Is knocking my shock absorber
 

On my 76 TA I am using the Hotchkis rear sport leaf springs (lowering) and their matching Fox shocks. Over 8 years. Together with the lower front-end coil over suspension and Hotchkis frame connectors things have been great and the ride not bad considering its stiffer. 18-inch wheels with 285 40s on the back. Lately I have noticed a knocking or thumping or deep rattle (hard to explain), not extreme, when I drive over some nasty roads. All good on decent roads even with minor bumps. I have checked everything (rear shackles, leaf spring plates and bushings, front leaf spring connection, axle U-bolt, sway bar connections and etc.). The axle bearings are fairly new and replaced during a Wilwood conversion. There does not seem to be anything wrong visually. When I push down on both rear fenders everything is okay. I removed a jack from the trunk even though I had it down tight. The spare tire is down tight (LOL never needed on for decades, but if I get rid of it I will get a flat). Could this be something to do with a rear shock failing. They are not adjustable and are described as tuned 1.5 street performance matched for the leafs. Thanks.

Have you considered exhaust system hangers? (If you have them)

Shock mounts on ends rubber, poly or solid? My shocks have spherical bearings on the ends and make a knocking noise in the rear.

^^^^^^^^This...if poly bushings, also check that they are greased...otherwise could make some noise.

Check all your transmission crossmember bolts and inspect the transmission mount to see if it has failed.

Thanks for the great ideas. I will check the hangers. The leaf spring pads and sway bar connection points are all poly so i will go over that. The shocks I believe are rubber mounts. Tranny mount new and cross member good but I will double check.

I had a similar knocking noise in the rear of my 71 GTO. After much frustration I found that there is a reinforcement piece between the quarter panel and package tray area. it seems to have attached to the quarter with some kind of dumdum sealant which had dried out. I filled in the gap as best I could with "Right Stuff" sealant and taped it down overnight. Noise gone! Sounded just like a tailpipe hitting the frame. I actually found it by accident while replacing the rear quarter window rollers. The front part of the reinforcement is visible through the hole.

Ha, i had that inside 1/4 panel brace do the knocking. LH-side. Easy fix.

Over the years I've found several different defects that can cause a double knock. Most times I've found them in suspension components, sway bar bushings, and shock mounts in particular cause double knocks.

I also found a trunk torsion rod disconnected one time that caused a double knock, the unlatched end came out of the sheet metal hook.

:2cents:

Thanks a ton for the suggestions. I checked all the ideas except the package tray area (will save that for after a test ride it needed). Everything was good with some exceptions (and embarrassing since I do keep the ol’ TA in top form). The nylon lock nuts on the upper and lower shackle bolts on both sides needed some significant snugging up. The axle U-bolt nuts on the leaf spring plates were good but did allow for a bit more snugging. And the lower rubber bushings on the passenger side shock needed a good amount of nut turning to get them to sandwich properly. Tied up with things but suspect and hope this solves the problem after testing. Will report back later. Crazy, even though the car does not rack up the miles these days, it was surprising how these things creep up.