The Stovebolt Site Forums The Shop Area Engine Shop Brake Locks up revisited

1954 Chevy Half Ton.....
My passenger front brake is locking up again. I thought cleaning the brake shoes and hub did the trick, it didn't.

I've been looking at the brake wheel cylinders on both front brakes. With the hub off and looking at the action when the brake peddel is applied *looks* ok.

Taking the shoes off and pushing the piston of the wheel brake cylinder on the locking brake side (passenger) with my fingers the whole unit moves back and forth real easily (maybe too easy?).
I'm not compressing the spring but moving all the innards from front to back/back to front through the cylinder. Doesn't *feel* hydraulic.

On the driver side (the side that doesn't lock) the piston and innards move back and forth not that easily about half as easy as the locking side. Kind of *feels* hydraulic (like I am pushing fluid).

All this is done with brake fluid in the system and the brakes have been bled. And there is No leaks.

I've swithed the shoes and hub around and that makes no difference, passenger side still lock up.

SOOoo My questions are should the innard of the wheel brake cylinder (piston/piston cup/spring/piston cup/piston) move Real easily back and forth in the cylinder?
Which cylinder should I think about rebuilding first?
Could the problem be the master cylinder?

Another thing after driving the vehicle and using the brakes carfully about 10 times the locking up *seems* to go away but comes back after everythings cooled down.

Whew! Tia, Kip

Did you ever check the master cylinder to see if the push rod stop plate had been installed backwards???
DG

When you say it "locks up", is it a sudden grab? Is it just a pull on the steering wheel or does it leave a black mark on the pavement? And does it let go when you take your foot off the pedal?
Is the driver's side even working?
Are both sides adjusted the same?
The lack of hydraulic "feel" on the right side is compelling, but I'm not sure that air in a wheel cylinder would cause such a condition.
I've seen bad hoses cause some odd problems, but usually they act like a check valve, and don't allow the brakes to release when there's no pedal pressure...at least on discs.
It's generally good to try to figure out a problem before just throwing parts at it. Fortunately, I think these brake systems are relatively simple and replacement parts are inexpensive.
Best luck, and keep us posted.

cm

I would suggest that it is never wise to rebuild one wheel cylinder. Conditions on both sides should be made as "equal" as possible. It sounds like there is a possibility of either the wheel cylinder sticking or the flex line acting as a one way valve. When a brake drags, it will heat up and eventually become less efficient. This may give the impression that it is not locking up at that point.

The passenger side brake is leaving a skid mark when brake is applied and brake disengages when brake peddle is released.
Again with both hubs off it *looks* like the shoes are working properly.

Should the piston assembly be so easy to push from side to side?

Tia, Kip

I'd suggest changing both wheel cylinders for brand new (not rebuilt) ones, and also the flex lines. It sounds like there's something sticking on the driver's side that's allowing the passenger's brake to get all the fluid pressure. The most likely suspect is the flex line. The problem is most likely to be a restriction opposite the side that's locking up. I'd concentrate on finding out why the driver's side isn't working- - - - -not wasting any more time looking at a brake that's obviously doing what it's supposed to be doing.
Jerry

I'm with Jerry on this. You can get new front wheel cylinders at Napa for 18.00 each-I just bought a left one this week. At that price, why mess around with honing and rebuilding?

Thanks Guys! Will mess with this more when I got a chance.

Adios, Kip

Also, you can't clean soiled shoes, gotta replace them,
Scott

Similar problems I have seen personally were;

1. Flexible line broken on inside allowed fluid to make a bulge on the outside portion of the line. Held the one cylinder longer than the other. Bulge would be gone before I got out to look at it. Found it when someone helped push on the pedal while I looked. When pushing pedal and holding firm, pedal would creep down similar to air in lines.
2. One of the junction blocks in the line was clogged. Piece of junk would clogg when pressurized, but release in the reverse.
3. wheel cylinder corroded just enough to hang, but still release.
4. brake pads oily and cleaned. Need to replace pads at this point.

Hi, My 49 1/2ton had the same problem . When my dad had the truck he took it to a few shops to have it checked out ,nothing was found, then last year I was under the truck on jack stands doing a oil change( no creeper) I went to pull my self into another position I grabbed the tie rod and herd and felt a clunk. I found one tie rod end had play in one position, it would let the tire change toe about 1/4 inch.

Hi, a second note, today I was installing good used front springs in the truck and found that the pivot bolt and bushing on the passenger side with lots of wear(about 1/8" or more play). So my theory is that when I hit the brakes hard, the axle moved back 1/8" and the loose tie rod end(same side) let the wheel toe out and skid or lock up.

Welcome to the world of "old anything" hippy. The further into them we go the further into them we must. It just a realization that our work is never done. Good thing it's a hobby or many of us would hate it as a vocation. Stay after it, your making progress.