.....yup yup yup....pull it off and put a new one on there, it wont hurt anything....

 

google search how to test your booster they have some quick simple tips to see if its bad or a vacuum leak.

 

Alright, thanks for the help, i'll see if that works.

 

An easier way to test the booster, is to pull the vacuum source and press on the brakes, but I will almost guarantee that the brake pedal will get really hard.

 

did you adjust the free play when you changed the master cylinder? if not correct can make brakes do weird things.