Need some help Brakes locking up.

[jtm311]

Hello Guys I need some help. After long drives my rear brakes are starting to lockup. I can fix it by pulling the check valve from the boaster.
It only happens on long drives.

With the car running I pulled the check valve it is working and has good vacuum.
I wrapped my exhaust where is gets close to the brake lines.

Also when the brakes start to lock the pedal gets rock hard.

Any help?

Thanks
John

[David Pozzi]

Make sure your pedal can return fully without any interference. Check that the brake light switch is not limiting return. If anything holds pressure on the booster rod it can prevent it from releasing fully. Another big issue with power brakes is to have the correct length rod from booster to master cylinder. I have had rods that were just a little bit too long and prevented the master cylinder from uncovering the vent port. Next time try loosening the two master cylinder bolts a little and see if the brakes release. If that helps, the rod may be too long, but first make sure the pedal rod is not being held in.
I see a lot of these issues over on Team Camaro, many are due to the booster to master rod length.
David

[jtm311]

Thank yoy David I will give it a try..
John

[MonzaRacer]

One or two washers under the master cylinder on the booster studs, if this helps you have a rod length issue. Also if you have a car that had drum rear brakes have you removed/replaced the pressure check valves with 2 lbs rather than the original 10 lb ones. Some cars run them in line. This might be one other possibility.

[TT302Z28]

I had the exact same problem a few years ago in my 70 Chevelle. I did exactly what MonzaRacer suggested and the problem went away.

[jtm311]

Thanks Guys I think I have it fixed. I used a smaller washer on the the master cylinder the pedal is soft at first but grabs as you press down. No look up on the last long run