PeachParts Mercedes-Benz Forum - View Single Post

lrg · #1 02-23-2004, 04:48 PM

I just rebuilt the rear suspension actuator valve on my 123 wagon and thought I would report for the archives. I rebuilt the valve to correct a tendancy of the rear to sag when the car was left for a day or two. The sagging was caused by internal leakage in the actuator valve (located just behind the rear differential) and was most noticable on startup when you could see the rear of the car raise 1-2" as the system pressurized. I bought a rebuild kit from the dealer ($68 and a two day order) which contains an assortment of o-rings, springs and a metal piston.

BE SURE TO HAVE BOTH REAR WHEELS SECURELY ON RAMPS AND THE FRONT WHEELS BLOCKED BEFORE ATTEMPTING THIS REPAIR.

Removing the valve is easy. First relieve any pressure in the system by briefly opening the bleed nipple on the back of the valve. Unscrew and detach the link from the actuator arm to the torque bar (if that's what it's called) that causes the lever arm to move up and down. Detach the four metal hydraulic lines at the valve, two are 11mm and two 12mm. A few ounces of fluid will drain out of the lines. The valve unit is removed by unscrewing 4, 10mm self tapping screws where the bracket on valve attaches to the car. Remove both the valve and the bracket.

The valve is split roughly in half and held together by four through bolts, two of which also hold the mounting bracket. The bolts holding the bracket are standard (14mm iirc) bolts/nuts but the two other through bolts require an 8mm hex driver. These may come off a bit hard as mine was assembled with loctite. It's a good idea to clean the outside of the valve throughly before you crack it open. Once the four bolts have been removed (note that one is longer than the others) the valve easily comes apart. Be careful to take close note of how the cam in the center of the valve is attached, it is easy to reassemble this turned 180 degrees, a detail you won't discover until you have reinstalled the valve and found it won't work (don't ask me how I know that). You do not need to remove the center shaft or the external arm that attaches to the link below the car.

On the inside of the valve you'll note a small (appx .25" across) round metal piston protruding from just off the center of the valve chamber. Carefully remove this by turning it back and forth while you pull it out. You can use needle nose pliers and it is OK to scratch the round piston if you need to as the kit contains a replacement. As you take it apart, be careful to note the location of the two springs, plunger and ball bearing. They are not under much pressure so they won'y fly apart but there is no assembly diagram with the new parts so you do need to pay close attention to how things come apart. Before you put the new piston in, you'll need to put o-rings on it. These are the two thinner O-rings that are included in the kit. Lubricate the piston with the appropriate mineral based hydraulic fluid, pull the larger of the two O-rings on to the outside groove and push the smaller of the two into the groove inside the piston. Be sure to get the smaller one in place as it is easy to miss this step. Reassemble the piston, steel ball, plunger and springs just at the old piston was assembled. There is a second, larger steel ball down in the cavity where the piston came out. This can be removed and replaced either by turning the valve body upside down or withdrawn through an access hole on the side. There is a new copper washer supplied in the kit for the small bolt you will need to remove to open the access hole. As you reinsert the new piston be sure the larger steel ball is on or near its seat, the point furthest away from the access hole. This will be pretty obvious as you look at the valve body. Again, be sure everything gets some fresh fluid on it to keep things lubricated for reassembly. The piston will go back in with just finger pressure. Replace the cam and check to be sure all the internal parts are clean before you close it up. Replace the large O-Ring on the cover and carefully press the two halves back together. It will take some pressure to get the surfaces to mate as the spring on the internal piston needs to be compressed slightly. Tighten down the four bolts and remember to remount the bracket. I used loctite on the bolts and snugged them pretty well. I could not find a torque spec. but be carefull not to over tighten.

Remount the valve on the car and reattach the 4 hydraulic lines and the link to the torque bar. Start the engine and bleed the valve a bit just to be sure everything is flushed and clean. I didn't find it necessary to readjust the link that is attached to the valve lever. My car now rides well and doesn't sag at all. This was about a two hour job and could be accomplished by anyone with a decent amount of patience and average mechanical skills.

Hope this is useful.