Grigg. Sorry nope! I pulled the rear bumper off although it was tight. There are no missing rivets and all the bolts are tight. I have tried pulling, pushing, using a pry bar underneath and everything is snug. This is why I am so frustrated trying to find it. The only thing which is different is that there is a worn groove in the e-brake cross shaft where that crescent shaped bracket rides it. The bracket is right by the clevis for the linkage from the e-brake pedal.
At the moment there is about less than 1/8" clearance between them.
I mentioned looking at the forward part of the chassis. I know I have a slightly worn king pins and wonder if that could be making that thumping. Apart from that the front suspension is good and when I hit those bumps the steering wheel does not rip out of my hands nor does the truck jump around. But I have been told that worn king pins do not make that kind of noise.
I should also mention that there is a small crack in the top of one of those curved skirts that are bolted between the bed and the running boards. Looks like it cracked from being pushed down. I painted them recently and the crack was not there. There is ample clearance between the bed bottom and cab corner so they are not touching. But again one of the things I did during my checks was to remove the skirts to see if it made a difference. It didn't.
