vibration at high speeds

[Sic96]

I seemed to have developed a vibration at high speeds. The car is smooth up to about 85/90; after that, I can feel a noticeable vibration. It gets worse the faster she goes. It seems to be coming through the clutch pedal more than anything. If I press the clutch in, the vibration stops and it's smooth as glass, the second I let the pedal back out, the vibration is back. What does this sound like?

Things worth mentioning:
Stock rear-end
Aftermarket LCA's with no relo bracket
Lowered about 2" via Eibach sportline PRO springs, KYB AGX shocks/struts all the way around
stock panhard
Stock driveshaft
stock clutch I'm assuming

[DanDalessandro]

Curious. How do you not have an adjustable Panhard bar. They are usually a requirement for lowered cars. I don't know if that would cause issues.

But I would get LCA relocation brackets and an adjustable Panhard bar. Your pinion(?) angle changes when you are lowered, as well as the centering of the rear. The geometry so to speak... Could be something dealing with that.. Founders has great products that are absurdly affordable

[Sic96]

Right, I listed the PH bar for that reason. I was thinking that had something to do with it. They should be changed out when lowered for sure, but I don't think it's a requirement. I need to do it though, it's causing stress on other parts I'm sure. I'll check founders out. Thanks

[zeeman]

It wont cause stress. but things wont be centered. The torque arm keeps the pig pointed at the transmission. I hate to say it but I think its a Clutch issue.
Pressure plate or disc is out of balance would be my guess.

Also, check your universal jounts, less likely but possible. The reason I say that is. It is possible that load on the joint is forcing it out of alignment causing it to come out of balance. Normally you would notice it before this as a clanking upon clutch engagement.

Try this. When you feel the vibrations note the rpm range. Then when parked. Rev the motor to that rpm. In nuetral, clutch out, then with the clutch in. See if the vibratin shows up. If not look @ the rest of the drive train.

[Sic96]

You know after reading this last night, I started remembering back a while ago about some clutch issues I was having. They went away for a bit and I focused my attention on other things. But yeah, I think you may have nailed it. I was just thinking in a whole other area of the car. I scheduled a day with a tranny guy I know, and he's gonna check it out hopefully this weekend.
It's starting to not like engaging in 4th gear, and every time I start it cold, the tranny makes this rattling chatter until it warms up or while cruising at a low rpm, like 1800. Sounds like s***, almost like a nasty exhaust leak. I'm still going to install a panhard and some lca relocation brackets, already ordered them from Founders, and yes they are very affordable. I'm almost certain this is what it is now. thanks for the advice. It needed a clutch years ago anyway.

[DanDalessandro]

The reason I mentioned the panhard bar was because I was having terrible vibrations and stability issues at high speeds when I got new tires (went from big 315s in back to 275s all around). I replaced the Panhard bar because it was my one of my cheap options.
It looked like this when it came off. No more vibrations and the car is much more stable.


Hope you get everything solved man.