Please help me diagnose...

Noticed when backing up if I press and release the brakes, as soon as I release them I get a pop-clunk noise. It feels like I let off the brake and then the caliper suddenly releases pressure on the pads rather than gradually. I don't think that's necessarily what is happening, but that's what it feels like. I can feel the clunk both through the pedal and the whole car. Only when in reverse, doing the same while moving forward makes no noise. Was thinking it could be a rear drum issue but it really sounds/feels like it's coming from the front.

TIA

Mine started this and is now to the point that on wet roads while coming to stop I have a clunk while braking. I believe it has to do with the arms, my arms are tight but my upper bushings aren't in the best shape.

A common problem with a clunk when braking or letting off the brakes and accelerating is that the slip yoke needs to be greased. Both front and rear.

Check your brake shoes. Drum brakes bind in reverse when shoes are worn or out of adjustment.

x2

After you check your brakes, take a look at your upper and lower control arm bushings. If you lay in front of the vehicle and have someone inside put it in reverse and apply the brakes look for the differential shifting. I had a similar clunk before and replaceing the bushings on my axle side of the upper control arms took care of the issue.

Brian nailed it. Replaced the bushings and clunk is gone. Also doesn't squirm around driving down the road anymore. Thanks!