Driveshaft Center Support Bearings

Driveshaft problems can be spotted from the moment you put the vehicle in gear to pull it into a bay. As the power is transmitted from the transmission to the rear axle, the slack from worn or damaged components is taken up, resulting in a sudden crunch or pop.

Once the vehicle is moving, you might hear a whine coming from the center of the vehicle. The noise will change as speed increases and might change as power is applied. If the vehicle is put into neutral, the sound remains the same.

The problem could be the center bearing's support. These are used if the driveline has a two-piece driveshaft. Engineers split the driveshaft into two sections to change the harmonics. The center bearing is a ball bearing mounted in a rubber cushion that attaches to a frame crossmember.

The cushion allows vertical motion at the driveline and helps isolate the vehicle from vibration. The bearing in most center supports is sealed for life. Some do have a zerk fitting from the factory, and some replacement units also have a way to lubricate the bearing.

Premature failure of the center bearing could be the result of too much driveshaft angle, the water shield being missing or damaged, road salt and moisture, or damaged rubber casings. Also, high mileage and bearing wear can contribute to premature wear. Other issues might be related to a leaking transmission or transfer case. Some of the additives in transmission fluid can rejuvenate seals in the transmission, but on the rubber of the center support bearing it can cause it to swell and degrade.

A small amount of noise is normal when using 4WD on a low-traction surface such as snow, ice, mud or sand. When operated in 4WD on a high-traction surface, such as clear pavement, the noise generated may be much more significant. This noise is the result of "driveline loading," which can naturally occur in 4WD.

As a vehicle travels down the road, the tires rotate a certain number of times per mile depending on the tire circumference. If all the tires are not exactly the same circumference, they will turn at different rates. On these trucks, 4WD is a "part-time" system designed for use only on low-traction surfaces.

This system has no internal differential, so the front and rear propeller shafts will turn at the same speed.

On low-traction surfaces, different tire sizes won't have much effect, as one tire can easily slip on the road surface to match the speed of the other tires.

On a high-traction surface, it is much more difficult for one tire to slip. Therefore, the 4WD operates under a "blind" to heavy-load condition, and noise is the result.

As tire rolling rates are a major factor in this condition, consider the following essential items:

Driveline noises caused by loading in 4WD vehicles may be mistaken for transfer case or front axle noise because they can sound very similar. 4WD noise caused by loading may exhibit the following conditions:

This noise should be considered normal and attempting to repair it will not result in satisfactory reductions to driveline noise. Any attempts to correct this condition by repairing these components may cause the customer to believe that the vehicle is unreliable and will also result in an inconvenience while their vehicle is out of service.