What could cause a 1998 mercury mountaineer to roar and vibrate when accerlerating it is an all wheel drive?

Answer 1

You may have a universal joint on one of the driveshafts going out. Do you hear any clunking or tinking sounds when you put the car in drive, and then reverse? If you hear any kind of a metal sound, then I would have the u-joints checked. Have you had your tires balanced lately? Did this happen all of a sudden? You may have lost a wheel weight. Do you feel and shake or shimmy in the wheel? If you feel shake in the wheel, look at the front wheels, if you feel the shake more in the seat of your pants then it is usually the rear. Have you had the vehicle in any deep mud lately? A clump of mud may have attached itself to the INSIDE of a wheel throwing the wheel weight off. Remove any clumps of mud and see if it helps. If you do not have the roar and vibration when the vehcile is only in 2 wheel drive then that leads me to believe it's in a driveshaft component to the axle that is not being used. Some vehicle use the 2 front wheels to drive it when it is in 2 wheel drive and some use the rear. So if you are using the rear wheels to drive the vehicle in 2 wheel drive the I would look closely at the front wheel drive unit. If your shaking and vibrating are only happening when you put it in all wheel drive, then it is NOT the tires nor the clump of mud. That will happen regardless if it is in 2 wheel or 4 wheel drive.