Mechanics

CHEVY REAR DRUM BRAKES

1989 Chevrolet Caprice

Brakes problem
1989 Chevy Caprice V8 Two Wheel Drive Automatic 80000 miles

my rear drum brakes backing plate is bent because the brake shoes and wheel cylinder were torn off the backing plate. Everything seemed to be hooked up right until you use the brakes. What could be causing this to happen
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Lucas masters
August 22, 2010.



Hi lucas masters. Welcome to the forum. If you have the wheel cylinder that is held on with a big metal ring with two fingers, the hour glass-shaped hole in the backing plate corrodes away allowing the wheel cylinder to rotate. The dealer has an updated backing plate available that uses a normal bolt-on wheel cylinder like everyone else. That backing plate might be available now from the auto parts stores too.

Caradiodoc

Caradiodoc
Aug 22, 2010.
I already bought the new backing plate with the bolt on wheel cylinder and it is completely ripping the two bolts out of the back of the wheel cylinder as well as the mounting pin that holds the brake shoes in place that is located right above the wheel cylinder. It completely distorts the backing plate and oblongs the holes every time I put it back together. I welded the wheel cylinder in place as well as the pin above it and has yet to brake but it only a matter of time because something is putting a lot of pressure on the shoes. The only thing I have yet to replace is the drum. The whole emergency adjuster and arm and components and springs and shoes are all new. Wheel cylinder pin and backing plate as well. I also just mounted and balanced two new rear tires. I noticed at the junkyard when I was getting a stock backing plate that the drum had a quarter sized led weight or spacer about a 1/4 inch thick between the outside of the drum and between the rim. Is that an old fashion way to balance the drum or is that needed to cushion the pressure the wheel puts on the drum

Tiny
Lucas masters
Aug 28, 2010.
I've seen that weight of which you speak and always dismissed them as a balancing weight. I can't imagine what would cause the kind of damage you're describing. To tear the backing plate is way more than the typical rotating wheel cylinder. The only other suggestion I have is to be sure the parking brake cable isn't sticking and holding the shoes away from that big anchor pin on top. You should be able to push the parking brake strut bar a good 1/8" against the pressure of the anti-rattle spring. If a sticking cable is causing the shoes to be held away from the anchor pin, the shock from when they grab the drum might be what's pounding the backing plate apart. Even that would be unexpected as it happens to a lot of cars without tearing it up. Gee whiz, tires lock up and skid all the time without causing that kind of trouble.

Shoes will grab real hard too if they're contaminated with gear lube from a leaking axle seal. Same thing though; that too shouldn't cause the kind of damage you're getting.

Caradiodoc
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Caradiodoc
Aug 28, 2010.

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