Q: Differential whining

The gears in a differential are helical gears. They normally don’t make noise unless they are worn irregularly. Low fluid levels are usually the cause of the irregular wear. This will cause the spacing between the gears or backlash to be too wide making them whine. Also gears that are not meshing properly can make a whining sound. In vehicles with high mileage this is normally due to worn bearings in the differential unit itself. Transmission slipping can be cause by several things. On an automatic transmission worn internal clutches or seals that are leaking internally can cause it to slip. On a manual transmission, a worn clutch will cause a slip condition. A qualified mechanic with the proper tools can determine what is damaged in both the differential and the transmission. Usually partial disassembly of the units is required for a correct and accurate diagnosis of your transmission’s whining noise.