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self-levelingValve Rebuild
 
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Pelican Technical Article:

self-levelingValve Rebuild

Steve Vernon

Time:

4 hours4 hrs

Tab:

$10

Talent:

***

Tools:

17mm, 10mm wrench, 11mm flared nut wrench, pick

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

O-rings, hydraulic fluid

Hot Tip:

Keep everything really clean

Performance Gain:

Working self-leveling suspension

Complementary Modification:

Check your CV joints

The self-leveling rear suspension on some W123 models can seem like a bit of a dark art to those who have not had the chance to learn it. Once you know the system, it is not all that difficult to understand or work on. Please see our article on understanding the self-leveling suspension to give you more information on the different components.

One of the main problems with the leveling valve on the rear of the vehicle is that it will over time start to leak and eventually affect the performance of the system. If your leveling valve is leaking or not functioning correctly you do not need to take the car to a dealership that will charge you a fortune to replace or rebuild it. Thanks to Peach Parts member Biodiesel300TD you can follow these step by step instructions to overhaul your own valve.

You will need to safely lift and support the rear end of your W123, please see our article on raising and supporting your vehicle.

Over the years your car may have been serviced by multiple people including previous owners and this can lead to parts replaced with different size fasteners and hardware. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches. If something is different on your vehicle please let us know and share your info to help other users. If you have any questions or comments or even a different procedure you would like to share please leave it below and please leave your vehicle information.

The self-leveling arm and unit is attached to the rear sway bar behind and off to the left side of the rear differential (red arrow).
Figure 1

The self-leveling arm and unit is attached to the rear sway bar behind and off to the left side of the rear differential (red arrow).

You are going to be working with hydraulic line fittings so make sure that you have the right tool; that tool is a flared nut wrench.
Figure 2

You are going to be working with hydraulic line fittings so make sure that you have the right tool; that tool is a flared nut wrench. The wrench is designed to grasp five sides of the soft fittings and keep them from stripping or rounding. Due to the type of hard lines used, if you round or strip one of these fittings you may end up replacing the whole line.

With the car jacked up and properly supported, remove the hydraulic lines shown in the photo below.
Figure 3

With the car jacked up and properly supported, remove the hydraulic lines shown in the photo below. You'll need an 11mm flared nut wrench. Be ready with a catch pan, you may lose a few quarts of fluid. Make sure on the supply and return lines you use a 17mm wrench to hold the big connections on the valve, you don't want to remove those, only the hydraulic lines that thread into them. Once the hydraulic lines are disconnected remove the 10mm nut holding the lever arm to the rod.

With the hydraulic lines and lever arm disconnected, remove the two nuts and bolts shown in the photo below.
Figure 4

With the hydraulic lines and lever arm disconnected, remove the two nuts and bolts shown in the photo below. Do not take the other two out yet. They hold the two halves of the valve together. Once the valve is removed from the car, clean all the grime and buildup off the valve so you don't get any of it in the valve when you take it apart. Make sure the holes where the hydraulic lines go are kept clean, and plugged so nothing get into them either.

Now remove the two bolts holding the two halves of the valve together.
Figure 5

Now remove the two bolts holding the two halves of the valve together. Then carefully pull the valve apart. Pay close attention to the way things come apart, it will make re-assembly easier. In my experience the cam sticks to the side of the valve with the O-ring, so that's probably where yours will end up. With the two halves apart, remove the old O-ring and clean up the sealing surface. Make sure any solvents are cleaned off, and then put in the new O-ring. O-ring #1 seals the two halves of the valve together.

Remove the cam from the valve and set it aside on a clean rag.
Figure 6

Remove the cam from the valve and set it aside on a clean rag. Then gently pull the piston out of the valve. It can be stuck in pretty tight depending on the condition of the O-ring inside so be careful that you do not lose any parts. There are two steel balls inside the valve, a small one and a big one, do not lose them.

Separate and clean each part of the piston assembly.
Figure 7

Separate and clean each part of the piston assembly. The photo below shows the order they go together, and where O-rings #2 and #3 are located. Carefully remove the O-rings, make sure not to scratch anything. Clean the sealing surfaces and put in the new O-rings. It may also be helpful to give the whole piston a light coating of suspension fluid to help prevent any binding when putting it back into the valve. The small steel ball goes inside the inner piston then is followed by the small spring. The large steel ball floats back and forth in the channel at the bottom of the hole where the piston assembly goes, and should be located toward the center of the valve. O-ring #2 seals the inner piston to the outer piston. O-ring #3 seals the outer piston to the body of the valve.

Here is a schematic of the valve that might help you assemble the piston assembly.
Figure 8

Here is a schematic of the valve that might help you assemble the piston assembly. 3d is the small steel ball, which is inside the piston assembly. 3f is the large steel ball, which is in the channel at the bottom of the hole for the piston assembly.

To get to O-rings #4 and #5 you will have to remove the rod that goes through the body of the valve.
Figure 9

To get to O-rings #4 and #5 you will have to remove the rod that goes through the body of the valve. Before you remove the lever arm from the rod, index the end of the rod and the lever arm so you can put them back together in the same orientation they originally were. Then loosen the nut and remove the lever arm from the rod. With the lever arm off you can pull the rod out from the inside of the valve. NOTE: Some of the early 123 leveling valves only have one O-ring instead of two. If this is the case on yours just replace the one and save the other. O-rings #4 and #5 seal the lever arm to the body of the valve.

Proper placement of the cam and alignment with the lever arm is key for the valve to work right and sit level when unloaded.
Figure 10

Proper placement of the cam and alignment with the lever arm is key for the valve to work right and sit level when unloaded. After replacing O-rings #4 & #5 put the rod for the cam and lever arm back into the valve. Put the cam onto the rod so it is lined up as in the diagram below. You'll also have to pay attention to which way the rod is rotated. You need to have the notch on the rod for the bolt on the lever arm in the right location. Once you have the cam on and the notch in the right place you can put the lever arm on, and use a 4mm diameter locking rod to assure that the lever arm is in the correct place. Now you're ready to put the halves of the valve back together. Once the valve is back together re-install it back into the car. Be careful when you thread the hydraulic lines from the accumulators back into the valve. The valve is aluminum and if you cross-thread your connections you will be looking for a new valve. Thread them in by hand and make sure they aren't cross-threaded before you tighten them with a wrench. You will need to refill the suspension fluid reservoir. The system is self-bleeding so you won't need to do any bleeding. Start the car and look for leaks. If there are no leaks shut the car down and have a large helper or two child size helpers sit in the back. Then start the car and watch to see if the rear end lifts up like it should.

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