The shock absorbers, also referred to as struts, on a BMW are extremely important aspects of the suspension, if not the most important aspects of it. Over time, shocks wear out, leaving your BMW with a soft, bouncy ride. If shocks are left to deteriorate for an extended period of time before being replaced, the safety of the vehicle can be compromised. Replacing BMW shocks or struts is a relatively intensive job, particularly for the layperson, but can be done with the right tools and approach. Keep in mind, that though this article describes the replacement of a single shock, these should be replaced in pairs or all four at a time.
Park the vehicle in a well-lit area that is also flat and level. Loosen the lug nuts for the wheel that has the shock you will be replacing. Lift the car using a floor jack and lower it onto jack stands. Finish removing the wheel and set it out of the way.
Spray degreaser where the lower part of the strut is bolted to the suspension and wipe it down with a rag. Disconnect any lines that are fastened to brackets on the strut housing. Depending on the model, this can include the brake line and the brake wear sensor line. Remove the wheel speed sensor for ABS-equipped cars. This is held on with a small bolt. The sensor slides out of the back of the hub.
Remove the large bolts holding the brake caliper to the strut housing. Slide the caliper off the rotor. Support the caliper while you work. Remove the bolts where the steering arm attaches to the strut. These are generally accessed from below. Disconnect the sway bar from where it bolts to the strut housing.
Open the bonnet. Remove the three nuts that fasten the upper strut to the chassis strut tower. Slide the bottom of the strut assembly away from the suspension and down from where the studs on the top of the assembly go through the sheet metal.
Move the strut assembly to a work bench. Place a spring compressor on the spring, ensuring that the hooks for the spring compressor are directly across from each other. Carefully compress the spring until the tension against the top of the strut housing is relieved.
Remove the rubber cap over the nut that secures the strut bearing. Carefully loosen and remove the nut, ensuring that the tension on the spring is completely relieved. Remove the nut, washer and any spacers. Slide the upper strut bearing and the spring off the strut housing.
Transfer any pads or spacers at the top and bottom of the old strut to the new strut. Leaving the spring compressed with the compressor still fastened, slide the spring over the new strut. Slide the upper strut bearing onto the strut. Install and tighten the nut that holds the upper strut beating on. Carefully loosen the spring compressor, ensuring that the spring seats correctly in the top and bottom of the strut assembly.
Reinstall the top of the strut first by sliding the studs at the top of the assembly up and through the holes in the sheet metal in the car's upper strut tower. Loosely install the nuts to hold it in place. Slide the bottom of the assembly into place. You may need to press down on the suspension and steering components to get the bolt holes to line up. Reinstall the lower bolts. Tighten the upper and lower bolts.
Reinstall the sway bar, the brake line and other lines on their respective brackets and reinstall the ABS speed sensor, if applicable. Reinstall the brake caliper. Replace the wheel and hand-tighten the lug nuts. Lower the car to the ground and finish tightening the lugs nuts.
The procedure is similar for the rear shocks, but is often easier, since on most models the lower shock is simply bolted to the trailing arm with one large bolt. Also, there will be minor differences throughout the installation depending on the year and model of the BMW.