ABC Valve Block Rebuild

So, you walk out to your car one morning and one corner has dropped all the way to the ground. Great. Join the club. As most of these cars are now nearing or above 100k miles, this is a common occurrence. The good news is that the fix is relatively easy and inexpensive.

Another S600 with ABC issues
Front corner drop – bad valve block


If you haven’t already, check out the ABC suspension troubleshooting article. This will give some insight to the system and how everything works. This article is purely a guide to rebuilding the factory valve block. Every rebuilt valve block you find on eBay or anywhere else is rebuilt this same way. All they do is replace the o-rings. It is not a complicated or expensive procedure. We do the same thing here in the shop.

Portions of this page were originally written by user “knowbenz” on the mbworld forum. I’ve used some of his photos and modified the text of his write-up.

“Book time” to remove and reinstall the front valve block is 2.4 hours.  The rear valve block is 1.3 hours. To clean the block I would add another hour. I would definitely add another 2 hours if this is your first time doing the job, especially up front. Things can be tricky to get to if you don’t have the right tools.

I would HIGHLY suggest that before you replace the valve block that you remove and replace 5 liters of fluid from the ABC system as well as flushing the system through a new filter. If your valve block failed, it failed from debris in the system. You need to get it out. I really recommend a 10 liter flush.



10 Liters of Pentosin CHF 11S. This is exactly the same as Mercedes part number: Q1320001
I like to buy the 5 liter on eBay for $65/ea.
Two filters: MB part number: 0031846101 – #36/ea on Amazon


O-rings – order from APG (, and “The O-Ring Store” (

  APG part #   Cross-Section   Inside Diameter   Outside Diameter   Height   Quantity per block
H90018 .070 7/8  (0.739) 1 1/16 4
H90016 .070 5/8  (0.614) 3/4 1/16 6
H90015 .070 9/16 (0.551) 11/16 1/16 2
H90014 .070 1/2 (0.489) 5/8 1/16 4
H70013 .070 7/16 (0.426) 9/16 1/16 4
There are also some spacers that may need replacement – (Buna-N 70 square cut o-rings)
They are APG part numbers SH70013, SH70014 , SH70015 , and SH70016. One set per block.

Do NOT use Harbor Freight o-rings like is suggested on some forums. I say this not because they aren’t durable but because tolerances on them are poor. Some o-rings are slightly larger than what they should be and these valve blocks have SUPER tight clearances. This causes the o-rings to twist or pinch and they leak by, causing the same issue as before.


Take some time beforehand and do as much of a flush as you can on the ABC system.

Open the reservoir and remove the filter. The line that runs into the cap and filter is the return line. When you start the car, fluid will come out of this hose. There are several ways to do a flush and I will leave it up to you to figure out but essentially, take that return hose off of the cap and secure it into a bucket. Have a friend in the car. With the lid off of the reservoir and everything clear of all moving parts have a container of Pentosin ready. Have your friend start the car. Fluid will start to come out of the hose and into your bucket. It is your job to watch the level of the reservoir to make sure it doesn’t run dry. Just keep it filled. Level is not at all critical here, just make sure it doesn’t go dry. You can over fill it all you want. When the fluid starts to come out clear (You can choose to do a 10 liter or 15 liter flush, most of the time 10 is good enough), you have done a decent job and can stop topping off the reservoir. When the fluid gets pretty low in the reservoir, shut off the car. This reduces the amount of mess you make when changing the valve block. If you do suck in a little air, it isn’t the end of the world, it should come out on it’s own, but do not suck in a lot of air. Do your best to keep it from getting any. Keep enough fluid left over to refill the reservoir after the valve block installation. There will still be some dirty fluid in the struts and some other areas but this is a decent job for now. Install the new filter and leave it be while you do the valve block.


The first thing you need to do is get the front valve block out of the car. You will need to lift the car up and remove the front wheels. You need to remove the front left wheel for access. You will also need to remove or support the front right wheel because once you remove the valve block, you will remove the isolation valve and the weight of the assembly will pull down on the strut dust cover and pull it out of the top retainer. This isn’t a huge deal as the car will still be drive-able but it will shorten the life of your strut since it will be exposed to dirt, dust, and road grime.

MAKE SURE THE VEHICLE IS SUPPORTED BY THE LIFT POINTS ON THE CHASSIS BEFORE TOUCHING THE VALVE BLOCK!!! Do not use the control arms to lift the vehicle and do not use ramps. When the valve block is removed, pressure is released from the system and the suspension will drop the car to the ground. Make sure the car is properly supported by the lift pucks on the car. Now is also a good time to mention that those lift pucks get ripped off all the time. The good news is that they are very inexpensive and take 30 seconds to install. Mercedes part number: 0019979586 $10 each on eBay, cheaper if you buy pairs or a set of 4. 

This is a photo from Pelican Parts of I think a 190E jack points. This is a completely different Mercedes but they all look the same. On your rocker panels you will see two cutouts for the factory jack. The jack points are located under them, as shown in this photo. If your car is missing the jack pads, it will just have a round hole in the metal under the car. The car is still safe to jack up but watch out that you don’t catch the plastic rocker cover with the jack or you will damage it.


