Vibrations...

Ok so I just bought this car three weeks ago... and I thought the highway vibration would be something simple that could be corrected easily... apparently not... I have replace all four tires, two rims, brakes all the way around, two REAR wheel bearings, two front NEW cv axles, two more axles to make sure they weren't bad, two new lower motor and trans mounts, flipped the upper mounts, balanced, rebalance, checked from end, rechecked front end, and aligned it twice. Then I removed the front wheels and brakes, raised it on the rack, put two stands under the front lower control arms, and spun it up to speed... the car shakes the whole rack... everything shakes, body, steering, brakes. I can see the engine and trans hopping around (nothing drastic), the cv axles.... everything. I am wondering if this is something in the transmission... I can't find any kind of documentation of a problem with the trans causing vibrations on the 97 newer trans, but I have one. I am thinking maybe a bad differential... output shaft bent... etc etc... anyone have any ideas? I have run out...

05 Grand Prix
3.8 N/A
4t65e (non hd)

Can feel a sort of wobble at lower speeds while lightly accellerating, or steady throttle coasting... when I let off, not apparent... as low as 45mph.

Vibration is constant from 61-75 (my average speeds... still there above 75)

Vibration shakes the steering wheel, body, seats, and engine.

Seems more pronounced under light accellaration on the freeway...

Scantool shows no weird data or misfires, dosn't feel like a running issue.
(if you want live data information let me know and I'll take a snapshot...)

Will still do it if I put the car in neutral, shut it off, and coast downhill at 70mph... Thats why with everything I have done, I am thinking something in the final drive of the transmission...)

ANY help would be GREATLY appreciated...

Thanks

Ray

How are the FRONT wheel bearings?

you got the struts, lca's and engine and trans mounts to check out still i guess. before diving into trans work.

is the motor moving around a lot? when you shift out of park see if it pops hard and moves a lot, or does it clunk real nice when you shift out of park? or forward to reverse, or vice versa. if so could be the mounts.

Ok...so I put in two more cv axles last night. Two new rims. It appears most of the body vibration is gone. There is still some there though. What I do still have is vibration while accelerating on the freeway that can be felt in the body and the steering. Not hard acceleration... Just slight acceleration. Also kind of feels like the vehicle is bogged down...I have replaced the lower engine and trans mount... And flipped the upper bushings. The lca's check out fine. It almost looks like the driver side cv axle at the engine is further back of center... And the passenger axle at the trans is toward of center... Like the engine is still sitting wrong... But all mounts have been addressed... Twisted subframe maybe.... ?

And the front Wheel bearings.... No play... No noise... .002 runout at the flange...

I know this is an old thread, but did you ever find the solution? I have the exact same description you have on a 2004 Monte Carlo. We have not changed my mounts yet but we see the motor twisted in the car like you describe also.