i have a vibration that i thougt was a u-joint but replaced it. it happens when you give the truck just enough gas to keep it going. if you take your foot off the gas or accelerate it will go away. there is no play in the t case yoke or the diff yoke. checked wheel bearings and they seem good. anything i missed?

 

When you checked for play, did you put the tranny in neutral and chock the wheels(leave the parking brake off too). This will take any load off the drivetrain.

 

yep i sure did. i was thinking it was one of the brake drum weights that i knocked off, but the vibration is too fast. i keep thinking it is a bearing but they seem ok

 

I just noticed you have an older truck like mine. My rear driveshaft is like the front, it has a slip yoke in the middle of the driveshaft. If this joint has any sideways movement at all, it can cause the vibration you described. When there's torque on the shaft, the splines are held tight, and it won't vibrate. When there is no torque, the splined joint can flop around. You can try putting a little grease in the joint and see if it goes away for a little bit. Also, I can't remember if it's keyed or not, but when you put it together, make sure the front yoke on the shaft, is in the same plane as the rear yoke which is welded to the shaft. The u-joints won't work together, and can cause a vibration if the yokes are not lined up.

 

Motor/tranny mount maybe?

Frank

 

slip yoke. your are right i do have one. i didnt think of that. i will take a look at it today and shoot some grease in it. i guess that there should be no play in it, other than sliding in and out, right? thanks again.

 

"there should be no play in it, other than sliding in and out, right? "

Right. And take another look at the alignment thing too.

 

i will take a look at it tonight. thanks again.

 

checked the slip yoke in the rear and it seems good, i do need to replace the one in the front driveshaft. i double checked that when the t case is in 2 high that it wasn't still spinning the front and its not. this vibration thing has be beat. anymore ideas?

 

I had a similar problem... tried everything you did and what I found was a really bad lower ball joint... replaced both upper and lower ball joint and bingo... vibration gone.