Dragging rear brakes on one side

[MikeB]

After 50 miles or so of driving and stopping, especially from higher speeds, the left rear shoes on my 82 C10 start dragging. When I let off the gas to slow down, the brakes seem to lightly pulse – “grab, release, grab, release” with each revolution. Acts like a high spot on the shoes and a high spot on the drum are lining up once per revolution. I know it’s the left rear because the wheel center on that side is 40-50 degrees hotter than the right side.


However, when I get the truck up on jack stands the wheel spins freely. And if I drive the truck a few hours later, there is only a slight hint of the problem. Drums shoes, and wheel cylinders have less than 2K mile miles on them. Shoes fit the drum curvature perfectly. Rear hose is new, and the right rear is fine. I don’t know if axle bearings have ever been changed, but there is no seal leak. Pulling the drum shows nothing strange. If I back off the adjustment, the problem goes away for a while, but self-adjustment brings the shoes closer to the drum and the problem returns. I’m wondering if the brake drum is going out of round when hot. I'm very close to replacing drum, shoes, wheel cylinder and axle bearing on that side.

Any suggestions?

[SCOTI]

Originally Posted by MikeB

After 50 miles or so of driving and stopping, especially from higher speeds, the left rear shoes on my 82 C10 start dragging. When I let off the gas to slow down, the brakes seem to lightly pulse – “grab, release, grab, release” with each revolution. Acts like a high spot on the shoes and a high spot on the drum are lining up once per revolution. I know it’s the left rear because the wheel center on that side is 40-50 degrees hotter than the right side.


However, when I get the truck up on jack stands the wheel spins freely. And if I drive the truck a few hours later, there is only a slight hint of the problem. Drums shoes, and wheel cylinders have less than 2K mile miles on them. Shoes fit the drum curvature perfectly. Rear hose is new, and the right rear is fine. I don’t know if axle bearings have ever been changed, but there is no seal leak. Pulling the drum shows nothing strange. If I back off the adjustment, the problem goes away for a while, but self-adjustment brings the shoes closer to the drum and the problem returns. I’m wondering if the brake drum is going out of round when hot. I'm very close to replacing drum, shoes, wheel cylinder and axle bearing on that side.

Any suggestions?

I would first swap the drums side to side. See if the problem/heat follows the drum.

[MikeB]

Thanks. You're the fourth person to recommend that, so it's definitely worth trying!

After taking just a short drive today, I actually measured the temp at 3 places on the edges of the brake drums just outside of the backing plates. The suspect side was 80-120 degrees hotter.

[SCOTI]

Originally Posted by MikeB

Thanks. You're the fourth person to recommend that, so it's definitely worth trying!

After taking just a short drive today, I actually measured the temp at 3 places on the edges of the brake drums just outside of the backing plates. The suspect side was 80-120 degrees hotter.

Yikes.

[cadillac_al]

Did one of the pins break off?

[MikeB]

Swapped the drums from left to right and the problem followed the drum. Only thing I can think of is the drum gets out of round due to the heat generated by driving and braking. When at ambient temperature, it slides off and on the shoes easily, just like the other one. No sign of dragging on the drum or shoes.

Interesting that the "bad" drum had a lot more surface rust than the other one, even though both were the same store brand installed at the same time. Must have been from a different batch or a different Chinese communist supplier.

Just ordered a Raybestos drum from Rock Auto instead of the store brand drums at my local auto parts stores. I've always had good luck with Raybestos and Wagner, no matter where they are made.

[SCOTI]

Originally Posted by MikeB

Swapped the drums from left to right and the problem followed the drum. Only thing I can think of is the drum gets out of round due to the heat generated by driving and braking. When at ambient temperature, it slides off and on the shoes easily, just like the other one. No sign of dragging on the drum or shoes.

Interesting that the "bad" drum had a lot more surface rust than the other one, even though both were the same store brand installed at the same time. Must have been from a different batch or a different Chinese communist supplier.

Just ordered a Raybestos drum from Rock Auto instead of the store brand drums at my local auto parts stores. I've always had good luck with Raybestos and Wagner, no matter where they are made.

Very odd indeed. I try to use only Wagner or Raybestos when/if possible. Sometimes it's just not financially...

[MikeB]

I was going through my old posts, and wanted to close out this one. I put around 500-600 miles on the truck after installing the new drum, with no more problems. So that old drum had some kind of defect. Must have been a poor casting causing it to deform when hot.

Ended up selling the truck late last year, knowing there wouldn't be any surprises for the new owner.

[SCOTI]

Thanks for the follow-up. It definitely can help others w/similar issues & from someone who tries to help others here when I can, it's appreciated to hear/learn of a resolution.

[LT7A]

This is good info. I had a very similar problem on my first squarebody, years ago. Went through much of the same troubleshooting process you did including having the drum turned. Never occurred to me that it might be the drum itself. Makes perfect sense. I'm glad there are people here that have ideas that are better than mine.