DIY: Rebuild the self leveling suspension SLS valve on w123 300TD wagon sagging rear
 

First let me apologize for the overly long thread title. I wanted to make it amenable to searching the archives.

This post is meant purely as a DIY. Time to give back to the forum.

The car: 1984 euro 300TD turbo, but I think this will apply to most w123 wagons with self leveling suspension (SLS).

Problem: The car rides fine, not too bouncy or bone jarringly stiff *. When the engine is running the car sits level, but after being parked for a few hours the rear end of the wagon sags down a bit. Its most noticeable because in the morning when the car is started you can feel the back end up the car raise up. The SLS valve (figure 1) is wet with hydraulic oil. The SLS actuators (rear struts) are NOT leaking (they are dry).

Causes: 1) One or more of the o-rings in the SLS valve is leaking and 2) the rear coil springs are either worn or broken and should be replaced (or possibly shimmed if it doesn't sag too much), and/or 3) the SLS ride height is adjusted too high. In my case all three are true, but if you can feel your car raise up when it is started at least two of the above are true (unless you just loaded it down with about 400 lbs). If the car has good springs, the unloaded car won't sag even if the SLS is disconnected.

Fix: 1) Rebuild (replace the o-rings in) the SLS valve. 2) Replace the rear springs (beyond the scope of this thread). 3) Adjust the ride height.

Rebuilding the SLS valve:

Tools required: jack and (2) jack stands or (2) ramps, (2) 17 mm wrenches, 12 mm open end wrench, 11 mm open end wrench, (2) 10 mm wrenches (one open end), 8 mm allen key, a small bent pick (dental pick) or very sharp forceps) 1 foot piece of 1/4" ID hose, clean dry plastic bottle, drain pan.

Parts Required: metric o-rings (buna-nitrile or viton) dimensions are listed in mm as cross section (CS) x internal diameter (ID)
(1) 2 x 58, (2) 2 x 7, (1) 1.6 x 10.1 , (1) 1.6 x 7.1 (** see below for availability), 1 liter of MB hydraulic oil (to replace lost fluid, available through Fastlane) the total capacity of the SLS system is 3.5 liters.

Time required: 2-3 hrs

Difficulty: No more difficult than adjusting the valves

1) Chock the front wheels securely and jack up the back end of the car just enough to get under it. Place jack stands under the trailing arms and carefully lower the car. Make sure that the car is secure before you climb under it. Alternatively, back it up onto ramps, then chock the front wheels. The idea here is that the rear suspension should be compressed before you open the hydraulic system and release the pressure, this will minimize the amount of hydraulic fluid lost. (If your springs aren't too bad and you don't eat too much you may be able to do the entire job without jacking up the car.) Ideally, the suspension should be compressed and the car should be sitting level (If you had good springs you could do this).

2) Disconnect the SLS height adjusting rod (figure 1.A, looks like a throttle linkage rod) from the valve lever arm (figure 1.B). Use the open end 10 mm wrench to hold the ball stud and another 10 mm wrench to undo the nut. (The picture for figure 1 was taken with the car jacked up and the wheels hanging, that is why the lever arm is pointing down from "normal".)

http://www.ultimatekayakfishing.com/..._57_238341.jpg

3) Start the car and crawl back under it. VERY CAREFULLY release the pressure on the SLS actuators by rotating the SLS valve lever clockwise (CW) about 10 degrees. WARNING: The rear end of the car will come down to its lowest point (resting on the springs), and if your springs are really bad it may squish you. My springs weren't too bad and I could do this with the car on the ground, so I had fun playing with the valve lever for a while (car goes up, car goes down, car goes up, car goes down, etc.). Don't let the car raise too far. I don't know that anything bad will happen, but it seems like a bad idea to overextend the actuators. Turn the car off.

4) Attach a hose to the bleeder valve on the SLS valve (figure 1.C) and put the other end in the bottle. Loosen the bleeder valve (11 mm ? open end wrench) to drain any residual pressure in the SLS system.

