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Rear Self Leveling Shock Replacement
 
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Pelican Technical Article:

Rear Self Leveling Shock Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$110 to $2,500

Talent:

**

Tools:

Jack, jack stands, 19mm 17mm wrench, 17mm, 13mm, 10mm socket, Philips head screwdriver

Applicable Models:

Mercedes-Benz W124 (1986-95)

Parts Required:

New Shocks

Hot Tip:

Be prepared to catch the oil in the system

Performance Gain:

Better handling

First a little explanation of the self-leveling system suspension in the rear of the W124. The Self-Leveling System (SLS) adjusts the ride height of the rear end when it is loaded to keep the rear end at the proper level. The springs and the SLS maintain the unloaded height. The SLS maintains height when loaded by pressurizing the system which lifts the rear. The springs, struts, and accumulators work together to dampen road bumps. 

The system is made up of several parts: The Pump - supplies pressure to lift the rear; Fluid Reservoir - for maintaining fluid level; Leveling Valve - the brains of the operation, it tells the system whether to lift or lower the rear end; Accumulators (pressure reservoir) - Helps dampen the changes in pressure due to bumps on the road; Struts - Works much like a normal shock for dampening bumps but is able to be adjusted by pressure from the system to change the ride height.

The pump is always creating pressure and pushing fluid through the system. The leveling valve maintains the level of the rear end. It does this by maintaining pressure or diverting it to raise or lower the rear. When the car is unloaded and sitting at the proper ride height the leveling valve is in the neutral position. In the neutral position the struts and accumulators are still pressurized which maintain the unloaded height along with the springs. The valve maintains the neutral position pressure in the struts and the accumulators by not allow the pressure to bleed off and also directs the pressure that the pump creating to back to the reservoir. When a load is put into the back, the lever arm on the valve is deflected into the fill position which diverts the pressure and fluid flow to the struts and accumulators. This pressure expands the struts which lift the rear until the lever arm is in the neutral position again, a check valve in the leveling valve keeps the increased pressure from bleeding off until the arm is deflect into the return flow position. When the load is removed, the arm on the leveling valve is moved to the return flow position which allows the increased pressure in the system to drain off, until the valve returns to the neutral position and the rear of the car to its normal unloaded ride height.

Failures and symptoms can be: Pump failure - Rear doesn't rise when loaded; Leveling Valve failure - The rear settling or sagging after sitting for many hours, and in extreme cases the rear doesn't rise when loaded; Accumulator failure - Rides bouncy and/or hard, rear bouncy like when you have bad shocks; Strut failure - Rides bouncy but not hard.

Many of the problems that arise in the SLS are caused by leaks, so the main thing is to look for leaks. Leveling Valve - This valve is located just in behind the rear axles and differential, slightly on the driver's side. The valve can leak internally; in this case you won't see fluid on the valve. It can also leak so there is visible moisture on the outside of the valve. Please see our article on replacing your leveling valve. Accumulators - Diagnosing this isn't easy; the accumulators have a rubber bladder in them, with suspension fluid on one side and gas on the other. They can get holes in the rubber and then the fluid gets into both sides and the accumulator is shot. By poking the eraser end of a pencil into the accumulator you can feel around the diaphragm for a tear. The pencil should only go half way into the accumulator. If there is a tear in the diaphragm you'll be able to poke the pencil all the way in. Struts - Struts aren't often the source of problems with the SLS, they rarely go bad. But when they do the usually start to leak, so they will have suspension fluid on them and they shouldn't. Pump - The pumps general don't break they usually start leaking. They leak internally usually, and cause one of two things to happen. They allow engine oil to be introduced into the SLS system, or they allow the SLS fluid to go into the motor oil. If the SLS fluid in the reservoir is black it has motor oil in it, or its really old fluid. Either way it should be changed. If you keep losing fluid but it's not leaking anywhere else then it is going into the motor oil. Either way you've got to rebuild the pump. There are kits available for this. The other thing that can happen associated with the pumps are the hoses. There is one going from the reservoir to the pump and one going from the pump to the leveling valve. Make sure they aren't leaking. The one going to the valve is high pressure so if it gives out you'll have a big mess on your hands.

If your shocks need to be replaced, begin by safely raising and supporting your car off the ground. Please see our article on jacking up and supporting your Mercedes-Benz. Next remove the rear wheels. Remember to loosen the lug nuts while the car is still on the ground.

The fluid reservoir for the self-leveling system is located at the front left of the engine compartment beside the ABS pump.
Figure 1

The fluid reservoir for the self-leveling system is located at the front left of the engine compartment beside the ABS pump. The shocks and lines will leak out fluid when you remove the shocks so be sure to check the level and replace any lost fluid.

