I am trying to figure out the cause of a vibration before I bring the truck into the mechanic. This vibration starts at about 50km/h - 30mph and is only felt when i have my foot on the gas. When i let go of the gas the vibration stops (when i coast). The vibrations nearly stop until the speed of 80km/h. There is a low hum that starts at about 100km/h. I had the wheels balanced while it was in for an oil change last week but that did not help the vibration at all. And the vibrations do not seem to be related to rpm. It is only 2 wheel drive 1999 with about 235 000 km automatic. Searching over the internet has come up with about 5 differnt answers with the most common being u joints. Any help would be appricated. Jason

 

check center shaft bearing?

 

I'm thinking drivetrain too, u-joints may be a good place to start if you have not already. Also have you checked your wheel bearings? Can you feel the vibration in the steering wheel or just through the "seat of the pants"? Being you say that it vibrates worse under power maybe rearend or tranny problem? Maybe a bad tranny mount?

Vibrations can be very hard to pin down, especially when you rely on someone elses descriptions of the symptoms. Hope everything works out OK, and cheaply too!