5) Place the drain pan under the valve. Disconnect the hydraulic oil feed and return lines from the valve (figure 1.D, 12 mm open end wrench). They may leak oil when loosened, but it should stop in a minute.

6) Disconnect the hydraulic lines to the actuators from the valve (figure 1.E), 11 mm open end wrench). They may leak oil when loosened, but it should stop in a minute.

7) Remove the two bolts holding the SLS valve to the bracket (figure 1.F, two 17 mm wrenches).

Part 2
 

Take the valve to a clean work area. Before you disassemble the valve, note the relative orientation of the two halves (honestly I don't think it matters, but hey better safe than sorry). My valve was marked 115- 328-0521. Also, when you separate the two halves of the valve there is a piston with two springs in it that may fly apart, so proceed cautiously.

8) Remove the two bolts holding the two halves of the valve together (figure 1.G, 8 mm allen key and 17 mm wrench). Beware of small flying parts. Note the orientation of the cam inside the valve (figure 2.A), the lobe of the cam points away from the valve lever arm (toward the hydraulic line fittings toward back of the car). Replace the 2 x 58 o-ring (figure 2.B). In figure 2 the o-ring is stuck to main valve body, it should be in the recessed channel on the other half (figure 2.C). This is probably the o-ring that was leaking, but since its out and apart you might as well replace the rest of the o-rings.

http://www.ultimatekayakfishing.com/..._57_198806.jpg

9) If it didn't come flying apart when you separated the valve, pull the cam off of the lever arm shaft. Carefully remove the piston (figure 2.D) without scratching it. I used a pair of needle nose pliers and some cotton cloth to prevent scratching the piston. The piston assembly is actually 2 pistons (outer and inner), 2 springs and a ball bearing (figure 3). There is a second larger ball bearing trapped in a passage in the valve body behind the piston. I didn't measure any of these parts so I can't help you order replacements, so don't lose them.

10) Remove the bolt holding the valve lever arm to the shaft (figure 1.H, 10 mm wrenches). Pull the valve lever arm off of the shaft. Push the shaft out through the valve body. Use the bent pick to remove and replace the two o-rings from the valve body (2 x 7) where they seal against the shaft. Re-install the shaft, lever arm and 10 mm bolt.

11) Use the bent pick to remove and replace the outer (1.6 x 10.1) and inner (1.6 x 7.1) o-rings on the outer piston. Reassemble the piston as follows (figure 3): i) drop the larger ball bearing into the passage in the valve body behind the piston letting it fall toward the center of the valve (not pictured), ii) slide the larger spring over the inner piston, iii) slide the inner piston (and spring) into the outer piston, iv) insert the smaller ball bearing into the inner piston from the bottom, v) insert the smaller spring into the inner piston from the bottom, vi) insert the piston assembly back into the valve body.

http://www.ultimatekayakfishing.com/...8_57_53613.jpg

12) Rotate the valve lever arm to its correct position (away from the hydraulic line fittings). There are corresponding holes on the lever arm and the valve body that line up when it is in the correct position. Re-install the cam on the lever arm shaft with the biggest lobe pointing away from the valve lever arm and the smaller lobes pointing toward the top of the valve (figure 2.A).

13) Reassemble the two halves of the valve in the original orientation. Re-install the two bolts that hold it together (figure 1.G). Note that one of these bolts is longer than the rest as the valve body is thicker in one corner.

14) Reinstall the valve on it bracket and reconnect the hydraulic lines.

15) Check the level of fluid in the hydraulic resevoir (I only lost about 250 mL), it doesn't need to be full just so long as it won't run the pump dry. Start the car. Play with the valve lever arm again (car goes up, car goes down, car goes up, car goes down, etc.). The car should raise when you turn the lever about 10 degrees CCW from horizontal and lower at about 10 degrees CW from horizontal). If it requires large rotation of the lever to raise and lower the car, you may have installed the cam in the wrong orientation.

