The early Mercedes AIRMATIC struts have a polarizing reputation. The comfort they bring when they are functioning is balanced by the prohibitively expensive repair costs when they go wrong. On chassis that aren't worth nearly what they were ten years ago, the cost of replacement may not be worth it for some owners. However, if you are willing to use aftermarket parts and complete the labor yourself, the cost will come in near a more expensive coil spring suspension replacement.
Arnott, the company that makes the replacement air-springs, has updated Mercedes' original spring design to be more reliable and cheaper to use. These springs remove the need for the OE air reservoir, simplifying the installation process and significantly reducing the length of time it takes to install them. Other than a special socket required to remove the air-line fitting, this job only required standard sockets and wrenches.
Mercedes models and years applicable:
Symptoms of a failed rear Mercedes AIRMATIC strut:
- "Stop, car too low" error message on the instrument cluster
- Sagging rear suspension
The front AIRMATIC strut is a typical modern air-strut. It uses a damper, similar to that of a coil-spring suspension, and has an airbag placed over and around the strut in place of the spring. However, on the rear suspension, the air-spring sits inward of the strut, on the lower control arm's strut.
The rubber bladder that makes up the spring is prone to leaks and is often the cause of the failure. If the bladder isn't the issue, the problem will lie with one of the air-supply hoses' fittings. If you drive the vehicle without a functioning air-spring for too long, you will damage the shock absorber.
How much will it cost to replace a Mercedes AIRMATIC strut?
Fixing the rear air-suspension isn't cheap. However, the redesigned parts are better than the original OEM units and will last longer. The real money saver here comes from the use of aftermarket parts and doing the labor yourself.
The kit we used to fix the rear suspension on our W211 will cost you roughly $750. This kit comes with both rear air-springs and the required parts. You can buy one rear air-spring on its own, but we highly recommend replacing both springs at the same time.
Also required for the job is a special socket used to remove the air-line from the spring. The socket will cost an additional $37.
How long will it take to replace a Mercedes AIRMATIC strut?
Replacing the rear air-springs shouldn't take you too much time. Budget around three hours to complete this job. That should take care of any hang-ups from rusty bolts and nuts.
Parts required to replace a Mercedes AIRMATIC strut:
Tools required to replace a Mercedes AIRMATIC strut:
- 10mm Hex Bit Socket
- 13mm Socket
- 16mm Socket
- 16mm Wrench
- 17mm Socket
- 18mm Wrench
- 21mm Socket
- 21mm Wrench
- Electric Ratchet
- Torque Wrench
- Air line Socket
- Diagonal Cutters
Steps required to replace a Mercedes AIRMATIC strut:
Step 1: Access the rear air spring
Jack the rear of the Mercedes into the air and remove the wheels. Use a 17mm socket to remove the wheel bolts.
After that, locate the bolt for the toe control arm. Use a 10mm hex bit socket on the bolt's head and an 18mm wrench to counter-hold the nut.
Be careful when you remove the bolt; the tension in the bushing will force the arm upward. Next, disconnect the swaybar endlink from the knuckle. Use a 16mm socket to remove the bolt and a 16mm socket to counter-hold the nut.
Then, use that same 16mm socket and wrench combo to remove the strut's lower bolt.
Next, take a 21mm socket a wrench and remove the lower bolt for the air-spring.
Depending on your situation, you may need to remove the remaining air from the spring. To do so, follow the instructions provided at this link.
Now you'll need to disconnect the air-line from the spring. To disconnect the line, use the special air-line socket linked above. First, place the socket over the air-line nut.
Then use a 13mm wrench to rotate the socket and break the nut loose. There is very little torque on the nut, so you won't have to rotate the socket too far. Once it's broken loose, use the socket and your finger to back it off all the way and disconnect the line.
Now that the line is off, you need to remove the nut from the air-line. A plastic collar prevents the nut from coming off the air-line and line it up in the spring. Use the split in the collar to break it, and then slide the nut off the line.
Next, grab the diagonal cutters and cut the zip-tie on the strut to free the air-line and wiring. Follow that wiring to the plug on the top of the air-spring and disconnect it from the spring. If you have any trouble pressing down the tab on the spring's electrical connector, use a flathead screwdriver.
Step 2: Replace the air-spring
Use a pry bar between the chassis and spring to pop the spring out of its upper mount. Then, use a knife to cut the thick air hose connected to the spring.
Then, push the toe control arm down and out of the way with one hand while you pull the air-spring out with the other.
Now, get the new air-spring onto a work surface and remove the seal from the air-line port. Then, thread in the new air-line fitting supplied in the kit. Thread it on by hand before using the socket and 13mm wrench to tighten the fitting gently.
That completes the prep needed on the spring. Head back over to the chassis and remove the spring's body mount. More often than not, you can unscrew the mounts by hand. Use a pair of pliers to rotate the mount and remove it if it doesn't come out by hand.
Install the new air-spring after you thread on the new body mount. The metal alignment plate above the lower shock mount will only allow you to install the spring one way on the control arm.
Next, take the air line and press it into the fitting. The new fitting will grab the end of the line and keep it locked into place. Give the line a small tug to ensure that it is seated fully. After that, plug the wiring harness into the air-spring.
Step 3: Bolt everything back together
Start by installing the bolt for the air-spring. Use a jack to raise the control arm slightly to line up all of the bolt holes. Then, slide the bolt through and thread the nut on by hand to avoid cross-threading. Before torquing the air-spring bolt, install the lower strut bolt and thread on its nut.
Then, install the bolt and nut for the swaybar endlink and for the toe control arm. Use a 10mm hex bit socket to drive in the toe control arm bolt and use an 18mm socket to counter-hold the nut.
Now, take the jack, place it under the control arm, and raise the suspension to ride height. This is necessary to torque the bolts as it allows the bushings to be compressed at ride height.
For the air-spring bolt, se a 21mm socket to torque the nut to 150Nm and use a 21mm wrench to hold the bolt's head.
Use a 16mm socket to torque the strut nut to 50Nm, plus 90° of rotation, and use a 16mm wrench to counter-hold the bolt's head. Then, torque the swaybar endlink bolt to 70Nm. Use the same socket and wrench from the strut bolt on the endlink bolt.
Lastly, use the 10mm hex bit socket and 18mm wrench to torque the toe control arm bolt to 50Nm, plus 90°.
After that, remove the jack from the suspension and refit the wheel. Remove the wheel hangar from your tool kit and thread it into one of the holes for the wheel bolts. Then hang the wheel on it and install the bolts. Use a 17mm socket to thread in the bolts and torque them to 85Nm.
Step 4: Cycle air through the suspension
Now that you've installed the new air-spring, it needs to be filled with air. Head into the cabin and start the vehicle. Then, press the button used to raise the suspension.
Air should now fill the rear springs. Exit the car and examine the level of the rear suspension. You'll know you've done everything right when there aren't any error messages, and the suspension is sitting at the correct height.
Mercedes AIRMATIC strut torque specs:
- Mercedes Air-spring Bolt = 150Nm or 110.6 ft-lbs of torque
- Mercedes Strut Bolt = 50Nm or 37 ft-lbs of torque, plus 90°
- Mercedes Swaybar Endlink Bolt = 70Nm or 52 ft-lbs of torque
- Mercedes Toe Control Arm Bolt = 50Nm or 37 ft-lbs of torque, plus 90°
- Mercedes Wheel Bolt = 85Nm or 63 ft-lbs of torque