Differentials: Side Bearings
Side bearings are tapered bearings pressed onto the differential case that allow the case to spin inside the carrier. Manufacturers use shims or threaded adjusting nuts to place a preload on these bearings. Proper preload keeps the case from wobbling inside the carrier and adjusts backlash between the ring and pinion gear.
Side bearing preload adjustment is crucial to the differential's operation. If this adjustment is too loose, the differential case will move in the carrier, resulting in damage to internal components like the ring and pinion gear. If adjusted too tightly, they'll overheat and turn blue, similar to suffering a lack of lubrication. Faulty bearings make a growling sound that increases with rotational speed. This is true for differential side bearings. Misadjusted, worn, or faulty side bearings make a growling sound that increases with vehicle speed.