16) Use the lever arm to adjust the ride height where you want it *** and return the lever arm to its "normal" position (when the hole in the arm and the hole in the valve body line up). If your car rode at the proper height before, you can just reconnect the adjusting arm (and order new rear springs). The PO had adjusted mine to ride too high. The adjusting rod can be lengthened (to make it ride lower) or shortened (to make it ride higher), by loosening the 10 mm locknuts on the center shaft at the sockets and the center shaft turning the center shaft by the 10 mm fitting in the middle. Retighten the lock nuts and you're done. (The picture for figure 1 was taken with the car jacked up and the wheels hanging, that is why the lever arm is pointing down from "normal".)

* Poor ride quality in the rear is often an indicator of bad accumulators.

** I was informed by FastLane that the original MB rebuild kit for this valve is no longer available. I purchased the small o-rings from McMaster-Carr and the large o-ring from Marco Rubber. Unfortunately, you cannot buy just one o-ring, so I ended up with enough to rebuild 20 valves. It cost me just over $75. If you need to rebuild your own valve, I'd be very happy to send you 2 complete sets of o-rings for $10 (shipped). I hope this isn't viewed as solicitation, I'm just trying to help out (and maybe break even). EDIT 01-03-08: I broke even and ran out of the large o-rings. Contact Andrew at "Biodiesel300TD" for o-ring kits.

** A word about proper ride height: The unloaded curb weight of the car should be carried entirely by the springs (i.e. If the car has good springs, the unloaded car won't sag even if the SLS is disconnected). I keep repeating this because its important. The fix I describe in this thread is only part of the job (the easy part), and if you don't replace the springs (or shim them) you will likely have to repeat the job all too soon (or worse, prematurely wear out the actuators). When the SLS system is working properly you should never know its there until you put a heavy load in the rear cargo area with the engine off. This is the only time you should see the car level itself on start up.

Someone recently posted a great blue print style mechanical drawing of a w123 sedan that shows measurements for the stock ride height (though there may be differences between euro and US specs), but I can't find the thread right now.

Big thanks to whunter, who suggested that when I do the repair I document it so I could write this DIY.

Very nice write up. Thanks.

Awesome write up, this is just what I needed. Ok..I had to edit since I see the kit that I just saw here the other day is indeed no longer available (part no. 000 586 00 32).

:beerchug: Cheers to Douglas.Sherida! Nice work.

It's an easy job, but you have to pay carefull attention to how this come apart or you'll never get them back together the right way, so it's good to have the good photos for help.

Very nice job Douglas!
Very nice.......:thumbsup:

Nice write up. Here's another tip. Replace the adjustment arm while your doing it. The adjustment arm has plastic inserts that keep the ball joints together, mine deteriorated and the arm came off while I was in a express lane in a construction zone. All of a sudden the back of the car went way up. I had to continue about three miles before I could pull over and manually adjust the lever. It over extended the system killing my new actuators.

Great write up.

Can you elaborate some more on the idea that the SLS carries no load with an empty wagon and that the springs alone should carry the load under these conditions. I've seen this posted before here but I read something somewhere that made me question it. I was left with the impression that the hydraulic struts were designed to carry some load even with an empty wagon.

If they didn't carry some load, then when a line breaks or similar event the back end wouldn't sag to the ground......

Great write up, Doug! Bookmarked for future reference.

I'm suprised this hasn't been made sticky yet. Very extensive WU. Great job!

Excellent! Now I REALLY want a wagon.

I'm not sure how to elaborate any more than I have.

I stress the point mostly for owners of wagons that sag badly (> 5 cm). Rebuilding the valve as I've described will completely alleviate the symptom, but it does not really fix the whole problem.

I cannot prove the assertion, but I'm convinced that the SLS should carry near zero weight in the unloaded car (maybe the difference between an emtpy vs full tank of fuel, ~ 100-125 lbs). The only true test I can think of is to release all the pressure from the SLS (open the bleeder) on an unloaded car with a new set of rear coil springs. I haven't done that yet, but here is the data I do have.

On my 84, the 23 year old springs allow the rear to sag about 4 cm. (It was about 7 cm originally because of the PO's overzealous height adjustment.)

