'84 300TD Rear Level Control - PeachParts Mercedes-Benz Forum

dsmess · #1 09-24-2003, 12:10 PM

Hello All,

I used to feel the rear of the car lift up at startup, and sometimes added fluid because of a small leak in one of the shocks. Now the level stays the same..and I sense no movement. Perhaps it never or rarely pumps?

Recently, I had a couple hundred pounds in the back and the rear was obviously too low. I put the rear tires on ramps and noticed the control lever could be moved (with resistance) even without removing the link from the sway bar (perhaps a problem there). The rear pumps up and down, but the lever must be moved over an inch in either direction to get the movement.
In order to maintain the level it has to be more sensitive that that!

I looks like I need to dig into this...study the manuals..perhaps check the system pressure. I'd appreciate hearing suggestions.
Anybody had similar symptoms?

R Leo · #2 09-24-2003, 12:57 PM

Marlene does this same thing sometimes...

If she looks like she's squatting I walk back, hop on the bumper and work the suspension a little. She'll pump right up.

My theory is this: after a zillion miles of the level sensing valve arm pretty much sitting in the same place, the valve's actuating arm resists moving outside of its normal range of travel. When the suspension is pushed down with a load, it simply deflects the transverse rod in the suspension instead of moving the valve arm and correctly sensing the ride height.

Someday, I'll get around to changing out the fluid. At that time I may pull that valve apart and see if there is anything obviously wrong and if cleaning helps any.

As the accumulators age, the suspension will settle too. Recently, I've had to adjust the height of the rear end.

I have the height spec at home...I'll post it here when I can.

dsmess · #3 09-24-2003, 07:02 PM

After disconnecting the linkage I don't notice much of a detent.
I tried sitting a couple people on the rear bumper. The rear dropped maybe an inch without pumping up. It looks like there is not enough control arm movement to create the pumping action.
I'm thinking the pump may be weak.

You may have the same problem. In the past I did rock it up and down and get it to lift some.

Thanks,

R Leo · #4 09-24-2003, 09:00 PM

I'm pretty sure that my SLS/hydropneumatic suspension pump is working OK. When I was under there adjusting the level, I moved the actuator arm while the engine was idling (600-750 rpm). The car moved both up and down rather briskly.

Those are simple radial piston pumps that are lubricated by the engine and hydraulic fluid. 'Wearing out' is possible if the system was run completely out of fluid or if the fluid is contaminated and has damaged the pump.

Another cause of slow lifts may be a clogged actuating valve or pinched/damaged hydraulic supply line that isn't admitting enough fluid to the cylinders.

Do you have the FSM for the 123 chassis? If not, let me know and I'll scan the appropriate pages for you.

dsmess · #5 09-25-2003, 11:34 AM

OK, the question is: How much moverment of the lever was needed to start the rear lifting? In my case it is at least 1 to 2" at the lever end. I'm going to check my 'transverse rod' connections near the wheels...they may be loose.

I have the manuals.

Thanks,

#6 09-25-2003, 12:06 PM

I can move my lever about 1/2" to start raising and 3/4" to start lowering. Also, when I revv my engine from idle to 2500rpm+ in neutral/park it will raise another 2 inches.

McRoth · #7 09-25-2003, 12:20 PM

I've got a Euro 240D with this same system on it. I've got the same types of problems with it too. If I want to rebuild the valve, where do you get the kit? I'm guessing it's a stealer only item? Do the accumulators go bad very often? Just checked fastlane & they're not exactly cheap!

Thanks!

#8 09-25-2003, 12:23 PM

A 240D with a hydropnumatic level control? Add that to my list of new MB knowledge.

McRoth · #9 09-25-2003, 12:26 PM

Yep, kinda weird! I've only heard of maybe one other one on this board, but I don't remember who it was right off.

lrg · #10 09-25-2003, 01:50 PM

The accumulators are basically half nitrogen and half hyd. fluid separated by a rubber bladder. When they fail it's usually because the bladder ruptures and the whole sphere fills with fluid. This is generally noticable as a very hard and poorly dampened rear suspension but may not be particularly obvious if just one sphere/accumulator is shot. The system should still move the rear up and down pretty normally, even with two bad spheres. Unless the car is riding hard the spheres are probably OK. Before you rebuild the valve:

1.) as suggested, check the drop links at each wheel to be sure there isn't any play. They are pretty easy to replace but a dealer supplied part.
2.) if the fluid in your system is more than a few years old it's probably time to give the system a good flush. There is a bleed nipple on the valve but to be thorough it's a good idea to remove and drain the accumulators too. (plan on making a bit of a mess). Don't forget to replace the filter in the resevoir (yes, there's a filter in there).

There should be some play in the valve before it opens because the system is designed to allow for normal suspension movement without the valve constantly operating. If everything else checks out it may be a simple adjustment issue.

I've never rebuilt the valve but understand it's not too bad a job. The dealer should be able to get you a rebuild kit. I STRONGLY recommed you use flare whenches on the hyd. line connections as these are notoriously easy to strip. In general though, the SLS is pretty trouble free so if it ain't broke, don't fix it.