Knocking from rear end

[SignalHill]

I’ve got a 1990 GMC C1500. 132,000 miles. Recently I noticed a bumping sensation in the brake pedal when coming to a stop. The bumping corresponds to the speed of the vehicle and stops if I let off the brakes. It’s gotten worse, and if I roll down the window I can hear a knocking from the rear end somewhere that goes along with the bump in the brake pedal. The truck kind of surges after the knock, as if the shoes are making it over a hump and then free to spin again.

This truck belonged to my mom before I got it. The rear brake assemblies appear to be in good shape. Shoes are fairly new. The drums are grooved, but not cracked or bumpy in any way.

Also, when the truck sits overnight the brakes work super smooth the first few stops, then the issue starts to show up.

Where do I look next? Any other relevant info I’ve left out?

 

[Schurkey]

JN/JB5 brakes? 8.5" rear axle?

Photos of the shoes, as installed on the vehicle?

Photos of the braking surface of the drums? Drums contaminated with brake fluid or axle lube?

What are the condition of the axle bearings and axle shafts?

When you remove the axle cover to pop the C-clips out so you can inspect the axle shafts 'n' bearings, you can also verify the gears within the differential. However, based on symptoms, this isn't a differential issue.