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HOW-TO: Replacing C126 Rear Hydro-Struts (cars with rear SLS)


Site Honcho
Staff member
Introduction and Background

The 560SEC and 560SEL in US spec share with the 500E/E500 a rear SLS (self-leveling system). The components of the system are different, but overall the system operates on a nearly identical principle.

One of the "wear" components of the C126 SLS are the rear hydro-legs (aka "struts"). These struts operate under hydraulic pressure, driven by the radial piston pump attached to the front of the engine block on the driver's side. The hydro-legs have a large ball joint at the bottom, where they mount via two-bolts to the rear trailing arms ("rear control arms") on the rear suspension. With time and use, these ball joints can and do begin to get loose and sloppy, resulting in a noisy "clunk" that emanates from the rear suspension, particularly over rough surfaces and bumps.

This is a very similar condition as found on the 500E/E500 models. A separate HOW-TO on replacing the 500E/E500 hydraulic struts, specific to these models, can be found at this link.

Job Overview

Each rear hydro-leg is attached to the car via one single nut at the top, behind the rear seat of the coupe/sedan, and two bolts that are attached to the bottom of the rear trailing arm. The hydro-strut fits inside of the coil springs, and is removed by dropping downward out of the car.

The hydraulic line attached to each hydro-strut via a banjo fitting also must be removed. This necessitates releasing the pressure in the SLS system at the rear level control valve, and catching any and all SLS fluid in a drain pan.

Working on both sides of the car underneath also provides an excellent opportunity to inspect critical components, including the following systems:

  • Fuel system - fuel hoses, pumps, accumulator, filters - check for leaks, seepage, weak lines, bad connections, etc.
  • Rear flex disc - check for obvious cracks and wear
  • Rear driveshaft rubber boots - check for tears, cracks and other damage that would necessitate replacement
  • Rear brake pads and rotors - check for wear on both
  • Rear suspension components - check for anything that appears abnormal or irregular
The MB hydro-legs are quite expensive, and are made by Sachs-Boge. Thankfully, Sachs makes an equivalent hydro-leg (Made in Germany) that is sold on the aftermarket for considerably less money than the MB model. These can be purchased from AutohausAZ or other quality aftermarket parts vendors.

Job Requirements

The following parts are REQUIRED for this job:

Rear hydro legs - Mercedes-Benz part number 126 320 48 13

It is also a good idea to replace the rubber bushings that mount the top of the hydro-legs to the car's body. Two of each of these rubber bushings are required:

Top bushing -- 114 326 00 68
Bottom bushing -- 115 326 16 68

I also replaced all of the retaining washers (upper and lower) and per the EPC (although my car did not have these), the spring washer that is found at the very top of the struts.

Also, for the hydraulic lines where they attach to each of the rear hydro-legs, four copper washers are required at the banjo bolt connections. These should NOT be re-used -- you must buy new ones. The MB part number is XXX XXX XX XX and four are required. Luckily, I had many of these in my parts stock.

The following tools are required, or at least highly advised:

  • Medium or stubby flat-blade screwdriver
  • 3/8" ratchet with short or medium 3/8" extension
  • 17mm socket, 3/8" drive
  • 17mm open-end wrench
  • Small crescent wrench
  • Lug wrench
  • Floor jack
  • Jack stand (for safety)
  • Wheel chocks (for safety)
  • 1/2 can brake cleaner
  • drain pan
  • large piece of cardboard (flattened shipping box is good)
  • 1 liter MB or quality aftermarket hydraulic fluid (SLS fluid)

Getting Started

First of all, park your car in a safe place to work on it. Put it in park, but don't apply the rear parking brake. Chock the front wheels of the vehicle so that it cannot roll while the vehicle is elevated.

