Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Typically a vibration that only occurs when you accelerate is due to a bent or failing axle shaft.
Are you getting any kind of noise from the front end- especially when cornering?
Well, I would probably take a look at the CV axles and make sure there aren't any signs of a failing axle shaft (grease on the boots, torn boots, or shiny metal that has been rubbing or binding). You could also make sure the axle joints aren't loose by prying against them with a pry bar to see if they move around a lot.
It's safe to assume the tires have been balanced? Check for signs on the rims that a wheel balance weight might have fallen off.
Right, a wheel balance issue shouldn't go away when you let off, but sometimes the vibration isn't as prevalent because the vehicle inadvertently drops speed. Some driver's perception of a vibration isn't as precise as other's.
A vibration from a bad axle shaft shouldn't be as noticeable when the vehicle is off the ground, especially if it was lifted from the frame. When the vehicle is lifted off of the front suspension it will pull down on the axle shaft, often enough to hold it steady and dampen the vibration. If you lifted the vehicle from the control arms, thereby keeping the suspension loaded and the axle shaft in the normal driving position then you would likely still feel the vibration if it is in fact an axle shaft issue.
Let me know how it goes.
Were you able to feel any play in the axle shaft's u joints?
If you aren't getting any vibrations with the car lifted off of the wheels then the only explanation should be a problem with the wheels or tires. I know that doesn't make sense since it only happens on acceleration. I suppose it's still possible that the problem is in the axles and you don't feel it when the car is lifted because there is no rotational load on the axle shafts, but that is going to be hard to determine. When the wheels were spinning in the air could you see any wobble or variation in the wheels or tires?
I'm still suspicious of the axle shafts. It sounds like you have thoroughly checked the wheels and tires. The only thing left to vibrate would be those axles.