On my 85, the sag is less than 2 cm.

Both cars have 170K on them. The 84 was a registered school bus (yes, I call it the "short bus"), so it was always carried the extra weight of passengers. The 84 will be getting new springs, the 85 will be getting sold. ;)

When you open up the bleeder valve, or undo a hydraulic line, the back end of the car drops. That is why it better be up on ramps, and why we always give that warning.
Same with the W116's with SLS. They drop to the ground when the system is compromised........

Jimmy,

I can't speak to the w116 SLS, since I don't know.

But you make my point exactly.

The low point to which the (unloaded) car drops when the SLS system is opened is a measure of the "quality" of the rear coil springs. The bigger the drop, the worse the springs.

Ideally, it shouldn't drop at all.

But, unless I KNEW it wouldn't drop I wouldn't open the SLS system without ramps (or jackstands).

I now have the w123 SLS O-Ring kits available. If you are intersted in a kit please email me or send me a PM. I'm offering one kit for $10, each additional kit is $5. This includes all the o-rings in the w123 valve, shipping, and a PDF copy of sealing instructions.

Wonderfull Post

Spings carry the weight....
 

To answer the question, the springs are meant to carry the load (support the vehicle weight) with the engine and leveling system off. If the car sags when cold the springs need to be replaced. The leveling system is meant to "augment" the springs under load. If you need (or want) a little more beefy suspension, or if you go to normal shocks you will want to use (HD) springs for a 300SD as they are a bit more heavy duty.

It is too bad Mercedes does not carry the rebuild kit any more. I just bought mine 4 months ago from the local dealer (RAB Motors:AKA Robbers and Bandits) for @ $80.00. It comes with replacement springs, pistons, ball bearings and copper washers besides the main o ring. One might try a dealer to see if they have any in the back room.

I just realized this was stated at the beginning.

Self Leveling Valve
 

I know this is an old post but I thought I'd try. I need to rebuild my SLS in my '83 TD. Do you still have these 0-rings?
Thanks,
Tyler
kumaaz@yahoo.com

I do still have the kits available, and I responded to your email, so information awaits you!:D

sls rebuild
 

I followed the direction real careful, but for some reason the small spring inside the inner piston keeps slipping out as I put the piston assembly on top of the larger ball (bearing). What am I to do?

Robert

I rebuilt a spare, installed it and it works fine. I now have my original rebuilt and ready to go if someone wants to buy it. There are some differences in these so make sure it's the one you need. Mine is from an '83 300TD. The number on the body is 115 328 0521 which is covered by the bracket but I have lots of pictures.

sl valve
 

do you still have the rebuilt valve, and if you do can you sell it to me?
Robert

I have everything done except for one of the orings mentioned above. I pulled one out of the valve body groove, and installed a new one. Where does that second one go???? My kit has 2, and you speak of 2 being replaced. Surely they can't both go in that one groove. :eek: I barely got the one in there, and there was only one in there to remove.
I'm dead in the water until I figure this out, but at least all other pieces are cleaned, rebuilt where required and ready to reassemble......

OK, I'm rebuilding a pump stamped 42 78, which I'm guessing is 42 week of 1978. Andrew was nice enough to send me a pic, and his Valve had two grooves for orings and was stamped 03 83, I guess the 3rd week of 1983.
This valve assy was from a '79 300TD, so there is apparently a change of the part somewhere.
I'm sure we can all guess why.....:(:(

I wonder if you have kits for the SLS cubes found in the 6.9's and the W126's with full SLS.

I had the same experience rebuilding a 82 300TD valve. Only one o-ring where the directions show two.

Hey Al. I got my kits from Andrew, Biodiesel300TD [see post 16]
I don't know a thing about 6.9's.......:(

These kits are for the 123 valve. I also know nothing about the 126 SLS. I should start learning about them though. I do know that the 124 valves are a sealed unit and are not rebuildable. So I wouldn't be surprised if the 126 valve is the same way.