Next, loosen the rear wheel lug bolts of the side you are working on. After that, elevate that side of the vehicle with the floor jack, raising the bottom of the tire off the ground. For safety, place a jack stand under the rear of the car to support the vehicle while you are working on it. Leave the floor jack in place as extra security, if possible/plausible.
IMG_7071.JPG IMG_7072.JPG

After that, remove the lug bolts the rest of the way and remove the wheel from the vehicle.
IMG_7073.jpg IMG_7074.JPG

Check the tire for wear. As you can see, my Continental ExtremeContact DW tire is down to the wear bars, so it will get replaced this winter. Cool to see the branding molded into both the rain channels and tread of the tire.
IMG_7075.JPG IMG_7076.JPG IMG_7077.JPG

After removing the wheel, visually check the brake rotor and pads on that side. The photo below shows me checking the rotor wear with my fingernail. If there is a significant lip (and my rotors are right on the border of this) that you can "catch" with your fingernail, they you should replace the rotors soon. In my case, that will be a job for another day.

The next thing to do is to remove the rear seat for that side on the coupe. This is easy to do and takes just seconds. Sets the seats aside - perhaps give 'em a slathering of Leatherique or other leather-care creme to help keep them moist.

After removing the seat on that side, carefully fold back the insulation sheet toward the center of the car. You will see the amplifier for the stereo speakers on that side of the car exposed in its mounting bracket, as well as two plastic covers behind and below the amplifier.
IMG_7080.jpg IMG_7081.JPG

Swivel the amplifier out of its bracket and set it aside. You can let it dangle by its wires, or you can unplug it if you wish. In my case, I just left it dangling to the side.

Use your fingernails or the small flat-blade screwdriver to prise up the plastic covers behind the seat.
IMG_7083.JPG IMG_7084.jpg IMG_7085.JPG

Here are images of the compartments, with the caps removed. Note the hydraulic line attached to the top of the strut.
IMG_7087.jpg IMG_7088.jpg

At this point, you need to loosen the top nut at the rear struts in the round hole you just exposed. Because tension needs to be placed on the shocks at the time of loosening so that the tubes inside don't turn while you're loosening the nuts, there are two ways you can do this:

1) BEFORE you jack the car up in the earlier step to remove the tire, loosen each of the shock bolts while the car's wheels are on the ground; or

2) AFTER you jack the car up, and remove the rear tire, place your jack under the rear trailing arm (rear control arm) and jack it up a few inches, to place tension on it.

Then, whichever method you choose, you can remove the top nut from the strut. I used a small crescent wrench as a counter-hold on the top of the shock tube -- it has two parallel surfaces that you can use for this purpose. Using your 17mm open-end wrench, loosen the nut and remove it. Then carefully remove the top washer, spring washer (if present; my car didn't have one as the EPC diagram shows it should have had). Then use a small flat-blade screwdriver to prise up the top rubber bushing, and set the parts aside. These steps are illustrated below.
IMG_7099.JPG IMG_7100.JPG IMG_7101.JPG IMG_7103.JPG IMG_7104.JPG

The next step is to release the hydraulic pressure in the system. Probably the easiest way to do this is to get a large piece of cardboard and an oil drain pan, and place them underneath the hydraulic self-leveling valve at the rear axle. Loosen one of the lines going into the valve and release the pressure, and let whatever fluid flows out, go into the drain pan.

While this draining action is happening, take your shop light and shine it around underneath the car. Carefully examine the rubber parts around there, including the rubber exhaust hangers, the rear flex disc, the fuel pumps and lines (checking for leaks), the rear brake lines, the rear axle boots, and the sway bar mounts.
IMG_7092.JPG IMG_7093.JPG IMG_7094.jpg IMG_7090.JPG

Not a bad idea to check the condition of the rear differential mount, too. As you can see, mine is old and pretty marginal, and in need of replacement. Thankfully I have a spare factory MB rear diff mount in my parts stock, so I will replace this with another HOW-TO article in the near future, along with the rear sub-frame mounts.

