Just rebuilt the Tranny (sm-420) and installed. On test drive under accelaration no noise, when I let off the gas and coast, I get a vibration and banging sound what I think is coming from the drive train. Feels like the u joint, also the problem existed prior to pulling the tranny.

How can I be sure it is the U joint? and if it is, do the rebuild kits work okay?

Thanks all.

1951 Chevy 3100 5 window with a 1958-60 235 and original 4 speed.