Rear Brakes - Loud rubbing/scraping noise??

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92GMCK2500

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Problem:
Loud scraping noise coming from rear brakes under moderate braking. Noise is worse on pass/right side. I touched the drums and rims when i got home to see what was going on, they were too hot to touch after driving for an hour, like real hot! Not good.

Conditions:
Usually under load/force, going downhill with the camper loaded up, #9000 of weight coming to a stop. Seems random, happens 70% of the time. Not so much when braking light or heavy. Noise only started after driving 50kms distance.

Info:
11" drums, duo servo, recently rebuilt, including all new hardware, wheel cylinders, shoes, drums, SS brakes lines. I've also replaced the wheel bearings, seals and axle shaft C clips.

I re-used the original backing plates, sanded down the shoe contact points smooth again as they had gouged out real bad.

Adjusted brakes following GM service manual including reversing the truck back and forth a dozen times to active the self adjusters. I've greased shoe contact points.

Suspicions:
1. Drum and backing plate scraping somehow? Not square or 'true' to each other.
2. Backing plate issue, shoe contact points sanded down too much, now causing poor shoe to drum contact?
3. Over adjusted brakes, too tight? Shoes dragging? Hence heat. But why noise?


I am real stumped on this one, been chasing the problem for awhile now.

Any ideas??

Guess it might be the case of going back through everything again to double check my work. Cheers
 

454cid

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Problem:
Loud scraping noise coming from rear brakes under moderate braking. Noise is worse on pass/right side. I touched the drums and rims when i got home to see what was going on, they were too hot to touch after driving for an hour, like real hot! Not good.

Sticky parking brake cable, would be my guess. That's why my brakes got hot after being rebuilt by a shop many years ago.
 

Chevy-SS

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Jack up wheels and try to rotate by hand. There should be slight drag, but only slight. Brakes should never get really hot, unless you've just slowed down a heavy load on a big hill. If they're getting hot under normal use, then something is dragging. It should become self-evident which wheel after you try rotating by hand. Don't put it off, jack 'em up and try rotating.
 

thinger2

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Had a similiar problem awhile back and it was caused by a huge burr on the shoe frame.
Even though I had sanded the backing plate grooves smooth the burr edge ate right back into it.
This might be hard to see but if you look close the shoe has cracked from the heat and is worn uneven and glazed from it being cockeyed while it hangs
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The entire shoe has those little heat cracks.
I ended up welding and grinding the grooves in the backing plate while it was still on the truck.
You can do that you just need to be carefull about heat so you dont warp it or cook the axle seal.
It can be done.
And I always file the burrs off of brake shoes and pads
 

92GMCK2500

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Jack up wheels and try to rotate by hand. There should be slight drag, but only slight. Brakes should never get really hot, unless you've just slowed down a heavy load on a big hill. If they're getting hot under normal use, then something is dragging. It should become self-evident which wheel after you try rotating by hand. Don't put it off, jack 'em up and try rotating.

Thanks. I am having trouble with the 'slight drag' part. When rotating the drum by hand the drum seems to drag more so in one spot of the rotation than other spots. E.g. For 1/8-1/4 of the turn, it requires more human muscle force to turn the drum. In other spots, its an easy 'slight drag' turn and relatively easy to turn by hand.

What could be causing this?
 

92GMCK2500

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And I always file the burrs off of brake shoes and pads

Thanks for this ^ tip. Its worth inspecting and I might as well file out the shoe steel frame/plate to eliminate the potential burr problem.

If I'm understanding you right, you're saying you weld on new material onto the backing plate to gain the 'fat' back and grind it smooth again as its meant to be originally/new condition?

I've listed my suspicions in my OP. All calculated guesses at this stage. Interesting to hear others experiences. Cheers.
 

92GMCK2500

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Could be warped

Clarify. The drum? Backing plate? shoes?

Drums are new. Raybestos R-Line. Possible, but not likely.
Shoes are new. Centric Heavy Duty part #11204730.
Backing plate - Originals. Warped, maybe? Anyone heard of this actually happening?
 

SUBURBAN5

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Clarify. The drum? Backing plate? shoes?

Drums are new. Raybestos R-Line. Possible, but not likely.
Shoes are new. Centric Heavy Duty part #11204730.
Backing plate - Originals. Warped, maybe? Anyone heard of this actually happening?

I would think drums. Normally you should be able to spin it and the resistance is the same. If you spin it and it drags a little then frees up then drags. That makes it should like something not perfect circle.
 
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