why are my brakes locking on me?

[drewfever1020]

i got a new master cylinder and change out my drum brakes and i tried bleeding them, but still no improvement!
it seems like theres more pressure going to the right rear than the left!
its my right rear that locks on me, what can it be?

[Painter D]

Sounds like the proportioning valve.

[drewfever1020]

i was thinking the same thing, does it control the pressure?

[Painter D]

Yes, it controls pressure. I just reread your first post ,if it's just the right rear thats locking up I would check the wheel cylinder to see if it's working properly.

[Longhorn Man]

no
That truck doesn't even have a proportioning valve... just a distibution valve, and that only forks front to rear, not side to side.
You either have shoes out of adjustment, or there is fluid (axle oil or brake fluid) contaminating a drum.

[drewfever1020]

i have a 71 and it does have a proportioning valve!
and my cylinders are good cuz i got new ones!

[mrein3]

If your right rear is locking, check your left rear. Like longhornman said you could be leaking brake fluid or rear end grease into the drum on the LEFT side. What could be happening is that you sense a lack of brakes so you press harder. If the left has grease or brake fluid in it it won't catch while the other side will.

[drewfever1020]

my left brakes good its just that the right brakes before it causing it to act like its locking up!

[Longhorn Man]

ok, a 71 does have a proportioning valve... you never mentioned anything about discks or any of that... just said you chainged out your drum brakes.
So the proportioning valve still only proportions front to rear, not side to side.
Since you were just in there, we will assume you have no oil or brake fluid.
You may have a pinched line going to the left wheel
you may have way out of adjustment on the left wheel

[1956cameo]

I would agree with Andy that one of your rear brakes are "pulled in" more than the other, causing only one to lock up. I would take off the rear hubs and adjust the brake pads until the hubs lightly touch the pads when put back on. Also if there is two rubber lines for the back brakes one of them could be old and swollen inside. This is assuming that there are two lines and that they are old.

[Longhorn Man]

also is there a chance that you put both big shoes on one wheel, and both short shoes on the other wheel?

[Tx Firefighter]

I've adjusted a lot of brakes in my time. I always turn the adjuster down to where the brake is locked and the adjuster won't turn anymore. Then back them off about 10 clicks per side.

This centers the shoes in the drum much better.

If that doesn't do it for you, you have an air bubble in the right cylinder or you have contaminated shoes or drums.

The prop valve controls front and rear, not side to side.

[Sinister]

If you replaced the spring kit on one side and not the other it'll do this as well. Don't ask me how I know.

[Stock72c10]

When I replaced mine the adjuster was rusted solid. Did you check it to make sure all the adjuster parts were moving freely when you changed the shoes (there are three parts)?

[Rons86]

Check your emerg. brake cable. Had one do the same thing and a cable had frozend causing one side of brakes to be out ouf ballance.