[jim69bird]

I have a 69 firebird with PB. 4 wheel drums. Today the brakes locked up after about 20 miles of driving and the pedal rode very high.

I struggled to get it home, when it cooled off the car was able to move.

Is this master cylinder or vacuum booster? or is there an adjustment in the brakes that needs to be made.

[Pontiac Dave]

You might have a faulty power booster check valve, or a collapsed manifold to booster vacuum hose.

[Murf]

You might try changing the brake fluid if it's been in there awhile. If it has drawn moisture it can expand as it heats up and make the brakes drag. Good Luck.

Later, Murf

[Bill Eveland]

All 4 brakes locked up? I would also check your flex hoses, when they come apart internally, they will act like a check valve.

[LPete]

The booster pushrod that operates the master cylinder is probably too long. The master cylinder piston is pushed forward enough to cover the compensation port that goes up to the reservoir, so pressure can't escape when it builds up in the brake lines. When the fluid heats up it expands and applies the brakes. You can tell if this is the problem by opening a bleeder screw on a wheel that's locked up. If it releases pressure and spins freely this is probably the problem.