Suspension struts, sometimes known as McPherson struts (named after their inventor), are a combination coil spring and shock absorber. The upper part of the strut is mounted to the vehicle's body or frame, and the lower part of the strut is secured to the lower suspension control arm. The full weight of the vehicle rests on the strut's coil spring, while the compressed gas within the strut smooths out bounciness and roughness in the ride much like a shock absorber would. When the strut is no longer performing as it should, the entire strut needs to be replaced.
Set your vehicle's parking brake. Work on either the front or rear of the vehicle at a time. Raise the vehicle with a hydraulic jack and place two jack stands under the frame so that the suspension and wheels are hanging down freely. Do not place the jack stands under any suspension components.
Remove the wheel lug nuts on the raised end of the vehicle by turning them out in a counterclockwise direction with a lug wrench. Lift the wheels off of the hubs and lower them to the ground. Set the wheels aside.
Locate the bolts on the upper side of the strut by checking inside the boot compartment for rear struts and under the hood for front struts. Remove the bolts in a counterclockwise direction with an adjustable wrench and set them aside.
Locate the lower strut mounting bolt on the lower suspension control arm from underneath the vehicle at either the front or rear, depending on which end you are working on. Remove the bolts with an adjustable wrench in a counterclockwise direction and set them aside.
Remove the loosened struts from the vehicle and discard them.
Place the new struts into position from underneath the vehicle by lining up the upper mounting studs of the strut through the holes in the mounting area on the vehicles frame or body. Replace the lower mounting bolt through the strut and into the lower control arm and tighten it with an adjustable wrench in a clockwise direction.
Replace the upper strut bolts from either the boot compartment or under the hood, and tighten them in a clockwise direction with an adjustable wrench. Replace the wheels and tighten the lug nuts in a clockwise direction with a lug wrench. Remove the jack stands and lower the hydraulic jack slowly to the ground. Re-tighten the lug nuts with the lug wrench.
Your struts may need replaced if your vehicle is sitting noticeably lower than usual or sagging. Your struts may also be defective if you notice abnormal tire wear or if the vehicle bounces when going over bumps. Before removing the front strut on some vehicles, you may have to remove the flexible brake line clip and push the brake line out of the way.
Always replace struts in pairs in the front or rear. Never replace only one strut on your vehicle or its handling can be adversely affected. If you are working on a front wheel drive car, support the lower suspension control arm after removing the front struts by placing a block of wood under the wheel hub. This will keep the front suspension from hanging down too far and damaging the constant velocity (CV) joints.