W126 Self Leveling rear suspension low ride height

Ever since I owned my 560SEC, it has always ridden too low in the rear.   I have attempted to adjust it a couple of times, but was never able to get the correct height.   Using the factory procedure to set the neutral height did not work.

At this point a lot of workshops would suggest to rip out the system.   This is a really bad idea.   The self-leveling rear suspension is a simple system that works really well.   Most problems can be simply fixed and are generally cheaper than ripping out the system.   Factory SLS cars never ride properly once the system is removed as the rear springs are always wrong.   The SLS springs are very soft and not suitable for regular shocks.   The replacement springs most use are too hard and cause the cars to ride badly.   The factory was very careful to select the right springs for each car based on the options selected.   For example, a car with a sunroof might have different rear springs than one without.   There is a system of points you add up that determines which springs and spring pads should be used.

As I wasn’t able to fix the system with the normal adjustments, I took the car to my mechanic who is very experienced with it.   Initial tests showed poor fluid flow to the valve, and then even worse flow to the struts.    Based on that I ordered a rebuild kit for the pump from Mercedes Source and a brand new valve.   The post 1986 cars use a smaller valve that I do not believe is rebuildable.   The earlier square valve is.     It looked like the pump was not making enough pressure, and the valve worn internally.   Changing these should fix my W126 Self Leveling rear suspension low ride height.

This valve originally had a W124 part number.   Later, it was superseded to a W202 part number (A202 320 02 58).   Funnily enough, when I got the valve, it had the 202 part number on the box but the W124 part on the valve itself.   The valve wasn’t cheap, but it is still available.   In some ways I’m glad to be replacing it while it is.   I suspect this part will go NLA in the next couple of years.

Fitting these parts meant there was now good flow of fluid to the rear of the car, but not to the struts/spheres.    The new rebuilt pump also showed up a small leak in the high pressure hose that was sent away to be rebuilt.

Checking the lines carefully highlighted the final problem – and it was the work of a previous owner or mechanic.    At some point the hydraulic lines had be cut near the subframe.   They had been joined together, but the two lines reversed.   I’m not sure why these lines would have been cut.  Perhaps the subframe was removed at some point.   In any case, with the supply and return lines reversed, the system never worked very well.  Its surprising it worked as well as it did.

With the lines now properly configured, the ride height is set correctly and the car rides much better than before.   My W126 Self Leveling rear suspension low ride height problem is solved and the SLS should be good for years to come, other than the normal sphere replacement.