V12 Uber Alles, Changing the Rear Struts in a W140 Mercedes Benz

Changing the Rear Struts

The rear "shocks" in a S600 are not really shock absorbers at all. They are hydraulic struts. They are very similar in principle to the hydraulic rams you see on the front of construction equipment. These struts have a supply line feeding them with hydraulic oil pressurized by a portion of the power steering pump. To get a complete understanding of the system, read my ADS page.

I was hearing a bumping/rattling/creaking from the right rear. The sound was coming from an area up near the top of the rear seat. It was especially noticeable during slower speeds. It sounded like an old creaky wooden ship. I first thought it was the bump stop on the top of the strut, but it turned out to be the strut itself. I was able to isolate the noise by grabbing the strut, and having a person push down on that corner of the car. The creaking was clearly felt inside the strut.

These ADS / Self Leveling struts are pretty expensive, so don't be surprised when you see the prices.

Tool needed:

1/4" ratchet drive
1/2" ratchet drive
10 mm socket
19 mm socket
10 mm box wrench
17 mm line wrench
19 mm line wrench
Brass punch
Hammer
Car ramps
Good Penetrating Oil (not WD40)

Parts Needed:

Hydraulic Suspension Fluid, P/N 000989910310 (comes in 1 liter bottles)
Strut MB P/N 1403209913
Possibly steel pressure lines connecting components, if corrosion requires cutting lines to disassemble.

Time Required:

Anywhere from 2 to 8 hours. Less time for cars without corrosion, more time for cars with corrosion.

Please use caution during this project. The rear suspension oil is under lots of pressure. The oil could spray out under high force. It is important to follow the instructions carefully. You should be wearing safety glasses at all times. If you don't usually wear them, make an exception for this project! This is also one of the messier projects, and the oil smells unpleasant. I would suggest wearing latex gloves to keep the oil off your hands.

We'll need to gain access to the top mounting nut on the struts. To do this, the trunk liner panels must be removed. Some trunk trim needs to be removed to do this. Remove the mats that lay on the bottom of the trunk.
Remove the plastic assembly covering the battery.
MB uses these plastic reusable fasteners in the trunk. This is the black plastic piece that runs along the lip of the trunk opening above the bumper. To remove this type, pry out the center piece using a small flat blade screwdriver.
Once all fasteners are removed, slowly pull out the trim piece. Use caution, because the remaining plastic pieces in the trim can pop out and go flying. Pull the plastic pieces out of the trim, and keep all the fastener pieces safely stored.
The side panels are held in place with a different type of fastener. Pull out the center plug using a small flat blade screwdriver, then pull out the plug in the panel. Remove every plug you find. Store these plugs in a safe place.
Pull off the plastic rings holding the top panel in place. They are a snap fit, and pull out easily.
All of the inner panels can now be pulled out of the trunk. If you have a CD changer in the trunk, I suggest you leave the left panel in place. It's a real bear getting that back in. We can just move the panel out of the way when the time comes. Now we have clear access to the tops of the srtuts.
If your car is equipped with ADS, carefully disconnect the acceleration sensor near the strut mounting area.
Place the 5 mm hex key into the strut shaft to prevent the strut shaft from turning, and loosen the top mounting nut. Do not remove it yet.
Now we need to lift the car. Before lifting the car, loosen the lug nuts slightly. Jack the car up and place jack stands under the car. I always place the jack stands directly under the rubber pads by the lift holes. Remove the rear wheels.
Remove the four 10 mm bolts holding the plastic cover on the lower control arm.
Gently persuade the locking tabs in the cover away from the control arm to pull the cover off.
The rear system needs to be depressurized. There is a ?? mm bleeder screw on the leveling valve. Spray some penetrating oil on it. Place a length of small diameter rubber hose over the bleeder screw nipple. Route the end of the hose into an old coffee can. Slowly crack the bleeder screw open to depressurize the system. My bleeder screw did not want to break free. I was afraid to force it, as the bracket that the valve mounts to is not very sturdy. I left it alone, and bled the system later by cracking a line open.
If your bleeder screw is seized, do the following. Mark the linkage connecting the axle to the body with a permanent marker so you can set it to the same length again. It is important that this setting is repeated, because this affects the rear ride height. Loosen the 10 mm nut on the linkage arm between the axle and the body. Once the nut is loose, you will be able to pull the self level valve arm to the DOWN position. This opens a port which allows the oil out of the rear struts. Keeping the valve arm in the DOWN position to aid in compressing the struts when the time comes.
USE CAUTION for this next step. Once the lines are cracked open, the hydraulic oil can spray out under high pressure! Let the system depressurize completely before removing the fittings. Using the 17 and 19 mm line wrenches, remove the line from the strut to the fitting on the car. This is where I ran into some trouble. The threaded portion of the line on the car did not want to turn. I ended up having to destroy the line. Do anything you can to prevent this from happening. Let the fitting soak in some good penetrating oil (not WD40) over night. Replacing that damaged line was VERY difficult.
Place a floor jack underneath the lower control arm, and raise it just enough to touch the control arm. This will keep stress off of the bolts holding the strut to the control arm. Remove the nut and bolt with a 19 mm wrench and socket. Hammer out the bolt using a brass punch and hammer.
Remove the nut at the top of the strut.
Lower the floor jack slowly, and let the control arm down as far as it will go. You may need to compress the strut to get it out. If you can't do it by hand, use the floor jack and a tool to compress the strut as shown.
Remove the strut.
I noticed that the threaded shaft in the bump stop was loose. This is a problem, as it can cause a rattling noise when going over bumps.
There is also a dense foam rubber material at the bottom of the strut inside the rubber bellows. This was deteriorated on my strut.
Install the new struts and other components in reverse order. Once everything is put back together, the system will need to be purged of air. Mount the wheels, and lower the car to the ground. Drive the rear wheels up onto ramps.
Start the car, and with the engine running, check the oil level in the reservoir. Add oil if necessary.
Move the arm on the leveling valve UP towards F. This opens the oil supply to the struts. BE CAREFUL, as the car may slowly rise up. It may take some time to see the car start to raise. Be patient. In addition, once the car does start to raise up, it does so slowly. Remember that all the lines and the struts have to fill up with oil again. Also watch out for hot exhaust pipes. Then move the arm DOWN to L. After a short time, the car should lower. AGAIN! Make sure you don't squash yourself. Keep your hands and other parts out of pinch points. Do this several times to bleed the struts of any air. Watch for leaks, and recheck your fluid level often (engine running).
Once the system is completely purged, line up the marks on the linkage again, and tighten the 10 mm nut. This will set the ride height to the proper level.
Double check that there are no leaks anywhere, and verify one more time that the oil level is at the correct level. Good Job! You're done!

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