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[Wild Fire]

Hey guys,

I have an 06 G6 GTP with the LZ9 3900 and the F40 six speed manual.

I figure I'll come here because there seems to be a lot of knowledge in a very small place.

I have lowered my car on Eibach pro-kit springs (1.5 drop) and now have vibration issues under load. This is a VERY common occurrence with lowered 6 speed sixes and only the 6 speeds. The autos have none of the same problems.

All that I can think of is that when you lower the car, you essentially lengthen the driveshafts in relation to the hubs and that the auto has more give for this type of thing. Obvious solution is shorter shafts, but how to figure out how much shorter ?

Also, because it only happens under load, I am wondering if my stock engine/tranny mounts are letting the engine/trans torque too much and changing the geometry enough to make that little bit of difference ?

Any ideas ?

[95SleeperAcheiva]

I run eibachs myself. Make sure your alignment has been corrected for the lowering. Usually you'll get a camber change. Also keep in mind a stiffer spring rate will give you more "feel"

Axle legnth won't effect it the way your thinking or you would feel the vibration everytime the suspension gets loaded under normal springs.

[Wild Fire]

Alignment is corrected, and when the springs compressed under stock springs, the same thing happens. Just doesn't take as much when lowered.

[gpse3400]

Its not so much the length as it is the angle. The axles need to be relativley level with the vehicle stationary with only a slight angle upward from the transmission out to the knuckle, nothing you couldn't possibly tell through visual. Another problem you have by lowering the car is the wear pattern of the CV joints as a whole has changed. The only way to correct it is to revert to stock suspension springs, raise the engine up some, or new axles-(that is depending your angle is not so much off).

Axle shafts themselves do not lengthen but the the tripod joint allows lateral movement of the axle relative to the location of the knuckle at a point in time. Shortening the axle itself will only cause it to ride on the outer edges of the joint, which would cause even more problems.