Shock absorbers, or struts, are one of the most important suspension components in any car. Their only function is to absorb the shock impulses caused by road bumps and stop the car from jumping up and down. With time, they wear out or even fail completely. As this affects driving characteristics and poses a safety issue, it is important to replace them if there are any symptoms.
- Mechanic toolset
- Torx socket set
- Jack and jack stands or lift
- Plastic pry tool
- Magnetic tool
- ½” breaker bar
- ½” 17mm deep socket
- W251 Shock absorbers (always change in pair)
Step 1 - Prepare the vehicle
- Park your car on level ground where there is enough room to work around it.
- Open the trunk lid and remove light bulb access panels on both sides.
- The quarter panel trim is held in place by several plastic tabs and one screw. Start by looking for a Torx screw located at the bottom corner of the quarter panel and remove it using an appropriate Torx bit.
- Remove the quarter panel trim by pulling it out of its place. The retaining plastic tabs should snap out. If needed, use an appropriate plastic removal pry tool.
- Repeat this procedure for removing the quarter panel trim on another side.
Step 2 - Unbolt upper bolts.
- The upper side of the shock absorber is held in place with two self-locking nuts. Locate them at the side of the trunk floor and remove both using a ratchet and 14mm socket. When removing the nut and washer that is beneath it, take extra care not to drop it. You may need a magnet for this.
- Repeat this step on another side of the vehicle.
Step 3 - Raise the vehicle in the air.
- While the vehicle is still on the ground, break free all lug nuts on both rear wheels, but don’t remove them yet. You may need a breaker bar and a 17mm socket for this.
- Locate lifting points underneath the vehicle and raise the rear end in the air.
- Find a suitable position and place a jack stands so that the vehicle is rested securely on them.
- Remove all lug nuts and then take the wheel off. You may need to wiggle it around or gently hit it with a rubber mallet.
Step 4 - Remove the shock absorber.
- On vehicles with Airmatic and ADS (Adaptive Damping System), there is an additional cylinder on the side of the shock absorber with one wire coming out of it. Locate the connector at the end of the wire and unplug it.
- The bottom side of the shock absorber is held in place by a bolt and nut assembly. Using a pair of 14mm sockets or wrenches, undo the nut and remove the bolt.
- Maneuver the shock absorber out of the way and put the new one in its place.
- Reinstall the bolt and nut that holds the bottom side in place.
- Repeat this procedure on another side
Step 5 - Lower the vehicle
- Carefully lower the vehicle while ensuring that the upper strut brackets are sliding back into their position.
- Once the upper strut brackets are in place, reinstall washers and bolts.
- Reinstall remaining parts and trim pieces in reverse order.