About a month ago my 03 MCS started demonstrating this shimmy when I accellerate. It happens in the upper RPM range - most noticable when in 5th gear going about 70mph and I tromp on it. It happens when in other gears/RPM ranges but less so. Otherwise car is smooth and stable. I can be going 90 in 6th and car is smooth. When I floor it problem rears up. It's not even that acute - just never did that before. Car has about 63K mi. on it and good rubber. Haven't balanced tires in a while or had them rotated so I was thinking maybe this is related but the fact that it does it only under load bothers me. No noticable clutch slippage at all. I really don't drive it that hard ever so clutch shouldn't have any problems anyway. Any suggestioons?:impatient


BD

 

Since it's not happening during normal driving I wouldn't suspect tires/wheels. That would only be speed dependent, not load dependent.

If it only happens during times where you are putting load on the engine I would first suspect plugs, wires, or fuel pump/delivery. These have more demands on them during increased load.

Hope that gives you some ideas, I would probably pull the plugs and check the wires before I didn't anything to complicated. You might also have someone drive behind you and see if you blech any smoke during the times you have the problem.

 

The clutch/flywheel is a strong possibility. That symptom is exactly what my Explorer was doing prior to clutch replacement and now it doesn't.

 

My 05 MCS (8,000 miles) does something that sounds very similar. I would describe mine as a vibration (pretty subtle) that I can feel when I tromp on it from about 4000 RPM. Feels like I'm driving on rough pavement, except that I'm not. Dealership drove the car but couldn't feel the vibration. Otherwise, my car seems to pull strong.

I've never had a clutch go out in 30 years of driving exclusively stick vehicles, so I would tend not to suspect clutch problems here - it's certainly not slipping or chattering. Also I've just ironed out my tires/wheels, so they are rolling real smooth. I hadn't thought about the plugs and wires.

Not a real mechanic here, but was wondering about things like motor mounts. What does a mount issue feel like?

 

Clutch flywheel,changed under warranty.Problem gone.

 

I know in Hondas, this is a classic sign of cv joint failure. If the clutch/fw proves to be not the cause, you might consider the cv joints.

 

Just to complete the story for those of you interested enough to reply - I took the car in and had the tires rotated and balanced. Problem gone....

BD