It looks like the early 123 valve only have 1 seal on for the shaft of the lever arm that goes through the body of the valve. I have a note in my instructions about that now. Luke do you happen to know the data stamped into your valve?

SLS Valve Schematic?Does anyone have one?
 

Just took my valve apart, it was wet and am awaiting the o-ring kit. I noticed that one of the brass fittings that attach to the valve body has a copper washer (small thread fitting) while the larger thread fitting did not have a copper sealing washer but appears to have a taper where the fitting meets the valve body. Anyone know if this requires a copper washer too? A schematic of this valve would be really helpful showing all parts for the SLS valve. Does anyone have one? Thanks!

Further SLS rear suspensino system questsion
 

This is from a previous post about the SLS system

To answer the question, the springs are meant to carry the load (support the vehicle weight) with the engine and leveling system off. If the car sags when cold the springs need to be replaced. The leveling system is meant to "augment" the springs under load. If you need (or want) a little more beefy suspension, or if you go to normal shocks you will want to use (HD) springs for a 300SD as they are a bit more heavy duty.

Is this true? Can the springs be adjusted by adjusting the height of the torsion bar if the top coils are visibly compressed?

All these questions! i love it.

-philip

If the thread part of the fitting is tapered then you don't need a crush washer.

The springs maintain the unloaded ride height. If your rear is low when unloaded and not settling over night and the SLS system is in working order and properly adjusted then your springs are probably tired. You can adjust the SLS system to lift the rear to proper hide height but you are going to have you SLS working overtime. It will always be holding the car up.

Larger ball bearing
 

After I dismantle the valve, there is a larger ball bearing that fell out from the valve.....where is this ball bearing suppose to be seated?

Please advise.

Thanks in advance.

NPK

Found it "drop the larger ball bearing into the passage in the valve body behind the piston letting it fall toward the center of the valve (not pictured)," Thanks.....

Mercedes FSM makes it very clear: the unladen weight of the W123 wagon with SLS rear end the rear weight is carried by BOTH the springs and the baseline pressure fed to the spring strut by the level control valve. This engages the shock absorbing effect of the system all the time. If your wagon rear is sagging under normal unladen conditions then replacing springs (or maybe shims only, they say springs) is THE solution. The SLS is designed to respond to loads to bring it back to level if it sags low due to weight in the rear.

this information is directly from MB FSM 32-501.

Fantastic write up...I may be doing this.
 

Question though: I just bought an 83 300TD with 199,xxx miles on it, and the oil in the SLS tank is as black as coal, really it looks like crankcase oil. Any ideas on why this would be? Just never been changed? Cross contaminated with crankcase oil somehow? Serviced with the wrong oil? The mysteries of a previously enjoyed car.

yes, when the pump o-rings wear out, engine oil soot does contaminate the sls system. also, as the rubber hose begins failing, it'll contaminate the oil. it's pretty simple to drain, and flush most of the fluid out, but I'd change the pressure and return hoses first.

So, should I replace the o rings in the pump? Is that even possible?

I would have to say that the first thing to do if the rear end sags in unladen conditions is to see if the baseline pressure is 435 to 550 lbs. If it isn't there may be another problem there somewhere. Also the complete rebuild kit for the w123 leveler complete with orings springs pistons and balls is now available at Mercedes. I got one from the local dealer not a month ago for about $50.

You can rebuild the pump seals in order to prevent engine oil from entering the pump. You can purchase the kits from Kent at MercSource, or go straight to the source though these guys in TN.

I bought the kit through them, but have yet to do it. I am going to do it by the end of the year, hopefully.

When I changed my accumulators, the oil was black from the engine oil mixing in. But, the reservoir's oil is clear. I checked, and the pump is recirculating to the reservoir while engine is running.

Anyone need control valve O rings?
 

Have a 280TE that am sorting. No fluid leaks, no bouncy or harsh ride, replaced the sway bar links, checked one accumulator just to be sure, flushed the fluid (golden yellow), seeing get a decent flow. However, still not getting the rear to rise up with load (easily 200 pounds (two boxes of heavy spares, a 75 pound Golden, and 45 pound Goberian (my helpers)).

