N80

I have a 2007 Enthusiast dedicated track car. 90k miles. Very few mods. Used Brembos added 3-4 years ago. New Z1 clutch last year. Square tire set up on Enkei wheels. Everything else is stock. Lately I have been getting a consistent high frequency low amplitude vibration between 100-120 mph in the straights under full throttle. So far only notice it in 4th gear but haven't tried 5th. Do not feel it in the steering wheel. No unusual noises.

Had tires re-balanced. No improvement. Rotating them did not help or change it. Lug nuts tight, etc. Wheel bearings all seem fine but are original. Steering and handling have not changed.

Any thoughts? Diff bushing? I do not get a clunk with shifting or acceleration/braking. Other bushings?

Thanks for any recommendations for where to start looking.

Sundown72

What corner is the vibration coming from? Is it the whole axle?
Were the tires checked for flat spots before they were re-balanced?

No amount of re-balancing will get rid of a flat spot, and those get worse with speed. Have the tire shop toss the assembly on the balancer and have a look across the surface as it spins, look for the dip.

Have you come in with hot brakes and kept your foot on them in the pit lane/paddock while waiting for traffic to clear?
How old are your rotors, and how much wear is left?

You can pretty easily warp a rotor by keeping your foot on the brake when they're hot. The rotor cools unevenly and you get hard(er) spots and the rotor can warp.
Worn rotors can more easily warp, and uneven wear may take the rotor out of balance (depending on how good the baseline balance was anyways).

Check the alignment, particularly toe and tie rods, and steering rack bushings. The rack can get pushed around and tie rods are consumables. You may have the two front wheels playing ping pong with the rack because a tie rod or rods is on its way out.

Lastly, your bushings are all almost 15 years old...which is to say they're outside the service window. I'm not sure they'd hold an alignment much through a track day, anyways...

Good luck.

N80

I cannot get any sense of the location of the vibration.

Tires are pretty new. Don't see any flat spots. Haven't locked up the brakes or anything like that.

Rotors are old but look fine and have plenty of wear left. No cracks. No vibration in the brake pedal. Cheap and easy to replace and since its time I'll likely do that anyway.

Will check all the front end stuff whenever I can get it up on jacks. No unusual tire wear after 3 track weekends so if alignment is out it isn't by much. And no vibration in the steering wheel.

Agree about bushings in general. Probably time to start replacing them as the opportunity or need arises.

Thanks for the tips.

Sundown72

No worries.

Good luck, I hope you can get it sorted. As for rotors, high carbon centric blanks for the win unless you’re dealing with serious pad knock back or trying to remove weight. Cheap, strong, reasonably vented, good initial balance.

If you’re really stuck, unhook the sway bar to see if that helps isolate the vibration.

You may want to check that the venting slot in the pads is clear, material can get caught in there and harden, causing wacky stuff with the brake pedal.

Let us know how it goes.

GreyZ

iTrader: (2)

I would check your rear wheel bearings. Mine had no vertical play, but hade a pretty bad pitch vibration. Could not confirm until I removed them and spun just the bearing by hand and could feel the roughness in the bearing even though there was no play.

travlee

iTrader: (8)

do you have black snot running down the subframe by the diff bushing?

N80

Not on quick inspection but need to get under car soon to look better. Might be able to do it this weekend.