Help! Weird shake/vibration/clunking at high speeds

[99Mounty]

I have around 53k in my 1999 AWD Mountaineer.

For some odd reason, when I drive at speeds around 35-45 mph, my vehicle "shakes"... it doesn't seem like a vibration ... it kinda jerks, as if it's having a hard time changing gears ... at the same time, i feel it on my seat. I'm not sure if this is an alignment issue or not -- at first, I thought it was a tranny issue. I changed the tranny oil, put new filter -- but that didn't help. After that, I drained the transfer case fluid and filled new oil in the tranfer case -- that didn't help.

Could this be as simple as an out-of-balance tire? Or do you think this is more serious -- as in a damaged tranny, damaged driveline componets?

I took it in to a shop, and the guy said it could possibly be my U-joint.

Any help/insights/ideas/suggestions are greatly appreciated. Please help!!!

 

[Raschied]

U-joint

Questions:

Is the "shake" more noticable going straight, or around corners?

Is the vehicle noticably pulling from one side to the other?

are there any noises associated with the "shake"? i.e. a clunk when accelerating? braking?

Does your Tach jump or shift at the point the "shake" occurs?

lastly, does it do it when you take your foot off the accelerator?

 

[99Mounty]

the "shake" and the "vibrating" is noticeable going straight, the vehicle does not pull from one side to the other.

along with the "shake" is sort of like a grinding noise ... it sort of "clunks" lightly when accelerating, ... even when my foot is off the gas pedal. my tach does not jump at the point when the "shake" occurs.

I took my vehicle in today to get an alignment and to get tires balanced... turns out my tires were not balanced. however, even after getting tires balanced and getting an alignment, i still get the "shake."


any help please??

 

[Raschied]

U-joint

If you don't mind climbing under the car, it's pretty easy to check the U-joints and the drive shaft for obvious problems. That's where I would start. Clunk when accellerating is a good sign the u-joint is giving way.

I'm not familiar enough with the X's drive train to give you specifics, but you should try grabbing the drive shaft on either side of the u-joint, and try giving it an "indian burn." That is, check to see if there is any play in the joint if you turn on half of the shaft clockwise and the other counter-clockwise. If you feel any movement, the joint is bad.

I had this happen on a little 124 Spider sports car, and had the same symptoms - vibration in a speed range, clunk when accelerating. One look under the car showed the problem. U-joint was so bad it had almost sheared off.

If that's not it, start suspecting the differentials. Usually it's more noticable in the corners if the differentials are to blame.