The shocks (yellow arrow) connect to the lines from the leveling valve (red arrow) via a rubber hose.
Figure 2

The shocks (yellow arrow) connect to the lines from the leveling valve (red arrow) via a rubber hose.

Use a 17mm and 19mm wrench and break the connection for the line.
Figure 3

Use a 17mm and 19mm wrench and break the connection for the line. NEVER do this with the motor running. The system will be under pressure so make sure to wrap the lines to protect the vehicle and yourself from spray and be prepared with a container to catch the fluid. Dispose of the fluid according the regulations in your area; do NOT pour it down a drain or in the streets.

Remove the plastic lower control arm cover.
Figure 4

Remove the plastic lower control arm cover. It is connected by two 10mm bolts (red arrows) and plastic clips on each side (yellow arrows).

Support the control arm with a jack or place the wheel back on the ground.
Figure 5

Support the control arm with a jack or place the wheel back on the ground. The shock will be under tension when you remove the bolt from the tower and you need to support the tension so the control arm does not spring downwards when the shock is released.

Get access to the top of the shock.
Figure 6

Get access to the top of the shock. In the wagon you will lift up the rear seat and remove a single Philips head screw (red arrow) from the side trim.

Use a 13mm socket and remove the bolt on the top of the shock (red arrow).
Figure 7

Use a 13mm socket and remove the bolt on the top of the shock (red arrow).

Remove the bolt, washer (red arrow) and the rubber mount (yellow arrow).
Figure 8

Remove the bolt, washer (red arrow) and the rubber mount (yellow arrow). Check the condition of the rubber mount and replace as needed.

Slowly lower the jack or raise the car.
Figure 9

Slowly lower the jack or raise the car. Remove the two 17mm bolts (red arrows) using two 17mm sockets or wrenches.

You can now safely remove the old shock form the vehicle.
Figure 10

You can now safely remove the old shock form the vehicle. Installation is the reverse of removal. Do not forget to replace any lost fluid to the system.


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Comments and Suggestions:
Windsorhayseed Comments: Thank you to Montana. I looked for a while trying to figure out where that darn filter was, his instructions were right on and saved a bunch of agitation. I am new to Mercedes and bought my wife a 2000 wagon. His instructions were spot on and easy to understand.
October 16, 2016
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Montana Mercedes Comments: I used this article to replace the SLS shocks in my 1998 Mercedes E320 rear wheel drive wagon. It has 157,000 miles on it. I was getting a mysterious clunk when I ran over bumps. Plus the body swayed excessively on curves. I read that the clunk comes from a worn out ball joint in the shocks.

The only difference between this article and my car was in locating the upper shock 13mm bolt. On the wagon it was behind the carpeted panels that sit between the rear seat and the spare tire panel. I had to take two posi-drive bolts out of two D ring floor anchors on each side. The plastic cover caps pop off with a small screwdriver. One D Ring anchor also held a seat belt anchor bolt. Then I removed the "clip on" spare tire panel. Removed two large Phillips head screws that held the other panel in place. That allowed me to pull the panel out enough so I could get a socket wrench on the rear shock top bolt.

A couple of cautions:
I lost a shock top washer and a rubber donut when removing and/or installing the shock. They fell into a body cavity by the top of the shock. Fortunately the shocks came with new washers and donuts. I sprayed the inside of the donut with WD-40 so it would slip nicely onto the short shock top shaft and allow me to hand start the 13mm top bolt.

Both shocks leaked hydraulic fluid and had caked fluid and dirt covering the bottom half of each cylinder. One hydraulic line had a rusted nut which rounded when I tried to loosen it. Pelican got me a new hydraulic "C" line for $25.00.

When I drained the hydraulic fluid from the driver's side it was creamy white and foamed. That side also had the rusty nut and I am assuming that water got in the leaking shock. So I drained all of the hydraulic fluid and replaced it, 1 quart, with genuine Mercedes fluid.

I also replaced the hydraulic fluid filter in the under the hood reservoir. A spring holds the filter in place via a hooked loop that connects to a drilled tab in the reservoir cap. Compressing the spring and twisting it will release the old filter.

Lastly the lower twin bolts that held my shocks in place were 5/8 bolts; not 17 mm. The new shocks came with new bolts which were 17mm. I used blue thread locker on all nuts.

It took me about 2 hours per side to replace the rear shocks. I am a home mechanic with a reasonable collection of tools.

It would be nice if Pelican reproduces this article and makes it available for 1998 E320 Wagon owners. I only found the original article via Google.
May 31, 2016
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 

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