I just bought a 1999 4runner V6 4x4 with 210k miles. It has a high frequency vibration coming from what seems like the driveshaft. I took the driveshaft off and had it rebuilt by a reputable driveline company in Denver. While it was off I had to use the truck so I drove it in 4WD using only the front shaft. The vibration was completely gone at any speed, smooth as glass. Put the rebuilt rear shaft on and vibration is immediately back. Long story short, the driveshaft has been back to the shop 4 times now, gone through "race car" style balancing and rebuild again only to have same problem each time once reinstalled. So the driveline shop decided to build me a new rear driveshaft from scratch, and now the vibration is actually worse and the new driveshaft has lasted 300 miles before the ujoints are making a lot of noise. (The old rebuilt driveshaft has lasted far longer (1000 miles) with no noise, just vibration) I am at a loss. The vibration is such a high frequency, it seems like it could only be coming from the driveshaft, and when it's off the truck is perfect. I don't think the shop is incompetent but there is something definitely wrong here. Anybody have any ideas? I have been pouring through forum threads, googling until my eyes look googled themselves. I don't want to spend a ton of money on a brand new driveshaft if it could possibly be something else causing the problem. Please help!

Pertinent information -
No lift
Brand new Aftermarket wheels 16"
Brand new Hankook 265/70/16 tires
Alignment done 3 months ago
Vibration starts @ 55mph and continues through 80mph, certain speeds are worse than others but the vibration is consistent. Accel/decel doesn't seem to affect much but there is a noticable difference sometimes.
One of the driveshaft rebuilds was better than the others, less vibration, almost undetectable. Should have stuck with that one I guess because now it is far worse.

 

have you been greasing your u-joints? if not your ujoints may be gone.

 

Does it have a CV joint that was rebuilt? I had a similar problem. The normal CV u-joints are easy to replace. The oddball center one is only available aftermarket and the tolerances suck.

I lost one of the needle bearings from my OEM joint and had to buy the aftermarket replacement. No one has been able to balance it since I did this. It is now my trail spare.

 

Have you checked your rear pinion bearing or T-case bearing? Flanges move at all?

 

by any chance has it been in an accident? If so frame might be damaged thus causing it to vibrate, One of our work trucks hit a curve and actually shiffted the diff and ended up twisting the drive shaft 2 times, we had to scrap it. YIKES! hope this isn't your problem
Other possibility is that it may be your tranny clutches sliping 'If it's auto' or a bad clutch 'if auto'