Possible causes of excessive transmission noise

GENERAL INFORMATION.

Noise from sources such as tires, wheel hub bearings, engine and exhaust system is often mistaken for transmission noise. The interior noise level can vary widely, since it depends on the

size of the vehicle as well as the type and quantity of sound-insulating

materials used. A transmission, like any gear mechanism, is not

completely silent. Therefore, a serviceable transmission always

produces a slight noise. To check the transmission noise level while

driving the vehicle, perform the following:

1) Select a section of road with a smooth asphalt surface to reduce the noise from tire rolling and the level of resonant noise in the cabin. 2) Drive the vehicle to bring all units to normal operating temperature.

3) Record the vehicle speed and the gear engaged at which

the noise increases.

4) Check for noise with the engine running at idle and the vehicle stationary.

5) Determine in which driving mode the increased noise occurs.

5a) Acceleration – smooth or sharp.

5b) Steady driving – vehicle moving at constant speed with a

small throttle opening on a level road.

5c) Engine braking – vehicle moving with a gear engaged and the

throttle partially or fully closed.

5d) In all of the modes listed above.

Bearing noise.

Final drive bearing noise can easily be confused with wheel bearing noise. Since the final drive bearings are preloaded, their noise should not noticeably decrease when the transmission is operating and the drive wheels are raised

off the ground.

Wheel bearing noise is characterized by its continuation when the vehicle

coasts in neutral. Since wheel bearings are not preloaded, their noise noticeably decreases when the wheels are raised and rotated.

Brinelling.

Brinelled bearings produce clicks or knocks at a frequency approximately

half the wheel rotation speed, since the rollers move more slowly.

Brinelling is the result of high forces pressing the rolling elements (balls or rollers) into the bearing race. Dents form on the

raceway. Brinelling occurs when a bearing ring is pressed onto a shaft journal or into a housing bore with the force applied through the

rolling elements and the other ring. Brinelling is also caused by vibration

acting on the housing part in which the bearing or rotating shaft is installed. An external sign of brinelling is small dents on the bearing raceway surface, making it look like a washboard. A defective bearing produces heavy low-pitched noise.

with rolling elements and the second ring. Brinelling is also caused by vibration

acting on the housing part in which the bearing or rotating shaft is installed. The external sign of brinelling is small dents on the bearing race surface, giving it a washboard appearance. A defective bearing produces a strong low-pitched noise.

Lapping.

Lapping is caused by fine abrasive particles such as scale, sand, corundum and similar materials carried by the oil. These particles wear

the raceways and rolling elements of the bearings. A defective bearing may have

significant play but run smoothly. Lapping is caused by

operating the vehicle with contaminated oil.

Seizure.

Bearing seizure occurs when large foreign particles get onto the raceway.

These particles can jam the rolling elements and cause one of the bearing rings to spin.

Excessive preload of tapered bearings can also cause them to seize.

bearings may also cause them to seize..

Pitting.

Pitting, or point spalling of the rolling surfaces, is the result of

normal fatigue wear under prolonged cyclic contact stresses.

Pitting may also result from incorrect bearing installation or develop after hard foreign particles get into the contact surfaces.

installation of the bearing or develop from hard foreign particles entering the contact surfaces..

Flaking.

Flaking, or scaly spalling and cracking of the rolling surfaces,

is the result of overloading or incorrect bearing installation (misalignment,

race tilt or excessive preload).