Next, move your drain pan and cardboard under the car, to the location directly underneath the rear trailing arm. Inside the car, with your 17mm 3/8" socket on a short extension, loosen the banjo fitting at the hydraulic strut. It's going to let loose with some hydraulic fluid, so you will want your drain pan underneath to catch the fluid. Let it drain as best you can, and wipe things up afterward with a rag soaked in brake cleaner. There should be two copper washers on either side of the banjo connector. DO NOT re-use them; replace them with fresh washers.
IMG_7095.JPG IMG_7097.JPG IMG_7098.JPG IMG_7096.JPG

After removing the hydraulic line's banjo connector at the strut, then you can go ahead and remove the bottom connection of the strut at the rear trailing arm. The lower part of the strut is connected by two 17mm bolts. You can loosen these bolts with a 17mm 3/8" socket with no extension for better leverage. They are on their pretty tight, so it may take a bit of muscle power to remove them!

Once both bolts are removed, CAREFULLY lower the strut down through its hole in the rear trailing arm, and lift it away from the vehicle.

Here are a couple of side-by-side photos of the original and replacement struts.
IMG_7107.JPG IMG_7108.JPG



Site Honcho
Staff member
After removing the old strut, you need to prepare the new strut for installation back up into the vehicle. To do this, remove the old bottom washer and bottom rubber bushing from the top of the old strut. There's a high probability that the old rubber bushings are shot and smashed down (particularly the bottom one, as you'll see in a minute) and they will need to be replaced. Since the rest of the hardware is exceedingly cheap, I just opted to replace both of the large bushing retaining washers as well as the bushings themselves.

So, here is the replacement of the hardware onto the new strut, starting with the bottom retaining washer and a new bottom rubber bushing. Here's the process, and a view of the installed hardware for the bottom portion of the bushings.
IMG_7120.jpg IMG_7122.JPG

From there, carefully raise the new strut up through the hole in the rear trailing arm, and up through the middle of the rear coil spring. CAREFULLY align the rear strut so that the hydraulic connection is facing toward the FRONT of the vehicle, so that you can easily reconnect the hydraulic banjo line to it.
IMG_7123.jpg IMG_7124.jpg IMG_7125.jpg

Here is a comparison of the old and new top and then bottom rubber bushings. As you can see, the bottom bushings take the brunt of the weight and shock, and thus are much more deformed than the top bushings are.
IMG_7130.JPG IMG_7131.JPG IMG_7117.JPG IMG_7118.JPG IMG_7119.JPG

After you get the strut inserted up and aligned, then take your 17mm bolts and thread them back through the holes in the bottom of the strut and up into the threaded holes in the rear trailing arm. It might take a little doing to get everything aligned, and tire your arm and hands out for a few minutes, but be persistent and it will eventually line up and go together. Once you thread the bolts in, then torque them down to the specified 65 Nm.

The next thing is to use your fingers to "pull" (extend) the top of the strut up through the hole in the body of the car behind the seat. Then you will want to install the top rubber bushing, then the top retaining washer, then the spring washer, and then the top nut. You don't need to cinch everything down at this point -- just assemble it for now so that the strut tube doesn't disappear back downward into the body of the strut.
IMG_7128.jpg IMG_7132.JPG IMG_7133.JPG IMG_7134.JPG

After that, put the wheel back on the car, and insert the lug bolts. Carefully lower the car onto the wheel, and tighten the lug bolts with the lug wrench. Then, going back inside the car, tighten the top nut of the strut with your 17mm open-end wrench and crescent-wrench counter-hold, to a torque of ~35 Nm.
IMG_7145.JPG IMG_7146.JPG

And the last step is to reconnect the banjo connector to the hydraulic connection on the outside of the strut. First, remove the red plastic protective cap, and set it aside. Insert the first of your two copper washers onto the connection, and then move the banjo connector into place. Then add your second copper washer, and then the nut that caps everything off. Tighten the nut to the MB specified torque of 25 Nm. The entire process is illustrated below.
IMG_7126.jpg IMG_7136.JPG IMG_7137.JPG IMG_7138.JPG IMG_7139.JPG IMG_7140.JPG IMG_7141.JPG IMG_7142.JPG IMG_7143.jpg

Here's what the properly connected and tightened banjo connector looks like with the new copper washers.

