Yesterday I finished installing my new rear leaf springs, 4.5 mid eye. I took it out fora drive and I now have a very large thunking noise when I let off of the gas or am upshifting. It is always at the transition between gears or when I stop accelerating. I just got under and checked and everything LOOKS ok, the spring plates are seated and nothing is loose. Anyone know the possible source of my ailment? Is it possible that I have the shackles tightened down too tight therefore preventing good articulation of the leaves and rear? The car is a 1965 coupe, inline 6, 4 speed.

 

u joints tight??

 

Yes, U joint is good. I completed 1 leaf spring a while ago and have drove it since with no issues. Then I did the 2nd one last night and now am noticing the noise. Makes me pretty confident the U joint is good, and I got under there and checked it this morning.

 

I'm an idiot. I got under there again, cranked on the U bolts and tightened them down a bunch more. Felt like they were looser now that the rear was settling, especially after me driving it. Tightened them way down and just got back from a test drive, problem fixed. Happy 4th!