Axle Nut
A large, high-torque nut that secures the drive axle shaft to the wheel hub assembly.
An axle nut (also known as a spindle nut) is a heavy-duty, high-torque fastener used to secure a vehicle's outer CV axle shaft into the wheel hub assembly. It is located at the center of the wheel hub and is exposed when the wheel and hubcap are removed. The axle nut applies a precise amount of clamping force (preload) to the wheel bearing assembly, keeping the bearing tightly bound and correctly aligned during vehicle operation.
Because of the massive loads and vibrations experienced by the drivetrain, axle nuts require extremely high torque specifications, often ranging from 150 to over 250 foot-pounds. To prevent the nut from backing off under operation, they are designed with locking features, such as a cotter pin slot, a crimpable collar, or a locking retainer key. Operating a vehicle with a loose or improperly torqued axle nut can cause rapid wheel bearing wear, alignment issues, and in extreme cases, the wheel hub separating from the axle.
Whenever a CV axle or wheel hub assembly is replaced, a brand-new axle nut should be used. Most manufacturers designate axle nuts as single-use fasteners because the locking mechanism degrades once removed. Mechanics must use a calibrated torque wrench to tighten the nut to factory specifications, as under-tightening causes bearing play and over-tightening crushes the bearing rollers.