Y'all may remember that a couple of weeks ago I was posting about my Euro 500SEL with the 6.9-style four-wheel hydro suspension, which was first pressurizing (lifting the car) at one end but not the other, then (after sitting overnight) seemed to be pressurizing properly, but still didn't respond correctly to manual manipulation of the level control valves (which ought to cause the appropriate end of the car to rise or fall quickly).
Well, I had another high-pressure leak, this one at one of the brake-fitting-type connections to the pressure regulator on top of the hydraulic fluid reservoir. It was just a little loose, but enough to make the front end drop to the ground. Since the system was already depressurized, I decided to follow a suggestion I read on the MBCA forums. Someone mentioned there that there's a metering system and filter built into the regulator, accessible by loosening what appears to be a large bolt on the rear of the regulator, which can sometimes cause trouble. I undid that bolt head and found an interesting mechanism: a long bolt with an o-ring halfway down it, an orifice in the form of a hole drilled crossways through the bolt, and a weird gold-colored object, which I guess is a kind of filter. It looks sort of like fine bronze wool compressed tightly into a conical shape; it's hard, but looks spongy and porous under a magnifying glass. It didn't seem dirty, but I soaked it in brake cleaner anyway while I cleaned out the orifice in the special bolt (dirty but not completely obstructed) and replaced the O-ring (hard and brittle). When I put everything back together and started the car, the front end didn't rise at all, but the rear end immediately rose to maximum height and stayed there. When I pressed down on the trunk, it wouldn't budge, as if the struts were stuck in maximum-pressure mode and the spheres weren't working. Baffled, I carefully reread the parts of the FSM dealing with the hydraulic system, and found a very brief and very vague mention that the leveling valves may under certain circumstances achieve maximum pressure and fail to release. The fix is to empty the system of fluid at the end of the car that's too high, make sure the level control valve is hooked up to the sway bar properly, and then start the car again and let the system repressurize correctly. That worked to bring the rear end down, but the front of the car was still too low. I took it out for a short, slow test drive, gingerly avoiding potholes and high spots in the road so as not to scrape the front end. It rode smoothly, as it's supposed to, and after about ten minutes the body leveled out. I stopped and checked the hydraulic fluid level---it was right in the middle between the high and low marks. But the car, though at the same height front and back, won't rise to normal ride height overall. It's too low all the way around, by about three inches; the suspension warning light is on; and manipulating the level control valves doesn't raise either end. Attached are some crummy cell-phone pictures of the metering bolt and the weird bronze filter thingy (as well as my shop helper, who finds the intake system of a warm M117 engine to be a perfect place to sit and meditate). I cannot find any reference to this mechanism in the 126 CD-ROM FSM, the 116 FSM, or the factory supplement for 1980 that covers the differences between the 6.9 and lesser 116s. I wonder if these parts are present in some form in the rear-only SLS systems, and, if so, might explain some mystery problems that people have had with their wagons? The big question at this point is, why doesn't the car pump up the struts to the correct pressure to reach normal ride height? I plan to test the hydraulic pump pressure next, but there seems to be conflicting information online as to whether a failing pump can actually even be a cause of low ride height. The Star Motors troubleshooting guide at http://www.starmotorsny.com/pdf/HydroSuspGuide.pdf refers to the fluid tank as a "pressure reservoir" and gives "lack of sufficient pressure in reservoir" as the first thing to check if the car is low all the way around and the warning light is on (but doesn't even mention the pump as a possible cause of those symptoms!). I find it hard to believe that the hydraulic fluid tank is really a pressure reservoir in the same sense as, say, the coolant overflow tank. For one thing, if I open the filler/dipstick cover on top while the car's running, there's no sense of pressure being relieved (like there is with the cooling system); for another, the dipstick cover itself is not designed to seal tightly (it doesn't screw in, just a press fit). (But if it really is subject to pressure, I need to take it out and check it for leaks, I guess.) There also seems to be some disagreement as to whether the system constantly recirculates fluid---in which case the health of the pump would be extremely important---or whether the pump is only used when the load at the front or rear of the car changes significantly, to add fluid to that end if necessary, and the rest of the time each set of struts and spheres becomes a closed system---in which case the pressure of which the pump is capable would be less important (it would just mean the car would respond slower to changes in cargo load). Any suggestions appreciated! Alex -------------- next part -------------- A non-text attachment was scrubbed... Name: IMG00232-20110104-1854.jpg Type: image/jpeg Size: 213649 bytes Desc: not available URL: <http://okiebenz.com/pipermail/mercedes_okiebenz.com/attachments/20110106/2e5a7dd5/attachment.jpg> -------------- next part -------------- A non-text attachment was scrubbed... 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