[-SS454-]

The right rear wheel keeps locking up under hard braking. Typically I've read this is a common symptom of a leaking wheel cylinder. I've pulled the drum and I can't see any leaks. How much of a leak would cause this? I thought it was the fluid contamination on the shoes. I again see no visual signs of a contaminated shoe, though I have no reference to what bad looks like. Ive read on vehicles such as jeep cherokees where the parking brake gets stuck or something and causes this issue? How does one check for this?

Any help would be appreciated. Thanks

 

[Alan F]

I'd start with a visual inspection of both sides to make sure that the shoes are wearing properly and all the parts are there and functioning properly, to include the auto adjuster mechanisms and parking brake. Then, I'd make sure that both sides are adjusted uniformly. Then I'd clean the shoes and drums. Also assuming no brake fluid or rear end fluid leaks, I'd go stomp it again.

 

[novaderrik]

do a few hard stops in reverse and see if that fixes the problems...

 

[OLDED]

Also, check for a ding in the crossover line on the differential - maybe road debris has hit it. Bleed both sides to see if you are getting fluid equally to both sides. Could the car have had a wheel cylinder replaced previously and that episode have contaminated the shoes on that wheel? FWIW

 

[-SS454-]

well i popped both sides off today. Brake shoes have a lot of pad on them, the springs and other components inside the drum appear to be in newer shape. Wheel cylinders are dry on both sides. I applied some anti-seize on the slider points and cleaned everything up with cleaner. Upon further inspection I found the left side (the side that doesn't lock up) the adjuster clicker piece isn't making contact with the teeth on the adjuster wheel. Also the if I wiggle the parking brake cable it moves the metal piece (parking brake arm?) that its connected to quite a bit. This is not the case on the side that locks up. Everything is snug, the adjuster plate contacts the teeth. If I pull on the parking brake I can even see it moving the spring loaded divider between the shoes. I don't know if the left side or right side is correct.

I did find that the axle seals have leaked a little bit of fluid, but nothing that has splattered around created dampness inside the drum.

 

[JWagner]

Is this a recently arrived problem? If so, it is likely a contamination issue with either oil or brake fluid. It can also be an out of round drum. If you swap the drums side for side and the lockup moves to the other side, that would be a strong indication of a drum that needs to be turned. A long shot would be that someone replaced the cylinders and got two different bore diameters.

 

[-SS454-]

nope not new. Ever since I got the car it would lock a wheel.

 

[JWagner]

Time to swap the drums.

 

[OLDED]

Get the auto adjusters and parking brake adjustments right first - that may be the whole issue. Be sure the parking brake cables are freely moving, they may be hanging the brake shoe movements if frozen which is common 40 yr. old cars. Keep an eye on the seeping axle seals regularly - they can start leaking quickly once they begin to seep - that requires all new brake shoes when it happens.

 

[Andy's Auto Repair]

And make sure you have no excessive axle bearing play. It should go around .010 in and out, but no more than .001 up and down.

 

[-SS454-]

I think there is more than 0.010" axle play. Id guess it was closer to 1/32". I am quite worried about there being excessive wear on the axles. Starting to sound like i need to change seals, possibly bearings, wheel cylinders, and shoes. Possibly the entire drum.

This is depressing since I really don't want to spend a whole lot of money on this 12 bolt/drum assembly as I plan to upgrade to a Moser 12 bolt with discs.

 

[Schurkey]

Often overlooked--or outright screwed-up:

Adjust the service brakes using the star-wheel and lever mechanism BEFORE adjusting the park brake.

Loose service brake adjustment CANNOT be compensated with by the park brake adjustment--but lots of folks do exactly that. Once the park brake is adjusted too tight to "compensate" for a loose service brake adjustment, the shoes don't seat on the anchor-pin, instead they're held apart by the park brake strut. This does not work properly.

The shoes M-U-S-T rest against the anchor-pin when not applied.

 

[-SS454-]

what part is the anchor-pin and what part is the park brake strut?

 

[CoolBlueGlow]

If, as you said, you've had the problem "since you had the car", is it possible that the leading and trailing shoes are that side are installed backwards?

In spite of what is often reported on the internet, in forums, and on car talk radio shows, etc., according to GM / Chevrolet service manuals, the leading shoe has the short lining. (e.g. This, according to GM 1966 sec 5-13, item 7, etc.)

Also, be aware that drum brake lining are eccentric by design. This eccentricity is not well understood by many technicians, and is vital to smooth brake operation. In a drum brake, the center of the lining first contacts the drum. Additional hydraulic pressure slightly deforms the shoe, engaging additional shoe surface. Again, this need for eccentricity is not well understood by a many folks, who simply presume that the entire shoe contacts the drum and that hydraulic pressure directly modulates stopping power. That is not true for drums. Drum shoes' braking force is amplified by the rotational force of the drum. Without some means of varying the percentage of shoe surface engagement, drum brakes would be "off/on" devices...which we call "grabbing brakes".

Therefore, The percentage of effective shoe surface engagement is modulated by the hydraulic pressure applied by the cylinder. Coupled with the eccentricity of the shoe, this is what provides variable stopping power on drum brakes.

Remove the linings and drum. Hand fit the linings into the drum on your workbench and examine them for slight eccentricity relative to the drum. Linings which do not exhibit sufficient / any eccentricity relative to the drum are highly prone to grabbing symptoms.

Here's a more thorough explanation, with pictures. See Pg. 9 at

http://www.autoshop101.com/forms/brake03.pdf

Also, remember that the star wheels are L/R sensitive, and are so labeled. They are easy to get wrong. Correct adjuster operation is critical, as noted by others.

Finally, I have seen it happen where a car ends up with two leading shoes on one side and two trailing shoes on the other, due to the carelessness of the technician installing the shoes. A mixup on the bench results in the shoes getting jumbled together. This is also bound to cause problems.

Just some things to check

 

[-SS454-]

Shoe's are installed correctly. That looks like a great PDF, I will have to give that a read. Thank you!

 

[LeoP]

Actually, if there is fluid contamination or gear oil contamination, that side will usually not lock up. It sounds like an adjustment/self adjuster problem to me, solve that so the shoes adjust equally and you'll most likely fix the problem. If nothing is leaking, leave the seals,bearings, etc alone.

 

[-SS454-]

Actually, if there is fluid contamination or gear oil contamination, that side will usually not lock up. It sounds like an adjustment/self adjuster problem to me, solve that so the shoes adjust equally and you'll most likely fix the problem. If nothing is leaking, leave the seals,bearings, etc alone.

The axle seals do leak, just not very badly. I am going to attempt to change those seals, wheel cylinders, and brake shoes. I also think I will loosen the parking brake adjuster, then re-adjust the drum brakes and then go back to the parking brake just to be sure as well.

 

[SethT]

You just need to adjust the adjustment star. Back it off a turn or two, adn see if it still happens.

 

[-SS454-]

You just need to adjust the adjustment star. Back it off a turn or two, adn see if it still happens.

I backed it off a bunch of turns and still locks up.

 

[LeoP]

Are both rear whl cylinders working?