Pinpoint Test A: Rotational Or Knocking Noise From Axle

All gearsets and roller bearings, including those found in the axle, generate some noise during normal operation. Some normal noises may be perceived as severe when the vehicle is raised on a hoist and the listener is closer to the axle.

A worn ring and pinion gearset can produce a whine or whistle type of noise. The noise comes in at certain vehicle speed. The noise will peak and fade away usually within a 5-10 MPH (8-16 km/h) range. The noise may be present in one or more drive conditions: tip in / tip out / coast / cruise.

Worn pinion bearings can produce a scraping noise. This noise will be a continuous low pitched noise starting at low speeds.

Worn differential bearings can produce a growling or grinding noise that increases with speed and load.

Gear tooth damage on the drive side of the ring or pinion can cause a knock noise. This noise can occur at various speeds and is not affected by acceleration or deceleration.

Excessive backlash can cause a driveline clunk that occurs as the vehicle starts to move forward following a stop. Excessive backlash can also cause a chuckle or knock type of noise that will be heard during coast and deceleration. Excessive backlash is caused by ring and pinion gear wear.

Gear tooth damage on the coast side of the ring or pinion can cause a chuckle or knock type of noise that will be heard during coast and deceleration.

As the bearings or gears wear, metallic particles are shed and distributed into the axle fluid. This metallic contamination can cause the other components in the axle to fail. The ring and pinion gears, pinion bearings (included in -4209- kit), differential bearings (-4221-), and differential bearing cups (-4222-) should be replaced when repairing an axle for the noise concerns described in this diagnostic test.

Possible Sources 

• Normal gearset noise
• Differential bearing worn or damaged
• Pinion bearing worn or damaged
• Ring or pinion gear tooth damage

• Compare the noise to a similar vehicle. Use an NVH analyzer or a decibel meter app to quantify the noise volume/intensity. When selecting a comparable vehicle, attempt to match:
  • axle design (8.8 in, 9.75 in, with or without ELD, etc
  • vehicle build configuration (XL, Lariat, SuperCrew, Regular Cab)
  • tire brand, size, and condition
  • vehicle mileage and condition
  • NVH analyzer sensor or decibel meter location
  • vehicle location / environment (wall or building proximity, weather or environmental conditions)

Is the noise in the subject vehicle similar to the noise from the comparable vehicle?