Diagnostic assistance request: rear suspension clunk

This may not be your problem but its a start to check. Was your car originally equiped with a 7 1/4 rear . If so the housing bump stops are shorter for a 8 1/4 and a 8 3/4.

Are your leaf spring shackles angled back to far from the flatter leafs. This causes the spring shackle to hit the bracket support. They make a Z style shackle to eliminate this issue. If they are against the bracket they will knock on accelaration and deccelaration with spring wrap. I have notched the support in the past. It will be the inner shackle bar hitting.

You checked the diff and drive shaft slop so you can eliminate that.

The correct Diameter bolt in the front eye. Early cars pre-72 have a smaller 1/2" diameter. 73 and later have a 9/16 bolt. Using the earlier spring eye with the later spring mount could be another problem.

Make sure your axle bearing adjustment is correct if using tapered bearings

If you are using the green bearing style the removal of the axle adjustment separator is required. or you must have the axles cut if using a unit that is not removable such as the alburn/cone style unless disassembled.

Check your rear bushings. some of the poly bushing don't last long at all.

Again these are just some things to check that I have run into over the years that create problems. I do not know your car so they might not pertain to your issues.

There may be members such as "Yellow fish with no teeth just lips" that will find issues with something I am saying. He always does. Don't mind him. He has problems with everything myself and some other members say. He is just here to cause conflicts with those he don't like because he don't like being reminded of how little he knows . Or he is just jealous that he only has Tonka's to play with.

Good luck, Steve