After sitting in the sun or at warm idle - brakes go away...pedal goes to floor. All is fine when system is cold. When cold, booster passes pedal pump-up leak test, fails though when brakes go away when hot. Took master cylinder and booster out...noticed some fluid leak from back of master cylinder...paint on booster below master cylinder coming off. I would like to do a vacuum check on the booster somehow while off the vehicle...will auto parts stores be able to do this for me ? Ideas on which part is bad ?

BTW...bought this car not running for $400...put another $300 in it and it is running great !! Love the car...(when brakes work)

 

hmmm sounds like your brake lines are getting so hot its boiling...creating bubbles in the line. bleed them and yull be set. how often do u drive this car?

 

I first purged all the lines with new fluid...did not fix it. Talked with some buddy's that said if the booster was bad the pedal would get very hard, not soft. Put a $40 re-built master cylinder in it from Autozone and that fixed it !!

Thanks....

 

You have a failing master cylinder, it's very common. It's due to not changing the fluid every 3 years.
The fluid is not boiling.

 

This car was the best buy I have ever made...got it from a dude that could not figure out why it would not start...paid $400 for it, isssue was bad coil...$75 for coil, $10 for rotor and cap, changed all fluids and put new tires on it...got $750 total in it and it runs perfect !! 169K miles. Need to change timing belt yet, not sure how long it has been in it...