The SLS valves for W115/123/126/124/201 etc rear axles are totally different from the valves on the 6.9 and W126 with four-wheel hydropneumatic suspension.
The rear-axle-only SLS version has a base pressure ball valve which is designed to guarantee a static pressure irrespective of the position of the control lever. There's never "no pressure" in the suspension circuit (unless the base pressure valve spring is weak), and the steel suspension ensures that even a leaky valve won't result in any dramatic height changes when the car is off. MB sells a rebuild kit 000-586-00-32 (about $100) for these valves. The four-wheel levelling system on the 6.9/W126 is totally different from other MB SLS systems. It is a shameless (probably licensed) copy of the Citroën system. The height control valve is actually much simpler than the rear-SLS valves (fewer components), but it is made to MUCH tighter tolerances. The system, including cutaways of the height corrector valves, is described here: http://www.citroen-ds-id.com/index.html?hc/chapter4.html Another useful link: http://www.citroenet.org.uk/miscellaneous/hydraulics/hydraulics-1.html The machining tolerances on these valves are tighter than on the SLS valves, because any leakage in the valve will cause the car to sink to the ground when shut off. There are no springs to back up the hydraulic pressure. This requires extremely tight valving, and a conventional machine shop would not reliably be able to achieve those tolerances, certainly not at a price you'd be willing to pay. Of course, leakdown could also be caused by any other component in the pressure circuit, which is why people often replace the levelling valves only to discover that wasn't the problem. Unless the corrector valve is leaking externally or seized, it's generally fine. Below, extracts from http://www.citroen-ds-id.com/gen/Asnieres.html describing the process of making the slide valves in the height correctors. I wouldn't be surprised if MB sourced their valves from Citroen, rather than bothering to set up another OEM... >The finishing processes are carried out on centerless grinding machines, and >vary according to the profile and dimensions of the slide valves. On each >pass, >the machining chip gets smaller and smaller, down from 0.06 mm to 0.04 mm to >0.01 mm. At this stage the part is ready for superfinishing. There are still 5 >microns left to be removed before the setting is perfect. This is done by >lapping, and the chip now is no more than micron dust. Lapping is performed on >the circular plate of the lapping machine, a form of grinding wheel, on which >the operator sets out 150 slide valves into the recesses provided for that >purpose, a second rotating plate rolls and polishes the slide valves in their >axis rather like ball bearings. The operator, guided by his know-how and the >sixth sense born of experience, carries out the inspections he deems necessary >as the setting approaches its final development. He also turns the slide >valves >over in order to correct for the conical effect produced by the lapping >process. > >Three levels of tolerance compliance have to be attained by the slide valves: >1 >micron in diameter, 0.5 microns out-of-shape, and 0.3 microns in surface >finish. In order to observe the micron and even lower requirements, inspection >to within a tenth of a micron by the measuring apparatus is required. Of >course, not only does the measurement have to be precise, but it must also be >reliable under workshop conditions. To obtain this, a number of precautions >(e.g. avoiding continual variations in temperature) have to be taken. The >solution adopted at Asnières is simple and foolproof: the operator compares the >part with a benchmark of the same dimension and material, which is regularly >checked by the metrology laboratory of the Quality control department. > Alex Chamberlain wrote: > >There are several leveling valves on eBay from 123 wagons and 560SELs, >but starting price on each is $100 or more, which is a little more >than I want to spend just for research purposes. I wish I knew what >the difference is between those and the kind at the rear end of a 6.9 >(which is also on my 126). > >I would take apart the one on my car, but it's working fine, and I am >not confident enough in my ability to put it back together right. A >cheap junkyard one, though, that's another story. Considering that >the 123/560SEL part goes for $300 or so new, and the NLA 6.9 part goes >for $1K or so used, it seems to me somebody could make money >rebuilding these---or even, in the case of the 6.9 part, manufacturing >a drop-in replacement from scratch (a la the Unwired Tools replacement >116 ACC brain). How complicated can it be inside? A few fluid >passages, some holes tapped appropriately for the lines, and a valve >that changes flow rate depending on the position of a lever? Sounds >like something any undergraduate mechanical-engineering student could >design and any machinist could build. > >Alex -- David Bruckmann, Palo Alto, CA Current Reality: 1970 Mercedes-Benz 220/8 (200,000 km) "Blanche" 1972 Mercedes-Benz 280SEL 4.5 (160,000 km) "Blauer Engel" 1973 Mercedes-Benz 450SLC (200,000 km) "Lottie" 1976 Citroen 2CV6 (145,000 km) "Piaf" http://dolly.bruckmann.com/ 1976 Mercedes-Benz 300D/8 (200,000 km) "Willow" 1979 Mercedes-Benz 300D (425,000 km) "Brown Betty" Shady Past: 1970 Citroen DS21 Pallas (170,000 km) "Goettin" 1971 Citroen DS21 Pallas (137,000 km), 1972 Citroen DS21 Pallas (502,000 km) 1978 Mercedes-Benz 300D (1,200,000 km or thereabouts) "Sieglinde" 1979 Mercedes-Benz 300TD non-turbo (260,000 km) "Diva" 1981 Citroen 2CV6 Charleston (120,00 0km), 1988 Merkur XR4Ti (209,000 km) 1981 Peugeot 505 GRD (350,000km), 1984 MB 300TD (385,000 km) "Gertraud" 1985 Toyota Camry "The Slamry" (330,000 km) 1986 Renault 9 1.7L (155,000 km) 2002 VW Golf GLS TDI "The Hated Golf" (74,000 km) ---------------------------------------------------------------------- _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
