My Z28 started just recently getting a vibration it first started going about 60mph and accelerating hard but not kicking the tranny down the car would shudder< let off the gas and it would stop hit again and it would come back I thought u-joints.
I had new high performance joints put in and had the drive line balanced while I was at it.

The vibration is almost none existant but now it gets a vibration that starts at about 80 and gets worse as you go up and gets louder when you let off the gas. Some help would be greatly appreciated I dont want to throw money were it is needed
THANKS

 

I got the same problem, it starts at about 65. I see you changed the u joints and it helped out a bit. I was thinking of doing the same. But mine feels like an air problem. Which I'm in the process of possibly fixing. I think my glass hood is poping up a little and allowing it to catch some air. I'm installing 2 more hood pins to see if that helps. Hopfully it will, it's been a while since I got it over 80 without it feeling like it's going to implode.

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92 RS, 350, Street & Performance MPFI, TFS heads,
Crane Rollers,
MSD Digital 6 Plus, 22lb injectors,
ZZ3 cam, Edelbrock Headers 1 5/8, 3" Exhaust,
Hi Flow 3" Cat, stock T-5,
stock rear 3.08, koni yellow adjustable front, twin turbo glass hood, T-tops, Auto Meter Ultra Lite Series 2 5/8 gauges, Teal Green

 

I now what you mean Ill have to watch the hood although it sound like its underneath.
thanks