Ring and Pinion Gear Noise
There are two types of gear noise. One type is produced by broken, bent, overheated or forcibly damaged gear teeth. This noise is usually quite audible through all speed ranges and can easily be diagnosed upon visual inspection. For example, hypoid gear tooth scoring generally results from the following:
- Insufficient lubricant
- Improper or contaminated lubricant
- Insufficient gear backlash
- Improper pinion depth
- Improper ring and pinion gear alignment
- Improper pinion bearing preload
The scoring will progressively lead to complete erosion of the gear teeth and, eventually, a fracture will result if the initial scoring condition is not corrected. Another common cause of hypoid gear tooth fracturing is extended overloading or shock loading-causing the differential pinion gears and shaft to seize. This can result from lubrication breakdown caused by excessive wheel spin. The second type of gear noise pertains to the contact pattern of the ring and pinion gear teeth. This form of abnormal gear noise can be recognized because it produces a cycling pitch (whine). This whine will be very pronounced at the speed range in which it occurs. Because the front differential is driven (powered) in four-wheel drive only, this noise can only be duplicated in four-wheel drive. Gear noises in the front differential can occur under one or all of the following conditions:
- Drive-is under acceleration or heavy pull. The pinion gear riding on the drive side of the ring gear.
- Float-is only enough throttle to keep the engine from pulling the vehicle (between Drive and Coast). The vehicle slows down gradually with the engine pulling only slightly.
- Coast-is with the throttle closed and the vehicle in gear. The pinion gear riding on the coast side of the ring gear.
Gear noises tend to peak at a narrow speed range or ranges and tend to remain constant in pitch. Bearing noises will vary in pitch with vehicle speeds. For further diagnosis, refer to the appropriate noise diagnosis table.