hey guys, I know this post has been up a million times, but I couldn't find a good answer with search. Here is the deal, as soon as I hit around 50+ I can feel a bit of a vibration, or shuddering. Probably more of shuddering, as I consider vibration to be more rapid, with a more high pitched noise, and something that you feel absorbed by your body. I have what I would call a shudder, meaning its not quite as rapid, the sound and feeling seem *deeper*, and rather than my body absorbing it, I feel it kind of shaking my body. Now this shuddering is kinda bad around 80mph, but seems worse in different speed ranges, not necessarily faster. I also dont notice it increasing with RPM's so much as opposed to speed. Once again its worse in say 65-73 than 73-80, and then worsens again above 80. But it varies a lot, and maybe its just my imagination. I had a similar problem checked out a while ago and my mechanic said nothing was wrong and that one tire was minutely out of balance and that he fixed it. Yeah, good story. So now I'm in college 4 hours from home, and I drive back alot. On long highway stretches it drives me nuts, and takes away from the stability and secuirity that I should be experiencing at 90 in a ls1 z28. So needless to say im kinda pissed, and even more frustrated. Here is a list of possibilities I think it could be.

1. Wheels/tires are out of balance, and the mechanic didn't really do much or balance it well.
2. Alignment is off (the car runs pretty straight though at high speed even when i let go of the steering wheel, veers a little to the left though)
3. Driveshaft problem (Same mechanic who told me all was gravy replaced my rear drive shaft seal and I remembered this while trouble shooting and I think this problem started getting worse after he replaced the seal)
4. Transmission Mount (70k miles and never been replaced, also when I engage the clutch most of the time, not from a complete stop, i can feel the car wobble kind of, and I've seen some movement in my stick, which from what I've read is definately attributed to my trans mount)
5. Lastly, I hit a pothole this winter which is why I took it to the mechanic in the first place, cuz i thought one of my axles/rims might have gotten bent)

SIgh....so many factors and im , and at the same time that this is happening. All advice is GREATLY appreciated, and if you are anywhere in Virginia, or withing a few hours of Virgnia Tech, if you could recommend a shop that would be awesome. Thanks guys.

 

Information on a vehicle would help.... Z28???? Ls1???? Any mods to the suspension??? My first guess would be the drive shaft out of balance at those speeds...

 

sorry bout the lack of info......i forgot i don't have my sig showing yet <<<(noob move), anyways its a 1998 Z28, with magnaflow catback, and a airlid. Thats it. Thanks again.

 

btw how much should it cost to have my driveshaft balanced?

 

i have the same shudder/vibration and it got worse when i changed the worn/torn stock tranny mount to a Poly mount.. i have a 1999 LS1 z28.. i dont think its the tires cause the shudder comes every 1-3seconds depending on the speed.. could it be that the weights from the driveshaft came off and it needs to be rebalanced??