When i get to around 50 or 60 it feels like a drive train vibration but if i accelerate it smooths out. My first thought is u-joints....agree or disagree?

 

I've had tires out of balance that would only vibrate at certain speeds.

 

but this doesnt fel like a tire it fels like its up the midle undewr my ***

 

Depending on which tire and just how out of round it is the sensation of the vibration can move around. Take all four wheels off and check their balance first. On my daily driver I have a front left tire that feels out of balance until it reaches operating temperature. The fact that it goes away at other speeds means it probably is a tire doing it to you. Anything else would be constant and get worse as you accelerate. If it was a front tire that was badly out of balance the steering wheel would shake and you would be aware of it.

I have 103,000 miles on my 1988 and it has never made any vibration other than from the wheels that I could feel. Your rear wheels are not far from "under my ***") as you so aptly described. The rear wheels are more likely to be out of balance and cause the sensation under your butt. Drive shafts U-Joints make a lot of noise while they are failing naturally.
I have exploded a out half shaft u-joint but with a 550+ hp C3 it is easy to do if you are abusive to the car. I replaced the drive shaft U-joints while the engine was out of the car, it was a lot easier to do it then.

There is an important saying that I have trouble with at times. If it ain't broke, don't fix it! Too often when looking for a problem we make five or six new ones while we are at it. These Corvettes were well engineered and are good reliable transportation normally. My 1988 Corvette is virtually stock with only ignition modifications on the car. It gets 30 mpg on the highway even with the Rear end "Performance Ratio" of 3.07 and the anemic L98 while cruising along at 60 with the A/C on listening to the stereo. Take some time and learn to enjoy your Corvette! We are here to help those with questions so keep us posted on what you found, how you fixed it and so on.

I wish you the very best in getting your Corvette running properly!
Chris

 

thank you for your insight...you are correct
I enjoy that car even when I have to fix something

 

A quick way to check things.....Get the car up to speed and put it in neutral.... if you still feel the vibration its tires, wheel or wheel bearing related...... If its gone then look toward the drive line related components...

 

Great point. I've done this many times over the years and it led to tire issues every time. Now, one of the first things I do to every car I get is purchase the lifetime alignment and balance at my local shop. Well worth the money to have an alignment check and balance on a regular basis,

 

good call....thank you

 

Thank you for your response, I will have those areas checked out

 

I have a 2014 C7 with the 6 Sped Automatic Transmission. The car has 10,500 miles on it. Recently I noticed a cyclical vibration over 55 MPH. I took the car to the local Corvette Center who only work on Corvettes and they rebalanced all 4 tires, the 2 fronts and 1 rear were out of balance by 1/2 to 1 ounce.
The corvette center said that should solve the problem.
It didn't, on the way home on the highway the cyclical vibration was still there, so I called the Corvette Center back and told them.
They said that the next thing to do would be to replace the front tires as they were showing some wear in the inside edges, rebalance and align the car.
The rear tires they said looked ok. All 4 Michelin Run Flat tires were made in 2013 according to the side wall markings.
If replacing the front tires still doesn't eliminate the vibration, then they would look at the drive train. The vibration is not in the steering wheel.
Any ideas? Should I go ahead and replace all 4 tires with new Michelins to totally rule out that it's a tire issue?

 

If they were made in 2013, change all 4, vibration or not. Then see what happens.

 

Ok, thanks for the suggestion. I'll let you know how the new tires work out in a few weeks when I get them installed.