Diagnosing vehicle noises
Faulty front or rear wheel bearings, heavy tread tyres, exhaust resonation noises, and vibrations are often confused with gearbox or differential noises. Experimentation without solving the problem could cost you money.
The correct way of diagnosing differential noises is to road test the vehicle. Jacking up the rear and running the vehicle in gear will not simulate on road conditions and loadings, and I advise against this practice. The uneven turning of the rear wheels will result in fast spinning of the planetary gears, causing loud noises, and masking the real fault.
Heavy shuddering or banging noises on cornering indicate worn or scored crownwheel and pinions. Humming noises which do not change from acceleration to deceleration indicate worn pinion bearings. Scraping or rumbling noises which do not change from acceleration to deceleration indicate worn carrier or wheel bearings. Constant knocking noises generally on deceleration indicate chipped crownwheel or pinion teeth. Excessive backlash is normally a planetary gear problem.
Gearbox noises are always more pronounced in lower gears. Constant rumbling noises indicate worn bearings. Knocking noises in a particular gear indicate chipped teeth. Difficulty in engaging gears indicate worn synchros, gears or selectors. Noises which occur in neutral with clutch depressed indicate worn thrust bearing.
Vibrations are rarely caused by differentials or gearboxes, and in most cases are caused by out of balance tailshafts, worn centre bearings, worn universal joints, worn gearbox yoke or extension housing sleeve, or out of balance wheels.