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lrg 02-23-2004 04:48 PM

Wagon rear suspension valve rebuild
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.


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.

Rick Miley 02-23-2004 05:17 PM

If I remember correctly, people have posted that there was no rebuild kit available. So a part number for that kit might be a welcome addition to the post.

lrg 02-23-2004 05:58 PM

Excellent point!

Part# 000-586-00-32

Part is listed as a "Washer Set" and according to my invoice the list price is $70.76.

1983 300TD 06-14-2005 08:50 PM


These instructions are fantastic- a must read for anyone doing this job. I just rebuilt my control valve last night, and things went quite well all in all. However, I did manage to crack one of the hydraulic lines while taking it off. :o So tomorrow the wagon goes in to my new local, favorite indy to splice in a new piece of metal line. I could flare a new piece in myself, but I'm rewarding myself for all the work I've already done! :)

I do have one question, though. There are five o-rings included in the rebuild kit. The above instructions tell you to use 3 of them, which I did. What are the other 2 for? I looked everywhere and couldn't find where they could possibly go. :confused: thanks

lrg 06-15-2005 12:06 AM

As I recall I did the same. As much as I looked I couldn't find a spot for the extra parts and as you undoubtably discovered it's a pretty simple valve so I think I(we) would have found it. My guess is that the rebuild kit is intended for more than one type of valve (it's far cheaper for MBZ to inventory one kit as opposed to two) so depending upon which valve you're rebuilding there are parts left over. My rebuild still works like new.

Glad the job went well.

JimmyL 06-15-2005 12:22 AM

What a great write-up, and very useful info for those of us with wagons. My '80 SLS works fine, but the '85 doesn't. I haven't checked a thing, other than adding fluid and replacing the low pressure hose. (yes, sadly in that order)
Now, would the next person that does this rebuild take pictures. Excellent instructions, but a lunkhead such as myself always benefits from pictures.

1983 300TD 06-15-2005 06:51 PM

I've got problems.

I got the hydraulic line fixed. Put fluid in, bleed the line, got fluid to move from the resivoir to the back of the car. The back of the car moves up and down when manually moving the actuator. But it does not seem to respond to any sort of load, and it's sitting really, really low in the back. Another detail, IRG, remember when you said that the one piece that connects to the cam can easily be turned around? I'm starting to doubt myself...

When you implied that you had turned that piece around yourself, did the valve work at all? I would like to eliminate that possibility ASAP. I'm going back to the garage for some more frustration. Any help appreciated. Thank you :(

lrg 06-15-2005 07:07 PM

It's been a while since I did it but IIRC it would work but only if I made pretty extreme movements of the valve lever. If you think about it the valve should work with only a relatively small movement of the lever since the torsion bar itself doesn't move that much. If the valve only works with a substantial (say 1-2" movement) of the arm then you probably have the cam in backwards. Also, if you do a reassembly be sure you got the large ball bearing on the correct side if the piston so it can seat itself properly. You should be able to see it if you open the access hole that has the copper washer.

I have to admit that I suspected I had the cam on 180 degrees reversed as I had an Uh-Oh! moment on reassembly when I realized it was possible to install it two ways and I'd paid too little attention when disassembling to know what was right. The good news is that the job went much quicker the second time. :rolleyes:

1983 300TD 06-16-2005 01:15 PM

It's funny how that works. I was trying to be careful to such a degree that I went full circle and hit carelessness. Sure enough, I had that stupid part in backwards. :rolleyes: And yes, it does come apart faster the second time. ;) So the valve is in working order again. However, I think I have some tweaking to do with the linkage to get it to maintain the ride height I want.
Question...have you ever had your control valve make a "eeeeeeeeeeeee" sound? Mine only does it, that I can tell, when it is as high as it can possibly go. Almost like it's hit it's high point but it's still trying to push thru it. This noise is the main reason why I rebuilt the valve, and now it's still doing it. Any ideas? Thanks again for the awesome instructions IRG.

When you crack the valve open for the first time, make sure you remember how a somewhat circular piece of metal attaches to the cam that spins it. Otherwise, you will ruin your day, like I did yesterday, when you think you're all done and reinstall it, only to have it kick you in the rear. :)

lrg 06-16-2005 02:42 PM

It sounds like there's a pressure relief valve that is making some noise when the shocks extend fully and the pressure is getting bled off. I assume the noise is coming from the valve. I've not had that problem but it doesn't sound too serious. My problem with the SLS valve, and the reason I rebuilt it, was to eliminate the sagging rear end. Glad you solved the assembly problem. It's amazing how easy it is to get that cam reversed (and how often a 50-50 probability can go against you).

peterhardie 09-29-2006 09:36 PM

the other 2 o-rings...
...belong to the valve lever shaft, along with the lock washer included in the kit. If you open up the valve, pull off the cam, AND unbolt the lever arm from the shaft, you can push the shaft out. Looking in the shaft hole from the outside of the valve casing, you will see two seals in undercuts. I got them out with bent picks, the used the shaft itself as a stop to help put the new ones in, needing a straight pick.

I weighed doing this at all, since it was not leaking , but the difference in tension was noticeable with new rings, so I am glad I did.

Feeling good about figuring that out did not stop me from screwing up. After making very sure to watch the orientation of the cam, while doing the shaft o-rings, I re-inserted the shaft 180* off (there is a relief in the shaft for the set-lock bolt, so it needs to go back the same way it came out. I oops'ed that.)

I found all this out when I put the valve back in the car and got the tail to rise and fall only with the lever pointing toward the back of the car. SO..... I have to remove, disassemble valve, pull shaft out and reinsert 180*.

A pictorial would really be helpful for first-timers on this. When I disassembled, everything flew apart, and I had to figure out what went where. As well, memory does not always serve perfectly. I was still saying prayers after the thing was bolted together. Anyone seen a pictorial guide to this?

Anyway, my wagon rear is sitting high and pretty. Yeehaw! Time to put the 15"s on!

peterhardie 10-04-2006 06:02 AM

pictures and explanation

That is the pdf site for the suspension containing all the pics you need to disassemble and re-assemble. Those of you with the manual on CD should look at the section Level COntrol 501 "functional description" to find the same thing.

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