Originally Posted by
JohnnyE
My 6-speed, 2005 roadster limited’s problem is tough to diagnose. It just started at 135k miles. When I accelerate straight ahead, using heavy throttle and no matter what gear I’m in, when the engine climbs into its peak torque range, the rear end of the car does one quick left-right wiggle. Just about an inch or so, and it IS noticeable. It’s just a single wiggle, and it lasts less a few tenths of a second. When I drop of the throttle, I get that same, quick, left-right wiggle. The wiggle is snappy and it's scary on wet roads. Hitting a sharp bump in the road at highway speed causes the same wiggle. It must have something to do with the torque from the drive shaft.
During all of this the steering wheel is rock solid…the problem doesn’t seem to be in the front steering or suspension. If you leave your hands off the steering wheel, the rear does its wiggle, but the steering wheel doesn’t budge, and the car still tracks straight ahead. If I drive along a shallow left-hand curve at the correct radius and speed (60 or so mph) the wiggle becomes a continuous oscillation that does not stop until I change my speed, alter the radius of the curve, or do something to break up a harmonic vibration. It does not happen in a right-hand curve. Only to the left.
The cause does not appear to be the wheel bearings, shocks, alignment, wheels or tires. These have all been changed or verified within spec, and the problem is still there.
The rear suspension components check out, including the bushings. One race shop I trust says the problem is in the four rubber bushings that mount the rear subframe to the unibody. Okay, I’d like to know more, but that isn’t even in the CD –ROM service manual. The bushings look ok...they're not torn or anything obviously wrong. The bolts are all tight. The shop could wiggle the subframe in relation to the unibody, but that’s what rubber bushings are for...to allow movement. How much movement it too much?
Has anyone had this problem and have any ideas about the cause and how to repair it?