And here's what both items look like, all installed and tightened.

Replace both plastic caps by pressing them into place.

Rinse and repeat this exact job for the other side of the car. The second go-round should be considerably faster, because you now know what you are doing.

From there, you need to re-add the hydraulic fluid that drained into the pan. If it's relatively clear, you can re-use it by pouring it into the tank with a small funnel. I strained mine through a rag to remove any particles or dirt it may have picked up in the pan from being underneath the vehicle. I also spilled some hydraulic fluid in the process, so I ended up adding about one-half liter after the fact to bring the level back up to the proper place in the hydraulic tank under the hood.

After doing all this, you need to test and pressurize the system. Start and then rev the car up to around 3,000 RPM for about 2-3 minutes. You may want to warm the car up a bit before revving it, but you get the picture. If there are no hydraulic leaks at either strut, nor from the self-leveling valve in the rear, then you are done with the job.

"While I was in there" I decided to grease the Zerk fittings on my Feind Motorsports rear sway bar urethane bushings, because they were starting to squeak after two years being installed. I pulled out my grease gun and RedLine chassis grease, and gave them a shot of grease until it emerged around the bar, as shown in the photo below (the red blob of grease). Of course, most of you won't need to do this, but I thought I'd show this in case anyone ever needs to do it.
IMG_7148.JPG IMG_7149.jpg IMG_7150.jpg IMG_7151.jpg

I hope this process helps someone down the line with their 560SEC or 560SEL in replacing the rear hydraulic rams.



Site Honcho
Staff member
Sorry for the delay in getting the remainder of this job posted, guys. It was a long week and I didn't have much time to get to it.



Site Honcho
Staff member
For reference, the MB part numbers for the retaining washers and spring washers are as follows:

Bottom washer: MB # 116 326 00 67 ($14.50 each list; two required)

Top washer: MB # 202 326 00 76 ($2.40 each list; two required)

Spring washer: MB # 000137 010201 ($1.00 each list; two required)


E500E Guru
great write up as always. I remember dropping the struts in the yard with the car up in the air and no tension on the trailing arm. What is the pn for the 4 copper crush washers? grassyazz on the p/n!
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E500E Newbie
Gerry i just bought a late Gen2 Euro 560SEL the has Hydro suspension front and rear including the mercury filled sensors that detect body roll into corners and firms up the struts accordingly and has the hunker down option that lowers the car into stealth mode at speeds above 130kmh for James Bond style driving. All fully operational. It is the Euro 300hp version with 2.65LSD and fully loaded with orpho seats, etc etc.
Still to collect it. Interesting to compare that ride to the 560SEC SLS and getting my head around its associated added complexities in servicing those struts.


Just did this job to my pristine 1-owner 86 SEC parts car (yeah, I know, sacrilege...). One item - the red protective caps on the new hydraulic ram fittings (as seen in the pics above from Gerry) - once removed, there are very small rubber o-rings that were there to seal the protective caps. These o-rings should be removed before installing the copper seal washers. In the pic above when Gerry is removing the red protective cap, you can zoom in on the pic and see the o-ring still there; and then again the pic where Gerry shows the assembled banjo fitting - if you zoom in you can see the smashed o-ring protruding from the bottom copper seal. I doubt these cause hydraulic fluid leaks, but a housekeeping note.


View attachment 44234 View attachment 44240


E500E Newbie
I am about to do this job on my white coupe as i am swapping in a pair of rear Eibach lowering springs and a 19mm sway bar from Dkubus.
Of note i have the correct spring compressor kit which i will use in this job -(but have heard of guys not even using them with rear springs but instead dropping the trailing arms via a 2nd jack method?)
I have a K-mac rear camber kit but will see how this goes before tacking that task later.


