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.