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.
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.
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)
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.
After that, remove the lug bolts the rest of the way and remove the wheel from the vehicle.
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.
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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.
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.
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Here are images of the compartments, with the caps removed. Note the hydraulic line attached to the top of the strut.
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.
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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.
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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.
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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.
CONTINUED IN NEXT POST.