2 of my 3 cars ive ever owned have vibrated real bad at 70+. i had a 91 blazer and of course the firebird i have now. both do it. the blazer got better after i bought new tires. firebird had bad allignment due to a bent ti rod. i rode at least 4,000 miles on that bent rod, never rotated tires, is that the problem??

 

Vibrations can be caused by many things.Check the hiogh speed balancing, and your tire pressure as well. Also, if you hit any potholes really hard in the past you may have dented one or more of the rims which can cause a good amount of vibration. When I blew a tire i dented the rim, and drove with it with a new tire. Around 70 and up, i got vibrations. Sent the rim in for repair and when i got it back on, vibrations were gone. Thats all I can think of.

 

rims

 

I just went thru the same thing with my 89 rs I bought a last month.
I found and replaced a weak idler arm that helped some, I then replaced both front struts and the problem is gone.
It's a good bet the struts are the problem.
Try swapping the rear tires to the front and see if the problem is tire related, while you have the tires off check for worn suspension componets.

 

Anytime I had a problem with hi speed run a new set of rim made the difference. But is your from 70-140 or 70-80

a constant vibe can be a bad tire, rim or a warped rotor.

a vibe at say 50-55 only is probably a tire.

vibes at 7-80+ probably a rim tire balance combo.
50,000 miles stock steel rims will not be 100% straight.
Combo of new straight rim and then a tire balance form a rim change seam to be the sweet spot of the deal. Could just try to get them balanced. A good spin balance. But not sure what speed they balance them at. Need like a 140MPH balancer.

 

Its the driveshaft more then likely, I get this alot on the highway when im doing over 70. Here is a explanation...

"The stock steel driveshaft in the 1982-2000 Camaro and Firebird is 2-1/2" in diameter and has a critical speed of 7177 RPM. This is as fast as it should turn. While this may seem high, there is another factor to consider. At approximately half of critical speed - which is 4784 RPM - annoying vibrations can begin to occur."
-TPIS

You should just replace your driveshaft with the TPIS one. I am doing it it has a higher crtical speed, and is safe for speeds of 200+ mph so no more vibrations! Its aluminum so you save a few pounds and accel quicker

http://www.tpis.com
>Online Catalog
>Drivetrain
It is the first thing


$325 dollars

 

Used to have the same problem back when I still had the 195/65/15's on the front (yes, I do know they were too small... they were dry-rotting anyways so now they're gone). When I bought the new 215/75/15's to replace those last August, I also had a four-tire balance done. Problem solved...