Right Rear Drum Brake issue has everyone stumped

[Bacca]

I have had three different shops work on by right rear brake issue. 1st shop was a mistake on my part. 2nd & 3rd shops both ASE certified and well established in the neighborhood. I have a 1982 SWB. It came with a 4.1 automatic and disc frt. & drum rear. Every part that i could get has been replaced TWICE. OE when available and the best A/market I could find for all the rest. Drums, Shoes, Hardware, Wheel Cylinders have been replaced except the backing plate & the rear axle seals. E-Brake completely removed. Tried at least four A/market drums none worked. All bottomed out on the backing plate causing a bind. Ended up turning the original (I think it's original) drum and running it. Now the wheel gets pretty hot when driving. Every brake part Frt/Rear has been replaced including the Master/Booster. All steel lines are original and have good flow for bleeding. Near as I tell this truck never had a proportioning valve. I can't work on my truck anymore due to an arm injury but both shops allowed me to observe the repairs and their honest attempt at fixing it. I have countless drum brake repairs myself and I'm the first guy to say this "shouldn't be that hard" but here I am. Thanks in advance

[kipps]

I assume you've replaced the brake hoses?

Every truck came out of the factory with a proportioning valve. It's mounted directly below the radiator. If that's been removed and replaced with a couple of tee fittings, that could possibly be causing this.

[mongocanfly]

If you had 4 different drums bottom out on the backing plate , that narrows it down..
Is the backing plate bent,?... how much end play does the axle have... is the bearing worn?
.I'd pull the axle out and look at it..especially the c clip area...
.if your thinking the brakes are dragging, did you replace the brakes lines? Rubber lines are notorious for interior breakdowns and acting like check valves...

[kwmech]

Prop valve on these trucks are down on the front x-member below the radiator. Bad valve would affect both sides. What engine is in this truck? If I remember correctly the diesel/big block trucks had wider brake shoes and drums. AND how were the brakes before you started all of this. Pics of the assy with the drums off.

[Palf70Step]

Yep there are 2 sizes drums. I know 6 bangers uysed the narrower (2" I think). Not sure what ones had the wider wether iut was all V8 or just some options. AS mentioned, your proportioning valve is hidden to normal folks up on the from cross member near radiator.. I agree that maybe you might have a bent or messed up backing platye from the sounds of it, if they gave you the correct 6 cylinder drums.

[MikeB]

Originally Posted by Bacca

Tried at least four A/market drums none worked. All bottomed out on the backing plate causing a bind.

So, you're saying the brake drum rubs the backing plate and binds. Could it be as simple as the backing plate being bent? Probably a long shot, but how about an axle that's a little too short? Never know if a PO might have replaced it with a improperly made aftermarket axle.

I'd measure the distance from axle flange (where the wheels mount) to a spot on the backing plate on left and right sides. And I'd probably remove the diff cover and take a look at the axle ends and C-clips as suggested above.

There's something not right there. Bet I could find it in a couple hours, but charging brake parts won't fix it.

[superchevy]

at this point, maybe do a disk brake conversion

[Bacca]

Originally Posted by kipps

I assume you've replaced the brake hoses?

Every truck came out of the factory with a proportioning valve. It's mounted directly below the radiator. If that's been removed and replaced with a couple of tee fittings, that could possibly be causing this.

Thanks everyone I looked everywhere underneath and could not find a portioning valve or where one might have been. I will take another look to be sure. I was under the impression that not all squares had one. The original used drum does spin fine when the wheel is bolted on. I'm confident saying it's not the backing plate. The only non replaced part on the complete system is the original steel lines and of course the old rear drum. The reason for replacement in the first place was just normal upkeep and upgrades or so I thought. Other than fronts being about 60% worn out there was NO issues.

[MikeB]

Originally Posted by Bacca

Thanks everyone I looked everywhere underneath and could not find a portioning valve or where one might have been. I will take another look to be sure. I was under the impression that not all squares had one.

Yes, your 82 had a proportioning valve from the factory. Both steel lines from the master cylinder run directly to it. There is also an electrical wire from the front light bundle that runs to the valve's pressure balance switch, so technically it's a combination valve.

But I'm confused. Didn't you say your problem is the brake drum rubbing the backing plate? If that's the case, it's a mechanical problem, not hydraulic.
Please better explain your symptoms. Thanks.

[mongocanfly]

Try one of the drums that dont work on the left side and see if it rubs there...or swap drums side2side and see what happens

[Nick_R_23]

Originally Posted by MikeB

But I'm confused. Didn't you say your problem is the brake drum rubbing the backing plate? If that's the case, it's a mechanical problem, not hydraulic.
Please better explain your symptoms. Thanks.

This. There is a mechanical issue causing a clearance problem from the sound of things. If this was my truck, I would remove the rear axle cover and inspect the cross pin, axle shaft, and C-clip for abnormal wear, if the drum has enough inward movement to contact the dust cover. Also, is the drum seating on the axle shaft flange completely, or does it contact the dust cover first?