Site Honcho
Staff member
Spring compressor is not REQUIRED for the rear springs on the 126 or the 124, but for safety reasons (and if one has a proper spring compressor to do the job) I'd always opt with using it.


E500E Newbie
I just removed everything today and i did use my spring compressor (the correct MB internal type with plates) which made getting the springs out very easy.
My right dust boot was split so i will swap another one of my spare hydro struts in.
My lower strut mount rubber bush was compressed as expected and as per your pics above Gerry
Will do the re-install tomorrow


E500E Newbie
Re-install completed and very happy with the ride now.
One suggestion i will make is even fitting the Eibach lowering springs i still needed the spring compressor to get them in.
Another suggestion i would add is -
when re-fitting the hydro struts and you have them in with the shaft just poking through the chassis hole it makes the job so much easier if you use another jack to raise the trailing arm up so the spring is compressed and then the top of the strut will come up easily into the fully seated into position making fitting the top rubber bush and steel washer etc a breeze
I could not fit everything into place without raising the trailing arm as the strut would not extend up enough into its proper seated position

In my case i also fitted the new 19mm anti-dive sway bar and that needed the centre pivot arm bracket modified including the U clamp to enable it to mount to the thicker 19mm bar ( i did not machine a notch in the bar as i did not want to do that (easier to modify the bracket)
I will let the springs settle down for a few days driving before i re-set the rear SLS which is a a simple procedure.
All fresh MB15 hydro fluid in the system now which is the ideal time to replace the fluid.


Active member
EPC for my 1991 560SEC against my VIN indicates rear SLS struts are 126 320 46 13

In the first post above Gerry lists this as 126 320 48 13

Any idea what the difference is?

EDIT: i see in the photo above from Gerry, his original struts were also 126 320 46 13
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Site Honcho
Staff member
EPC for my 1991 560SEC against my VIN indicates rear SLS struts are 126 320 46 13

In the first post above Gerry lists this as 126 320 48 13

Any idea what the difference is?

EDIT: i see in the photo above from Gerry, his original struts were also 126 320 46 13
The EPC spec's 126 320 46 13 as the correct strut from model year 1988 onward.

It specifies 126 320 48 13 as the appropriate hydro-leg for SECs with VIN ending in 428209 and later.

It looks to me like the two part numbers are interchangeable. HOWEVER, the 48 13 part number is specifically for "Euro" models, while the 48 13 part number has a notation for US and Japan models.

Both are available from MB and at the same price in Europe, further evidence to me that they are equivalent. The 48 13 unit is ~$50 more expensive than the 46 13 via the normal US discounters.

For earlier SECs, up to VIN 428208 and end of model year 1987, the hydro-leg part number 116 320 45 13 is specified.



Active member
Thanks guys!

One more tip for future users of this How-To. The copper seal ring crush washers for the strut banjo fittings are qty 4 of 007603012102


E500E Guru
I checked prices from Rock auto to partsgeek to ebay and MB Naperville is the best price still! at 301 for the pair!


Active member
Pro tip having just completed this job. You don't need to remove the wheels. And don't forget to order extra copper washers when you transfer the fittings over to the new spheres.


Site Honcho
Staff member
If you’re on a lift, especially, you don’t need to remove the wheels. Same with accumulator replacement.

However it’s not a bad step to take so that you can visually examine things in the area such as rubber boots, brakes/lines, bushings and so forth.


E500E Newbie
I have found you can repair the shock boots using the RS1952 made by Rancho in black. Slight modifications needed. On the small end, cutting a slit on each side to get it over the fitting and the ridges off the interior lip so it seats properly in the space available. Then secured with a zip tie. The other end needs 3 segments cut off and you will even get coverage of the rubber on the ball joint. I found it on Amazon as an "add on" item for $7.85 each shipping free shipping w/ prime.