s7ven

This is a problem that I have done a lot of research on but it seems like the resolution is different in just about every case. There seems to be a lot of potential causes ranging from unbalanced/bent wheels, bad brake components, unbalanced/bent/worn drive train components, and even bad or misaligned suspension components.

So, I'll explain my issue the best that I can, hopefully get some advice and get it fixed. Then hopefully this thread will help someone in the future.

Pertinent Car Info:

• 2001 Pontiac Firebird TA M6
• Completely stock drive-train
• Lowered on Strano springs
• Koni shocks on all 4 corners
• Strano front and rear sway bars
• Adjustable Founder's Panhard(Poly/Rod ends) with relocation
• Kooks headers and Kooks true duals
• Poly engine mounts
• BMR DSL
• New balanced wheels/tires on rear with less than 1000 miles on them

Symptoms:

• Passenger seat and shifter both shake violently *sometimes*
• Feels like the source of shaking/vibration is the rear
• Has gotten progressively worse since owning the car (2.5 years) and seems slightly better after recent new tires/wheels on the rear
• During a trip, regardless of speed or road conditions the shaking will transition from violent to no shaking and back again
• Shaking is amplified at higher speeds
• Shaking is still there even if I put the car in neutral

So that is pretty much the current scenario, any help is greatly appreciated. I think what I really need help with is what tests and diagnostic methods should be used to rule out certain components. I will probably be replacing the whole drive train behind the transmission and all stock rear suspension components later this year but until then I thought this would be worth troubleshooting.

hrcslam

In neutral while still moving?

Is your steering wheel shaking too?

Have you checked all your bushings and ball joints already?

Do the symptoms change with tire rotation?

Is your torque arm bent?

s7ven

Yes in neutral while moving. Steering wheel has very little to no shake.

My front wheels have no play in them when I try to move them at 12 and 6 with the car jacked up so I am thinking the ball joints are good but if there is another test I should do let me know.

I have not checked any bushings yet but I will soon.

Certainly possible on the bent TA, I used to have bad wheel hop. Is there a better way to tell other than visual inspection?

The vibration severity does seem to coincide with wheel rotation speed.