Vibrations at 50 miles per hour and up.

[6s2055]

I had a similar experience on my GT350. At around 80mph at both Sears & Thunderhill. Tried rebalancing as I thought the Houisers were losing too much rubber....sticky tires. Still same vibration. Had the drive shaft rebalanced and changed u joints, still there. Went to an aluminum drive shaft, still there. While adjusting the webers using a chassis Dyno, the shop owner experienced the same vibration. The final solution was that the angle of the rear end...the housing...needed to be reshimed as it a shade off. That was the solution for me. Just a possibility for your situation!

[deathsled]

I will take that into consideration.  Thank you for the tip.  My plan was to check out the tires today by overinflating them to 50 psi and trying to reproduce the vibration at speed..  I was totally lazy and didn't get out of bed till 3 in the afternoon.  Very uncharacteristic of me.  Then we got rain.  So I'll try tomorrow with the 50 pound tire inflation first.  But your idea is an important lead and thank you.

[shelbydoug]

One thing that I have found is that some individual tires are more sensitive to tire pressure.

Too much is bad. Tires will go "out of round" and/or won't stay flat across the tread.

It usually shows right out of the box on new tires when you try and spin balance them.

70mph vibration is usually the signature of an out of round tire/ Dealers here will tell you "it's illegal" to balance a tire for an  "illegal speed".

You need a race tire guy to work this out for you but I'd say you have a bad tire in the bunch?