Ok, had the U-joints replaced by my local shop (I could not break the caps loose on the rear). My "clunk" and 65-70 Mph vibration are now gone. But.....I still have a pop in the driveline. Slow speed rotaional poping sound, does not pop the entire rotation. Took it back to the shop thinking something was loose, bad u-joint, or whatever. They heard / felt the "pop" but were unable to reproduce it on the lift. When the truck is on the ground you can hear / feel it. When its on the lift (lifted by shock mounts) and you put it in drive there is no sound.

My Question(s);

Could this be a bad tranny mount? (suggested to me by the machanic) Upon close inspection all bolts feel tight and there are no visible cracks, even the exhaust mount attached to it looks good.

Or could this be a bad driveline angle only present when the driveline is "loaded"?

Is the driveline "loaded" (I mean have the weight of the truck on it when I say "loaded") when it is lifted by the shock mounts?

What else do ya'll think it could be?

Edit; Some more on the lift operation. The truck was put in drive and given gas to simulate acceleration. Drive shaft spun freely with no visible vibration or wobble.

 

how's the backlash in the rearend?

 

not sure. Rear end has never been messed with except a few months ago the fluid was changed.

more info. The sounds seems to come from the front. It almost sounds like a u-joint might be binding up and releasing (poping) at it rotates. I am starting to think it is a driveline angle issue. I just do not understand why when it was on the lift it did not make the noise.

 

On the lift there is no load. Apply the parking brake and then shift into drive. Then give it a quick shot to see if the drive line moves and pops. NOTE: this requires a functionning parking brake.

Regards

JMC