The Stovebolt Site Forums The Shop Area Engine Shop Brakes Tightened by Themselves While Standing

I adjusted my Huck brakes since only one shoe was well-adjusted on each wheel. The brake pedal went down half-way but it was still driveable and I drove it to work. The truck sat all day.

At the end of the day, I hit the brake pedal and it wouldn't go down much at all. I hadn't used the parking brake (granny gear instead) and I didn't pump the pedal. Something had changed.

All four wheels are tight so it wasn't just one hinky wheel. It must be the MC. I retracted the MC plunger by about 1/16" and the brake pedal now goes most of the way to the floor.

Anyone know what might have happened? This is a new dual reservoir MC, lines and rebuilt wheel cylinders but it hasn't been driven for many months. How can a brake system almost lock up while just standing??

Thanks!

When you said "all the wheels were locked" I thought of the master cylinder pluger covering the return port so the fluid couldn't return to the reservoir.....that's why all the brakes were locked.

The only reason I can think of for them to get tight would be possibly moisture in the brake fluid??

I had a similar problem with my 51 1-ton with huck brakes, although only my rears locked up. It turned out that both of my rear brake return springs were broken or missing. The springs on my 1 ton were 3-piece, being the spring itself, and the spring hooks that slid in and out of the tightly coiled spring ends. Anyway I only needed two,but Napa ordered eight just to stock up. About half were delivered with the spring hooks having already fallen out of the tightly coiled spring ends.

Bottom line is, if you have the 3 piece spring it might have failed even if brand new.

:rolleyes:
chevy 1 -
That exact thing happened to me. The plunger in the MC wouldn't move far enough back to unplug the drain back hole. My brakes were slightly engaged all the time. I almost never figured it out and finally removed the cover on the MC, looked in and saw the problem. Turned out the MC had been assembled incorrectly. It worked great after it was reassembeled correctly.
Wally / Montana, you might check to be sure the MC is correctly assembled, especially if you didn't assemble it.

Thanks for the help. It looks like I need to readjust the MC plunger outward and then readjust the brakes.

Wally, Could you describe the system you just put in? What kind, bore, of mc, did you add residual pressure checks, are you using a proportioning valve? Did you replace the brake hoses? I'm very interested now that I've just acquired a '50 gmc 3/4 ton.

I've had Hucks lock up while sitting, and usually the problem has been failed return springs in the rear axle.

Splashoil,

I used the adapter kit from Classic Performance but ordered the MC from NAPA by number. I'll get the info to you when I return from the coast to Montana. There's no proportioning valve.

It has all new lines and hoses. I rebuilt the rear wheel cylinders but the front had seen a recent rebuild.

I'm pretty sure this was a hydraulic problem and not a mechanical spring problem. All 4 brakes had become tight and the brake pedal became fully extended at the same time. When I adjusted the MC plunger outward about 1/16", all 4 wheels loosened up and the brake pedal went down nearly to the floor. I believe the plunger was not coming out far enough to expose the relief valve.