My 88 Firebird has a VIBRATION above 50MPH. The vibration seems to be comming from the the Transmission Tunnel aft of the shift lever. Its an automatic 700R4 with a 2.8L V6. Below 50, everything is fine. But as soon as I get on the highway and go above 50, the VIBRATION comes on Like gang busters.
Is it possible the U-joints are BAD? They have never been replaced. I am the Original Owner of the car. Could the Transmission Mount be the problem?
Any advice would be appreciated.

 

I'd start with checking balance on the rear tires - with the torque arm coming up to the rear of the tranny, you could have a bad balance and it's sending vibrations up the torque arm. Make sure to get a spin balance, and regardless of what the balancer guy says, make him balance them to 70mph, they can do it, they just are usually too lazy to.

 

I have already had both front & rear wheels high speed balanced and all is well. The only other thing I havn't checked is engine mounts.
I'm going to replace the u-joints seeing as they have NEVER been replaced. If that doesn't work, I'll look at the engine mounts.
Thanks for the advice on the wheel balance. That was the first thing I did when this vibration started.
I'm just woundering if the front alignment could cause this Vibration??

 

And you've examined both the trans and torque arm mount?

JamesC

 

In addition to the great suggestions already posted, be sure to check that you don't have an engine misfire. You could have either a wire or plug or other electrical fall out at a certain erpm. Try putting your car in nuetral, set the park brake and run your engine VERY slowly up to about 2000 erpm. You could also check your ujoints and trans mount as they'll play a role.

 

The Transmission mount appears OK. However, the Torque arm mount has NEVER been Replaced. I think I'll disambnle the torque are and replace anything that doesn't look right. The engine mounts have NEVER been replace either and maybe the front alignment may be off.
Thanks for the suggestions.

 

either driveshaft imbalance, or transmission internal related, try 50 in 3rd gear then 50 in 4h and lockup, that way you know if its tranny related. check your local driveshaft shop to see if they can check the balance on the drive shaft

?
does it go from no vibration to crazy vibe, like 50 nothing at all to 51 vibration?

reason being is that only certain thing causes certain vibration symptoms