Rear Axle Shaft
A solid steel shaft that transfers rotational power from the differential to the rear wheels in rear-wheel drive vehicles.
A rear axle shaft is a heavy, solid steel shaft used in rear-wheel-drive (RWD) and four-wheel-drive (4WD) vehicles with solid rear axles. The shaft is splined on its inner end to lock into the differential's side gears and features a flange on its outer end where the brake drum or rotor and wheel are bolted. Its job is to transfer rotational torque from the differential to drive the rear wheels.
Rear axle shafts are categorized into semi-floating and full-floating designs. In semi-floating axles (common in light trucks and SUVs), the shaft supports the weight of the vehicle in addition to transferring torque. In full-floating axles (common in heavy-duty trucks), the wheel hub rides on bearings on the outside of the axle housing tube, meaning the axle shaft only transfers rotational torque, allowing it to be removed without raising the vehicle.
Over time, rear axle shafts can bend due to heavy loads, off-road driving, or curb impacts, causing wheel wobble, tire wear, and vibrations. The outer axle bearing and seal also wear out; a failing axle seal will allow gear oil to leak out onto the rear brake assemblies, ruining the brake pads or shoes. Mechanics inspect axle shafts for runout using dial indicators.