Brakes Jammed on What have I done?

[blusmith]

1982 FI rebuilt 3 yrs ago and got round to replacing the booster 'cos the brakes always felt a bit spongey. Rebuild included new rotors, new master cylinder and caliper kits all round. Now the brakes seize on after about 6 or miles running. Leave the car 2hrs and I can go another 6miles!. I have bled brakes twice; I thought I had adjusted the booster thrust rod properly but Ive obviously stuffed something up. Any advice welcomed. Chris

[131]

Next time it happens, undo the 13mm nuts holding the master to the booster, you only need the master to move a little away from the mounting face. See if the brakes free up. If they do, you haven't left enough freeplay in the actuator rod. Old hoses can sometimes collapse internally, acting like a one way valve, when fluid is pushed through to apply the brakes, it can't return and so holds the brakes on.

[blusmith]

Thanks Nick I'll give that a go. I hope you are right 'cos hydraulics totally mystify me . chris

[micbrody]

I agree with 131: pushrod is adjusted too long.
I replaced my brake booster with the one from AR. I screwed down the nut and lock washer that came with unit all the way down. It did extend past the body of booster , but it looked to be within the 2mm that manual states.
When I started driving , everything felt great ; but within a few minutes , the braking became "super great"....I was realizing that my wheels were in constant braking condition. I theorized that initial driving was tolerable, but master cylinder must have been depressed slightly , trapping brake fluid in non-braking situation . As I continued to drive, the slight caliper pressure heated up brake fluid ; fluid expanded ; and more pressure placed on caliper.
I disconnected master cylinder from booster; pulled pushrod out. I removed the lock washer; and just screwed down rod with rounded end nut as short as it would go. Re-installed . Everything now works great

[blusmith]

Thanks You have described it exactly . Confidence restored -I will have a go . Chris