Do have visably bad caster and inside edges of the newer tyres bald, which is one reason why replaced the sway bar links.

Ride height with no fuel in the tank on driver's side is 24 1/4" to the wheel well lip and 23 3/4" on the passenger side. I have searched and searched and no specifications.

Thinking to order the control valve O rings, anyone interested since there is a minimum order on the smaller ones?

Thank y'all in advance for any help! :D

SLS system references are in the W123 and W126 FSMs under section 32-501 through 32-741.
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/chassis_81_to.htm

https://www.startekinfo.com/StarTek/outside/12253/disc%202/program/chassis_500SEL.htm



There is a reference in the Note on 32-501 page 32.3-504/1 "(for checking vehicle level - refer to 40-300 and 40-310)". These jobs are located in the W126 FSM.

"Permissible difference vehicle level measured between left and right side of vehicle" is 8 mm with special tool, 15 mm with tape measure. Job 40-300 page 952.
https://www.startekinfo.com/StarTek/outside/12253/disc%202/program/Chassis/40-300.pdf

https://www.startekinfo.com/StarTek/outside/12253/disc%202/program/Chassis/40-310.pdf

Happy wrenching :)

Thank you so very much for the help! :D

Notice how per usual, Startek is severely lacking. Not anywhere does it specify ride height for a W123. Those it does specify, have to measure off the suspension and preferably with a special tool. At least though does confirm something not to specification with more than a half inch difference side to side.

More important is obtaining the F.S.M. without the C.D., which is only usable on Microsoft Windows O.S.. Thanks to you, read through all them except for the 107.

I rebuilt the SLS in my '85TD in 2007... still going strong. 2014... I put in new Rear Struts.
Ride height... is and always has been 13.25" from Center Star to Fender Well ...with no load and empty fuel tank or 600 lbs load and full fuel tank. There are Coil Spring Pads of different thicknesses which can lower or raise the ride height by about 1/4" .

Dennis, than you so very much! :D

12 1/2" and 12" with one gallon of fuel, so no wonder looks saggy. If the most is 3/4", that only gets half way. Then put a tank of fuel in and bet drop at least half an inch, if not a whole inch.

Again, so glad to have it confirmed saggy springs.

Had to put down Grandmother's old cat yesterday, clean the house, then today deal with insurance and taking the cat down to be cremated. Hopefully tomorrow can get at it.

This sounds like a broken spring.

There is a Mercedes part number for a rebuild kit from dealers for the valve.

If the problem is sagging overnight sometimes just renewing the fluid can correct that if it is really full of debris.

The baseline pressure contribiting to static ride height is due to a metal to metal interface in the valve and debris can allow fluid to slowly "leak" instead of holding steady overhight.

There is a Mercedes guy in Oak Ridge TN to thank for that tidbit.

Performance Analysis | Climate Control | Diaphragms | Blower Motors | Pushbutton Panels | Vacuum Door Locks | Autotemp | Cruise Control | Engine Oil Analysis | Mercedes-Benz Parts | Mercedes-Benz Club of America | Oak Ridge | Car Care

He has put together a kit he sells with components needed to rebuild the radial piston pump. I think the O rings are viton in his kit.

spring struts are now available for less than $100 each from dealers who ship parts for 25% off list price.

The rear end never changes height, even with about 200 pounds of load, meaning warn springs. Plus with the out of tolerance side to side, springs no longer in specification. Therefore mist be replaced.

Renewed, flushed, the fluid and no change in ride height or response.

Plan was to avoid the pump for now. If rebuilding the control valve does nothing, then do the pump.

I have springs for all four corners, but only doing the rear for now as no compressor.

adjust the ride height valve maybe

those pumps stop putting out pressure needed to do the job after the Orings are old, loose resillience, the high pressure fluid blows right by the Oring into the low pressure feed area so there is no output pressure

if so, rebuild kit from performance dynamics

its easy

you'll need a bamboo chop stick or a plastic one to help get it apart