Bawls

I'll start with the mods I've done on the suspension/chassis:

Eibach Pro-kit lowering springs
BMR Tubular Subframe Connectors
Moog Outer Tire Rod Ends
Moog Control Arm Bushings
Moog Lower Ball Joints
Lakewood Boxed Rear Control Arms
Lakewood adjustable panhard rod
Energy Suspension Poly Transmission Mount
Energy Suspension Poly Sway bar End-Links
Weld-in Relocation Brackets (using bottom setting)

I also have a set of 18" AR Rebels with Kuhmo 275/35-18's.


Now here's what I'm experiencing. I've got an idea of what these problems might be coming from, but I would like some other opinons.

Around 50-70MPH I get a vibration coming from the rear:
Pinion angle because I lowered it with the pro-kit? I don't have an angle finder, so I havent figured this one out yet. Also could be driveshaft being out of balance. It's the stock steel shaft with almost 140k miles on it. Maybe Ujoints?

I've noticed since the new wheels/tires (I did the rear LCA's and panhard at the same time) I get a lot of oversteer while cornering. Are the Kuhmo's just that bad? Or is this a product of low profile tires having less sidewall to compensate?

I've got a set of strano's revalve's coming in when I get off deployment in august. Gotta Love Iraq.

Bawls

help

Dave '97 Z28 M6

Lowering the car would affect the pinion angle, and that might be the source of your problem. Was the driveshaft removed, and if so, was it re-installed the same way that it was before? You wouldn't think that it would be fine one day, then bad the next. Can you pinpoint when the vibration started?

That's likely due to the Lower Control Arm relocation brackets more than anything. Maybe a higher setting will correct the suspension geometry for the lowering - the lowest setting might be too much. If the LCAs are close to parallel when the car is sitting normally, that's the best for handling. When the rear of the LCAs are lower than the front, that maximizes straight line traction, but introduces oversteer.

You've added a lot of stuff to your car that uses poly bushings. While poly bushings are street friendly, they are a lot stiffer than the factory rubber bushings, so they will cause more noise/vibration.

OBE1 95Z28

Since you rebuilt your front suspension I'm assuming you had an alignment performed. The alignment settings could be contributing to your steering issues.

An adjustable torque arm requires you to set the pinion angle; without an angle finder, you can't properly set the pinion angle. Sears sells one for around $10.

Greed4Speed

Which Kumho's?

Bawls

Honestly, Ive been dealing with the vibration for about 8-9 months, so I really cant recall when it started. The problem is I lowered the car the same time I put a rear in with 3.42s. So when I pulled the driveshaft I could have possibly rotated it. I dont see why I would have pulled it though, it's not like it gets in the way. But I'm sure I did.



Ah okay, I was always under the impression you wanted them on the lowest setting all the time for any situation. Since I like the twisties more then straight line, I'll check that out.

I knew the poly would add more noise and vibration, but i didn't know too much about binding. What exactly is it? Think this could be a contributing factor as well?

Bawls

Could be, I had the body shop align it after they did some minor body work to it. (no frame damage or anything)

They didnt get it right the first time and I had to go back. I'm definatly going to get an alignment when I get back to the states.

Bawls

712's. I've heard horror stories of them.

speed fiend

Your poly rear control arms could be the cause of your oversteer issues. The poly bushings restricts your rearends ability to articulate, causing increased roll stiffness(bind). For cornering, you would probably want arms with rod ends to eliminate binding.

Bud M

That's the first thing I'd change to reduce oversteer

Greed4Speed

I have 712's and they do suck in a bad way. I'd imagine they're not helping the situation, but not the main culprit. Should have bought better tires is handling is a concern.