Brake problems, and a question

[68Coupe289]

My front right drum (manual, on a 68 Mustang) is locking up under any braking condition (light or heavy), and remains locked up for 3-5 seconds after I release the pedal.

I know there isn't much to brakes, and I'll be tearing into it this weekend (hopefully). Just curious what you all thought the problem will be.

Proportioning valve, or wheel cylinder (or other).

I'm betting prop. valve, which leads to one other question: Is the Prop valve on a 4 wheel manual drum car the same as the one on a power front disk car? If it is, then I already have a replacement part in the pile of disk brake parts from a loaner car that I have yet to install.

Let me know. Thanks everyone.

 

[mustang70]

I'm pretty sure there's no proportioning valve on drum brake cars. I would check the wheel cylinder and the springs. They may be worn out and not able to hold against the cylinder.

 

[71vert-pga]

The front drum cars just use a distribution block which is more or less a fancy double T. I don't believe it has any ability to regulate or "proportion" pressure from front to back.

 

[68Coupe289]

I'm calling the distribution block the wrong thing. I was talking about the distribution block when I said proportioning valve.

So are the distribution blocks the same? And could it cause the problem?

 

[Hack]

I'm pretty sure there's no proportioning valve on drum brake cars. I would check the wheel cylinder and the springs. They may be worn out and not able to hold against the cylinder.

This is the first thing that occurred to me as well. If the springs look ancient, I think you should start by replacing them. Spring kits are pretty cheap IIRC. Well, drum wheel cylinders are pretty cheap too.

Remember that drums are self-actuating (I think that's the term. )
When you apply drum brakes while the car is moving forward, the geometry of the drum brake mechanism is such that the car's resistance to the brakes actually forces the brakes to lock more tightly.
I don't feel like I explained that very well, but the crux is this: the drums may lock when used while the car is moving, but not appear to have any problems when the car is stationary.

One other thing, unless you're a drum brake expert.. do one wheel at a time! I had to look at another wheel several times the last time I replaced spring kits. But then again I'm not always the brightest bulb.

 

[2nd Mustang]

I will bet binding piston in wheel cylinder, OR brake shoes rubbing on backing plate, OR out of round drum and worn shoes (had this happen on an off road bug, the only way I could release it was hitting the drum with a hammer!). I don't think it would be the distribution block as it only distributes, it doesn't regulate pressure, but then if I was smarter........................

 

[67GTFastback]

I will bet on the springs. The brake fluid is pushed to the wheel cylinder when the brakes are applied. As soon as they are released, the springs pull the shoes back forcing the brake fluid to retract in the lines to master cylinder. The other thing I would look at is the brake pedal, is it sticking to the floor or does it release properly? If it releases properly, I would definitely start with the springs. Good luck and let us know how it turns out.

 

[71vert-pga]

New wheel cylinders are about 12 bucks. Swap 'em and be done. That way you don't have to worry about springs and crap like that. It doesn't get much easier.

 

[Mustang Jim]

I, too, would bet that it's the springs causing the problem. They are easily and quickly replaced and the cost is minimal. My second bet would be a binding wheel cylinder. Also, grease the backing plate at the touch points in case the shoes are binding against it. How old is the brake hardware? As it is likely that the hardware is the same age on the remaining wheels, maybe it's time for some freshening up all around. I hope this helps.

 

[Hack]

Also, grease the backing plate at the touch points in case the shoes are binding against it. How old is the brake hardware? As it is likely that the hardware is the same age on the remaining wheels, maybe it's time for some freshening up all around. I hope this helps.

I completely agree. Good points all. Brakes are not something to skimp on.

Just think, if you crash into someone/something - damage to your car is the least of your worries. People get hurt and killed all the time in car accidents, and you don't want that on your conscience.

 

[mozpony]

you should check for binding at the master cylinder push rod,or it could be missadjusted

 

[WORTH]

Don't overlook the obvious, a drum brake that is out of adjustment will jam the front show and not want to release. Could just be out of adjustment.