Axle bushing is the cushioning between joints in a car' s suspension system.

The bushes are designed to absorb the shocks of going over bumps and divots in the road, so they reduce over time. ... 

Made of a variety of materials from rubber to polyurethane and aluminum, bushings not only provide a smooth ride, they also deliver better handling characteristics and straight-line acceleration speed when used on a rear suspension.

When used on the front suspension, axle bushings are used on straight axle configurations and cushion the king pins to allow for a tight and controllable steer axle. When used on steer axles, many economy kits include plastic bushings that are often prone to premature wear and failure.

On vehicles with coil-spring rear suspensions, a four-point suspension package is common. Using two upper control arms along with two lower control arms, the rear axle is positioned in the chassis using axle bushings to cushion the ride characteristics.