Brake wizards needed - I'm about to go nuts!

[joeydurango]

Fellers, I have a mystery on my hands. Any brake wizards out there to help solve it? I have spent hours looking at posts here with no solution.

For years, my 72 K10's brakes have worked well, quietly, no issues. Last fall the right rear drum brake began squealing loudly when applied at mid-pressure. Light or hard applications don't provoke the squeal. It is clearly a cyclical sound at very slow speeds, so it seems obviously related to the rotation of the drum.

1) I pulled both drums off - pads were old but still had life. Steel wooled the drums, sanded the pads - the squeal persisted.

2) Looked for cylinder leaks, they were dry. Inspected the drums for signs of some contact with anything other than the pads. Nothing. Inspected the backing plates, pads, all hardware for signs of abnormal contact. Nothing, nothing at all.

3) The drums are different, someone replaced one or both in the last 52 years, but they ended up slightly different. Swapped the drums left to right. Squeal remains, BUT STILL ON THE RIGHT SIDE.

4) Installed new pads and hardware (both sides). Squeal remains.

5) Had both drums turned. Squeal remains.

I am well and thoroughly stumped. I have a single-side brake squeal that persists through pad and hardware changes, L-to-R drum swaps, and drum resurfacing. There is no cyclical friction wear pattern on any part beyond the braking surfaces themselves. Clearly the brake is still operating - if it weren't, the squeal would be constant or not at all. The brakes were quiet for years and nothing has visibly changed.

Next step I can try is new drums altogether, but that feels like throwing money at the problem and I can't see how that would be different than the freshly-turned drums I have.

Only other thing I can even imagine is pretty out there - wheel bearing with just enough play that brake application changes wheel alignment enough to create some sort of squeal on that side. (???) But in this respect both wheels feel about the same.

What am I missing? Starting to feel insane on this one.

[Dashman]

Sorry no wizard here, but I'm sure you'll get one.

Did you inspect the backing plate areas where the shoes make contact? ...and did you add grease? What about adding grease to the anchor pin? ...was there any wear on the anchor pin?

Did you compare both sides to each other? ...like the backing plate wear, and the axle play?

Could you feel excessive play in the axle? What about the oil level in the differential? Could that have caused your bearings to go dry? After 52 years, maybe it's time for new axles or new bearing surface welded on and machined.

Good luck!

[joeydurango]

Yes, backing plate contact areas looked similar and normal, and yes, I greased them.

Cleaned and greased the anchor posts - no wear.

Yes, compared sides for wear patterns and axle play - no appreciable differences. No excessive play in the axle that I could tell.

Diff had good oil in it and has been full (I check periodically); at the same time as this brake job I did replace the gasket and refill with fresh gear oil (old gasket was beginning to seep). However the noise began months before gasket replacement and there's no change with fresh oil.

[geezer#99]

Assuming leaf springs, have you looked at the spring packs?
Or the u-bolts and spring eye bushings.

[HO455]

You might check to see if the axles are running straight and true. A wobble of the drum caused by a bent axle or a drum that's not running true will cause the brake components to move around on the backing plate with every revolution.

[A1971Blazer]

a squeal is usually a sign of a bad wheel bearing...in my experience anyway.
I can't think of a drum brake component that would cause a squealing noise
that usually has a dragging/grinding noise.
Is it only when you apply the brakes?

[joeydurango]

Originally Posted by geezer#99

Assuming leaf springs, have you looked at the spring packs?
Or the u-bolts and spring eye bushings.

I have not! What do you suspect would cause a cyclical squeal while braking? Open to looking at anything, I just want to understand what you're considering.

[joeydurango]

Originally Posted by HO455

You might check to see if the axles are running straight and true. A wobble of the drum caused by a bent axle or a drum that's not running true will cause the brake components to move around on the backing plate with every revolution.

I can recheck. Can't be the drum, as I swapped them side to side and the same side still squealed under braking. But I'll double-check the axle. Thank you!

[joeydurango]

Originally Posted by A1971Blazer

a squeal is usually a sign of a bad wheel bearing...in my experience anyway.
I can't think of a drum brake component that would cause a squealing noise
that usually has a dragging/grinding noise.
Is it only when you apply the brakes?

Thanks! Yes, only when the brakes are applied - and only under intermediate braking. Light or firm application of the pedal keeps things quiet. It's pretty clearly a brake noise, or sure seems to be - if I ease up on the pedal from a complete stop so that the truck inches forward, I can get a "stutter-squeal" from that right rear brake.

I would expect a dragging/grinding noise from metal on metal. Maybe I'll have to get a video with the squeal so you all can hear what I'm talking about.

[joeydurango]

I appreciate the replies so far - I'll pull the drums off again and doublecheck axles, bearings, and suspension components.

[geezer#99]

Originally Posted by joeydurango

I have not! What do you suspect would cause a cyclical squeal while braking? Open to looking at anything, I just want to understand what you're considering.

Cracked leaf.
Loose u-bolts.
Missing anti rattle clips.
The liner between leafs missing.

[Steeveedee]

I had this on an Astrovan and tried what you have done. Try swapping shoes side to side; if that doesn't work put on new shoes.

[RichardJ]

>> if I ease up on the pedal from a complete stop so that the truck inches forward, I can get a "stutter-squeal<<

Are you absolutely sure the sound is coming from the rear? Have you had someone in the pass seat verify, with window up/down, the sound is from the rear?

Easing up on the pedal at a stop may be allowing the metering valve to hold back the pressure to the front disc brakes allowing the front rotors to roll slightly until the rear can take complete control of braking.
The Metering valve in the combination valve may have a threshold pressure of 50-80 psi., depending on combination valve specs Any pressure below that means only the rear brakes will be engaged.

[raggedjim]

I'm sure you probably checked for this but is there any chance the outer lip of the backing plate is rubbing on the drum? I had one that was bent at the edge and it made a high pitched squealing noise.

Good luck, Rg

[joeydurango]

Originally Posted by raggedjim

I'm sure you probably checked for this but is there any chance the outer lip of the backing plate is rubbing on the drum? I had one that was bent at the edge and it made a high pitched squealing noise.

Good luck, Rg

Yep, I checked that - but thanks for the idea anyway. Haven't had a chance to even look at the truck this week. Going to check the wheel bearings more closely as soon as I have a few minutes. That's currently my leading hypothesis. As much as I don't want to swap 'em (or learn the condition of the axle shafts ), at least it would be something identifiable and reparable and I could be done with this!

[joeydurango]

Originally Posted by Steeveedee

I had this on an Astrovan and tried what you have done. Try swapping shoes side to side; if that doesn't work put on new shoes.

As noted, new shoes already installed.

[joeydurango]

Originally Posted by RichardJ

>> if I ease up on the pedal from a complete stop so that the truck inches forward, I can get a "stutter-squeal<<

Are you absolutely sure the sound is coming from the rear? Have you had someone in the pass seat verify, with window up/down, the sound is from the rear?

Yep, had a passenger verify location.