Re: 1988 635csi electric self leveling (archive)

If you ever need to add fluid to the SLS, then you should look carefully for a leaking shock absorber, which you will most likely find. The second most likely source for this loss is a broken bladder inside of one of the 2 'bombs'. Here is an article I saved on troubleshooting the SLS which may help you, The answer to your question is near its end. Note that your costs may vary, this is from years ago:

Rear Suspension -- Self Leveling - Don Schmidek

The '88 & '89 sixes have self leveling suspensions. The suspension consist of special shocks, hydraulic accumulators in the wheel arches, a pump and control system under the spare tire. There are also linkages connected to the rear torsion bars, etc. which sense the height of the car, plus piping, hoses, etc.

If your car rides very harshly or the height level keeps on changing, i.e. you hear the pump cycling frequently, the chances are that your accumulators are shot.

The good book states that the life of these may be as short a s 50,000 Km. Typically it is probably about 100,000 miles. You can check out this problem by rocking the rear of the car -- push down on the rear bumper hard. If you get very little motion, you may have the
problem.

You can also check by bleeding the accumulators --- see below -- by disconnecting the big hose connection and seeing how much fluid runs out. If you get about 200-400cc from each accumulator, that suggests that they are defective. If both old accumulators were completely full of fluid, it indicates that the Nitrogen pressure charge had been lost. This may be due to the bladder breaking or the Ni just leaking out.

To replace these, jack up the rear by the differential (use supports on the two sides via jack stands). Turn on the ignition (do not start the engine) to allow the system to normalize and depressurize -- for about 1 min. After that, just remove the two pipe connections to each accumulator (be sure to cover them, not to let dirt into the pipes) and let the fluid bleed off into a pan. Remove the old accumulators (3 nuts) and install new ones. Be careful not to miss-thread the fittings. Add fluid to the tank -- if you remove all the fluid before you start the process you will in fact rejuvenate the fluid -- all it takes is about 1 liter -- and you are ready to roll. Do not have to bleed the system -- but after you let the car off the stands, turn on the ignition and see if your car adjusts. Sit on the trunk edge, and see if it self adjusts. You can also measure the height from the ground to the bottom of the rear wheel arch -- it should measure about 27 inches. Finally, you should now get a little bouncing motion if you push down on the rear bumper.

Once done, you will find that your 6 rides comfortably over road irregularities as it was meant to, corners 200% better and no longer skitters in turns. Now for the costs: Accumulator run about $130 each --- plus $10 shipping -- total $270. You may get quotes up to $270 each, but keep on shopping. Note that the retailers pay the wholesaler just $85 for each -- so there is plenty room to bargain.

You should use Pentosin 7.1 CHF as called out for hydraulic fluid -- costs is about $16 per liter. It is available in foreign car shops.
Happy driving.

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