Whining from the rear of a RWD Ford Transit - differential or wheel bearings?

A whine that increases from the rear axle of a rear-wheel-drive Transit can have several sources, and it is worth identifying the correct one before repair because the axle contains six bearings. A useful workshop diagnostic clue is whether the noise changes with throttle. A whine that becomes louder under acceleration or on overrun points to the pinion bearings. A constant rumble that does not change with load is more likely to come from the differential carrier bearings or wheel hub bearings; worn hub bearings also change tone when the van is steered gently from side to side.

How can you prevent rear axle failure on a Transit?

The most common underlying cause of worn axle bearings is old oil or a low differential oil level, an item often neglected for years during routine servicing. It is worth changing the axle oil every 40,000-60,000 km and checking halfshaft end float whenever the brake pads or shoes are replaced. A whine caught early usually means replacing bearings and oil seals. If ignored, it can end with replacement of the crown wheel and pinion or the entire axle. Rebuilding a differential requires correct gear mesh and bearing preload, so it is a job for a specialist.