Vibration when going over 90MPH

[06GTAuto]

I've noticed over the last couple of days that there's some weird vibration on my car when I'm going over 90MPH. I recently had the Steeda Underdrive Pulleys and Lower Control Arms (the billet ones) installed on my car, so I'm thinking that if must have been something that was done wrong when those two things were installed (they were installed the same day). It's not a vibration that causes any noise, just seems like something is out of line. I took the car to a friend that has a tire shop asked him to align the tires because of the problem I was having, he told me not to do it, that aligning the tires was only going to involve them working with the weights on the rims and he didn't want to charge me for that and not solve the problem. What else should I be checking? The car is fine until you go over 80-90MPH.
Thanks!

 

[bigcat]

is there any problens at that same rpm in a lower gear? if it is only above 90, then i would say its probably in the wheel balance. if it is at a certain RPM, then it could be the U/D pullies.

 

[White05GT]

I've noticed over the last couple of days that there's some weird vibration on my car when I'm going over 90MPH. I recently had the Steeda Underdrive Pulleys and Lower Control Arms (the billet ones) installed on my car, so I'm thinking that if must have been something that was done wrong when those two things were installed (they were installed the same day). It's not a vibration that causes any noise, just seems like something is out of line. I took the car to a friend that has a tire shop asked him to align the tires because of the problem I was having, he told me not to do it, that aligning the tires was only going to involve them working with the weights on the rims and he didn't want to charge me for that and not solve the problem. What else should I be checking? The car is fine until you go over 80-90MPH.
Thanks!

I had this problem after using one of those fix-a-flat cans -- it was an emergency.

 

[Spdfreak]

Check the fluid in your flux-capacitor.

 

[06GTAuto]

is there any problens at that same rpm in a lower gear? if it is only above 90, then i would say its probably in the wheel balance. if it is at a certain RPM, then it could be the U/D pullies.

It's only when I go above 80-90MPH, like I said before, the car is fine if I just rev it while it's stopped, or during a normal drive where I stay below 70MPH, no vibration at all. I thought it might have something to do with the tires, when I got home yesterday I jacked the car up on both sides and switched the two rear tires, thinking that maybe they got switched when the LCAs were put in. Took the car for a test drive after switching the tires but the vibration was still there. I would switch the front tires but I don't think they were removed!