My truck started doin' this slight bounce that took me a while to figure out was drivetrain related. At first I'd feel it and thought did I just imagine that, eventually feeling it for certain got out and made sure all lugs were tight. I then went to the drive line. Pulled it off and replaced the u joints that were replaced late last year. Still have that bounce.

But here is what I notice, light throttle, cruising speed and when the road starts to decline while holding constant speed is where I feel it. I've been able to control it by cruising on the FW at 60mph and keeping the throttle in use to keep the gears in mesh. So if the road starts to decline I'll let off the gas slightly to be able to speed up down it to about 60mph.

This past weekend I pulled off my drive line again and noticed about 1/4" to 1/2" (aprox) slop when rotating the 3rd member flange back and forth. Curious if any of you have that much play/slop?

Anyway anyone else have this type of issue? I swore it was a U-joint but they are new with no slop.

 

My rear driveshaft will turn almost a half inch before "biting." Nothing wrong with that.

I'm curious as to what you mean by "bouncy." Is it bouncing when you come to a stop? Lots of body lean/roll in the corners? Shuddering during braking, or driving?

Finally, do you have manual hubs up front? Checked tranny/diff fluid levels?

More info plz.

 

It has to do with the drive shaft or 3rd member. under power its perfect, but letting off the gas, maintaining a constant speed and then going down hill is where the truck will literally start bouncing, a shimmy, shutter. What ever you want to call it. No not under braking, not warped. Manual hubs of course.

Fluids were checked this past weekend. I can't tell what is up, I know there is a bit of vibration but its not constant. If I'm on the freeway getting off the off ramp and just toss it into neutral as I coast down the ramp I have a good bit of vibration and then around 40mph its gone. But it all has to do with no power and or in that middle of power and coast.

 

Hmm... I'm not familiar with 3rd members, sorry. The only thing I can think of is a worn center bearing. I dunno if your truck has one though. I know my buddies 91 Ex cab long bed had a bad shudder when coasting at speed until we swapped his center bearing out. It could be moved about a half inch in every direction...

Good luck, hopefully some gear head can chime in!

 

You may want to check and see if the nut holding that drive flange is tight enough. I'd check the tcase end as well.

 

Play causes vibration. Locate the excessive play and there's your problem.