Where to start with vibration

I have a vibration while in motion and in the gas. What I have done so far,

Checked and adjusted the timing and carb - not here.
Adjusted clutch - it's new, - not here
Looked for obvious play in driveline - no obvious slack

If I'm cruising at 45(or anywhere from 15-60) in the gas and put in neutral to coast, the vibration completely goes away. So I'm thinking the u-joints? The phase looks correct on rear.

 

Any slop in the U joints or slip yokes?
Check the wheel bearings too.

 

Does it get worse the faster you go? Driveshaft may be out of balance.

 

Worn driveshaft U-joints are a very common problem, and will cause a vibration. When I've had that, it vibrated in coast and not under power, but I suppose it could just as easily be reversed.

 

X2 i lost the needles in one cap after i made a hard launch, boy did it vibrate.

 

I had a similar vibration in my 81 Cherokee Chief, Turned out to be Pinion Bearings were shot in the Model 20 AMC, I thought it was U-Joints because one of them was a little loose, When I had the rear drive shaft out I grabbed the yoke and found out I could wobble it around almost a quarter of an inch. The seal oddly enough was only seeping a little but not really leaking.

 

I know it sounds dumb but check your wheel ballance

 

Did this just start? If so...I'm with the bad u-joint guys. If it's always done it...could be driveshaft angle. Could be that your rear-end is tilting upward just enough when on the throttle to give it a weird angle.

 

No, just started after putting in a new clutch. Thought the phase of the rear driveline was out. Looks dead on. Slight play in rear u joint to yoke. Wheel weights are still on tires. U joints are cheap so I guess I'll start there.

I also would think it would vibrate on coast and under power as the driveline is still spinning. But who knows.

Additionally 2nd gear seems noisy. Sounds like it's in 4wd when in 2nd gear. A lot of gear noise. Fluid is fresh and topped off. 1st and 3rd are tight but second has a little play and can come out of gear without the clutch and has been know to pop out if I jam the gas or come out of the gas fast. Is a rebuild in order?

 

You have a T-15 right?
Yeah...it sounds like it could use some freshening up.

 

Another thing you might check is the motor mounts. Is one of them broken?

 

Another thing to check. I did the trans mounts and torque stud when I did the clutch. The engine mounts are the original rubber with no life left.

 

I had the same thing happening to me..the rear u joint had just a tiny bit of play but that was enough to cause vibration. changed both u joints last weekend and she rides smooth now.

 

You say it all started after a clutch change. Check to see all that the transmission, transfer case and bell housing bolts are tight. Did the transmission always jump out of 2nd gear or did it only happen after the clutch job?

 

Second has always been a little sloppy. Still not that bad. I'll go through the bolts again - good point.