vibration under acceleration

[cmryhldr]

I am trying to figure out a problem with my son's '99 4runner v-6 2 wheel drive truck. (around 140,000 mi.)
Starting somewhere around 30 mph it starts vibrating under acceleration. If you remove your foot from the gas the vib. goes away. Press pedal and it starts again. We jacked up the back end today and I got under the truck. (we used jack stands) With the parking brake on and foot on the brakes, with truck running at idle, go from reverse to drive and it sounds like one tap with a hammer on a hollow tube. From drive back to reverse the same noise. This noise is more noticeable at the front of the drive shaft.
Also, the front U-joint is very rusty but I could not see any motion from it during this gear changing.

Any ideas or info on what is causing this?

Not going to get too involved with it until after Christmas.

Most everything I could find in search pionts to U-joints.

Thanks for any suggestions.

cmryhldr

[kball]

Sounds like U joints to me. I'd try lubing them first and see if that helps. If it's bad enough to cause vibs though it may be too late for that to help.

[jetwhine]

cmryhldr,

Ditto...................

[cmryhldr]

Well, I finally got around to changing the U-joints. One spider bearing was completely shot on the front joint. The needles were non existent, just full of rust. Truck is vibration free now.
cmryhldr

[jetwhine]

cmryhldr,

Alright another happy camper. Hope you have many carefree miles ahead of you.