General Procedure

Make a systematic check for unusual axle noise.
1. Select a level asphalt road to reduce tire noise and body drumming.
2. Inspect rear axle lubricant. The level should be within 9.5 mm (3/8 inch) of the fill plug hole. Drive the vehicle far enough to thoroughly warm up the rear axle lubricant.
3. Note the speed at which noise occurs. Stop the vehicle and put the transmission in neutral. Run the engine speed slowly up and down to determine if the noise is caused by exhaust, muffler noise, or other engine conditions.
4. Tire noise changes with different road surfaces while axle noises do not. Temporarily inflate all tires to 344 kPa (50 psi) for test purposes only. This will change noise caused by tires but will not affect noise caused by the rear axle.

Rear axle noise usually stops when coasting at speeds under 48 km/h (30 mph); however, tire noise continues with a lower tone. Rear axle noise usually changes when comparing pull and coast, but tire noise stays about the same.

Distinguish between tire noise and rear axle noise by noting if the noise changes with various speeds or sudden acceleration and deceleration. Exhaust and axle noise show variations under these conditions while tire noise remains constant and is more pronounced at speeds of 32 to 48 km/h (20 to 30 mph). Further check for tire noise by driving the vehicle over smooth pavements or dirt roads (not gravel) with the tires at normal pressure. If the noise is caused by tires, it will change noticeably with changes in road surface.

1. Loose or rough front wheel bearings will cause noise which may be confused with rear axle noise; however, front wheel bearing noise does not change whenever accelerating or coasting. Light application of the brake while holding vehicle speed steady will often cause wheel bearing noise to diminish. Front wheel bearings may be checked for noise by jacking up the wheels and spinning them or by shaking the wheels to determine if bearings are loose.
2. Rear suspension rubber bushings and spring insulators dampen out rear axle noise when correctly installed. Check to see that no metal to metal contact exists between the spring and the spring opening in the frame. Metal-to-metal contact at these points may result in road noise and normal axle noise which would not be objectionable if dampened by bushings.
3. Make sure that there is no metal-to-metal contact between the floor and the frame.

If the noise is coming from the axle, determine the type of axle noise before making any necessary repairs.