mattbm2001

If this has already been posted I do apologize, I couldn't find any mention of it.

I bought my 99 z28 M6 March of last year. Like most used cars you get a lot of BS from the previous owner. It's been reliable and a LOT of fun. With that being said....

It's been going on since I bought it, but last night I took a friend for a ride in it. I got on the freeway near my home, and got on it on the on ramp. WOT through first second and third, but once I am around 100mph the the car starts rocking left and right, to the point you feel if you don't slow down, it will be all over.

I've also noticed the rear end in the car sounds like it bottoms out over a sudden bump, but is more prone to it with passengers in the car. Sounds to me like metal hitting metal, it's a very sharp impact.

As far as the loss of control feeling, the car has had tires replaced since I bought it with no difference, an alignment done by a reputable shop I've taken all my vehicles to and no change in behavior. Any help will be greatly appreciated.

777

iTrader: (21)

Check the swaybars first, sort of sounds like he might have removed the front swaybar to "save weight"

NewLS1Owner

iTrader: (6)

Mine does pretty much the same things. I'm pretty sure the previous owner of mine cut the springs to "lower" it. I'm about to replace all the shocks and springs. If i get it done in the next couple of weeks, i'll post up if it fixes the problem.

zracer323

iTrader: (12)

Definitely check to see if it has a front sway bar. The metal on metal sound could indicate the bump stops have been removed or could be the exhaust hitting the driveshaft.

BMR Tech2

iTrader: (5)

Sounds like a shock issue to me. At high speeds, shocks are moving very rapidly. This rapid movement is known as high-speed dampening which only has to do with the movement of the shock itself, not necessarily the vehicle's speed. Anyway, when a shock breaks down, its high-speed dampening is typically the first to go. The result is a car that "floats" around at high speed because the shock is not capable of "comprehending" the rapid changes in the road surface. The shock breaking down would also be why the car would bottom out over bumps.

It may also be a good idea to check out the sway bars as well since they can impact the response of the car at higher speeds, not just body roll.

Can you describe its behavior with a little more detail?

- Kevin