Mevotech Control Arm Bushings isolate and reduce transmitted noise, road shock, and vibration. When a vehicle is in motion, axial and radial movement of the suspension system, combined with the excess heat generated by the vehicle, cause the bushings to twist and stretch. These stresses can lead to hardening, cracking, and even breaking. This normal wear can be increased by rough road conditions, or by worn or defective shock absorbers, further shortening the life of the bushings. Worn bushings can allow surrounding components to change positions often causing excessive noise in passenger cabin. Once bushings have begun to harden and crack, they must be replaced. Sold as kit per side.