What Causes a Rear End Whine?by Chris Weis
Noises that originate in a differential can travel up driveshafts and across axles, confusing diagnostic efforts. The sound level can bring minor annoyance, or foretell serious part failure. Timely reaction to a rear end whine may prevent the need for repair or replacement of expensive differential components. Understanding differential parts and maintenance may help determine the severity of the problem.
Eliminate the Basics
Any gearbox will be noisy if the fluid level or quality is deficient. Differential fluid can become contaminated by water entering the housing through air vents or axle seals. This commonly happens when venturing off-road or driving on flooded streets. A replacement lubricant may require friction modifiers or an exact viscosity specified for your model of vehicle. No substitutions should be attempted. Rotate your tires to diagnose their involvement. Whine at a different location after rotation may indicate a defective tire.
Get Your Bearings
Many differential components are mounted on bearings. Worn or dry bearings are capable of a wide range of noises that may change frequency with vehicle speeds. An axle bearing can create whine in the rear end, but will be more prominent on one side of the vehicle. A whine that occurs only on deceleration is often related to the pinion gear bearing. The pinion gear is turned by engine force and subject to bearing wear from the forces applied.
Quiet gear action is directly related to proper matching of gear surfaces. Maladjusted or worn gears create whine at different speeds or loads. The whine will be constantly present, but may change pitch or intensity. Early detection may reveal a simple repair or maintenance requirement. Untreated rear end whine will worsen over time and may be the only warning of imminent differential failure. Substantial wear or damage is usually attributable to abuse or extreme mileage.
Bearing pre-load and gear mesh are carefully measured and meticulously adjusted by trained and experienced technicians during assembly of a differential. Dyes are used to ensure mating surfaces are correct and backlash is set to strict specifications to deter or eliminate whine. Special equipment like dial indicators and inch-pound torque wrenches are calibrated regularly to maintain accuracy. While differential design may seem simple enough, the precision required for quiet, dependable function is best left in experienced hands.
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