Once the wheels are removed, go ahead and remove the acoustic panels from under the car. You will need to remove the middle panel first, then the front panel, under the radiator. Take this time to also remove the front left fender liner. I also take a couple minutes to remove the front bumper. The front bumper on these cars is easily scratched and removing it opens up more access, so why not. It is only 6 easily accessed bolts and a couple of bulbs to remove. The headlight comes out as well with only a couple of bolts and makes access and visibility to the valve block much better. If this is your first time doing this job, removing these two items will make your life MUCH easier. Things are very cramped in the valve block area and there is a mess of hydraulic lines running everywhere. It’s one of those things that if you know what you are looking and feeling for, it’s easy to do it blind, but if you don’t know what you should be finding and exactly where everything is located, you will spend a lot of extra time messing around. Just take off the bumper and headlight.


This is the official repair procedure.





Here is the valve block out of the car. The small valves (on top in this photo) are the isolation valves. These are the ones that will cause the issues of the car sagging overnight. Some people choose to leave the actual control valves alone. I recommend rebuilding them all at the same time. The hard work is getting the valve block out. Removing all the valves also allows for a better cleaning of the actual aluminum block.

First step is to remove the plastic clips that hold the valves together. How I usually do this is to release one tab on one valve and turn the valve out of position so I don’t have to fiddle with two sides at once, the turned side will be off of the lock tab that holds the clip in place. Here is an overhead view, notice it is only slightly turned. If you turn it too much it will be difficult to remove the clip. These clips are VERY brittle. Use care not to bend them any further than necessary. I personally like to use two sets of channellocks with the block in a vise, careful not to squeeze any more than is absolutely necessary. The clip will slide up and out without having to rotate the valves. It doesn’t matter how you do it, just be careful not to break the clip. They are VERY brittle.

Once it is slightly turned I use a small screwdriver to push the clip out of the way and place another small screwdriver under the base of the clip to put a little pressure upwards


From there I leave one screwdriver underneath the clip and then loosen the clip on the other side of where that screwdriver is. once you push the clip off the lock it tends to move up and then I put the little screwdriver underneath and work it up from side to side

Do the same for the other pair of valves. For the locking valves I use my hand for the upward pressure as the clip is in the middle of the valves. From here you can rotate the valves 90 degrees on the control valves and about 45 degrees on the locking valves and then they can be pulled out of the valve block.

The big O-rings at the base of valves just seal outside moisture and such from getting in, They are not under hydraulic pressure so if they look a little dry it’s OK. They do not need to be replaced.

Take the plungers and springs out of the valves. Now you can clean everything. Do this on a clean surface so you don’t introduce any dirt or dust to the system. Treat these as if they were inside your transmission. ANY dirt will cause trouble. Now is a good time to toss the block itself and the plungers into an ultrasonic cleaning solution if desired. If you don’t have one, just clean it as best you can by hand. Be VERY careful not to scratch the aluminum.

Inspect the white teflon spacers for any kind of damage, these rings don’t offer any sealing, they mainly offer support to the sealing O-ring to help keep it in place. If they are damaged they can be replaced with rubber o-ring. The rings on these valves were in good shape so They just got a good cleaning with a tooth brush and a little solvent.


Here is a few pictures of the valves with their respective seals that will be getting installed after the valves receive a thorough cleaning. I didn’t take pictures but I always like to apply power to the control valves in both directions and run solvent both ways through the passages just incase some gunk is caught up inside the valve. Also be sure and thoroughly clean the aluminum housing to get all old fluid and debris out of it.



After it is all cleaned up and new O-rings installed it’s time to put the valves back in. I use plenty of new hydraulic oil to lubricate the valve with o-rings as well as the valve block itself. Take your time putting them in to ensure you don’t pinch an o-ring.

Once all valves are in place it’s time to put the clips back on. Simply push the clips in between the valves and down into position.

Double check you have 14 old o-rings and no new o-rings on your workbench. After that put the valve block back in the car.



Once the valve block is reinstalled, get your wheels back on, set the car down, and top off the ABC fluid. Be CAREFUL. When you lower the car, it will go all the way to the ground. There is air in the struts from taking off the valve block. You do not need to do anything special to bleed the system. Start the car. Let the car run for a few seconds and keep an eye on the ABC level. I fill through the dipstick hole so I don’t have to shut the car off. Keep it topped off. Once it stays level, which shouldn’t take more than a few seconds, go ahead and use the “raise car” button on the dash. Raise the car up and down about 15 times, waiting for it to settle at the top and bottom of the range. The first several times you will probably not notice the car moving at all. This is normal. Just keep fluid level high (I always fill right to the top and then just adjust level after. It saves a few trips back and forth). Now you are done. Check for leaks and reinstall all the acoustic panels and other components removed.

Go for a drive and play with the raise car button a bunch. Your goal here is to push as much fluid through the new filter as possible in a short amount of time. Hit bumps. You want to force the dirty fluid out of the struts. Once you have completed a decent drive, go back, shut the car off, and swap in a new filter. Now you are good to go for some time!