[Pazo]

Hi!

I’m running out of ideas, what might be wrong with my 1993 500SL ride height control. Maybe not crucial since our friends with ADS in the US have always done without (presumably due to contemporary US bumper height regulations). But since everything else works as designed in my SL, I have made several futile attempts to fix even the height control.

When the button to the left of light switch is pushed, red indicator LED lights up and there is an audible click from ”Y36” control solenoid close to right front wheel. But the ride height does not increase. According to Daimler, a European market car with ADS has about 30 mm increased height when speed is below 48-52 km/h, with Raised Ride Height setting on.

Some background: ADS suspension works very well but the height control has never worked when I’ve had the car. When I acquired it, one pressure sphere was ruptured, so I replaced all four of them. I have also fixed the usual leaking O-ring seals in the ADS control valve. Also I have checked that the ride height control rod regulating pistons have not seized. I even opened the Y36 height control valve; it was slightly stuck with dirt/sludge. I was optimistic cleaning would finally fix the issue but that was not the case. There are no fault codes in DTC memory. The car was built and delivered to German market 4Q1992.

I have browsed lots of forum threads but find very little about the ADS 1 ride height control – maybe because US cars do not have it at all. Guidance would be greatly appreciated to finally identify, what could be the root cause of this problem. See attached schematic picture explaining the ADS 1 main control valve. How do the encircled components look like in reality? Anyone has a photo?

 

[GUSMB]

When you push the height control button the actuator connected to the sway bar should move the height control valve (not to mix up with the main control valve), check this, also, disconnect the actuator and see if you can raise it "manually" with the arm on the height control valve, just to make sure it works in general.

 

[Pazo]

The root cause is finally found. In the height control valve, there is a sintered bronze filter in oil inlet (see attached picture). After 25 years, no oil pressure could pass through. It is not a good design since inevitably, the height function will become slower and eventually stop working when over time dirt accumulates to the tiny sintered filter.

The ride height setting is a „nice to have" feature, so most owners do not bother. And it is hard to detect from driver’s seat, whether the car lowers 15 mm at speeds over 120 km/h as specified. I drilled the clogged filter away. ADS1 has a nylon filter in the oil reservoir but it is not capable to arrest small particles.

Another potential fault is, if the 4 mm ball bearing with small piston in oil channel „S" gets stuck. When oil pressure from pump moves the sliding valve, the three 4 mm steel balls move down and protrude back again about 1/3, when the sliding valve retards (after engine is off and oil pressure drops). If the small piston is not moving freely, remove the tiny grub screw to access it from both sides; use e.g. thin wires until it moves freely against spring load. Two balls control the oil return from the front & rear self levelling valves. The third steel ball delivers operating pressure from the front accumulators to ride height control valve (Y36, absent in US models).

If height control has been unused a long time, oil pressure pistons in height control rods under the car may have jammed - as GUSMB points out below. It is a rather simple system and a DIYer can clean the rod pistons and seals (prices of new OEM rods are insane, over $500 each).

 

[GUSMB]

Great job!

I never got around to fix one with the manual height issues since I have a US spec nowadays.

 

[Guilherme Rocha]

The root cause is finally found. In the height control valve, there is a sintered bronze filter in oil inlet (see attached picture). After 25 years, no oil pressure could pass through. It is not a good design since inevitably, the height function will become slower and eventually stop working, when over time dirt accumulates to the tiny sintered filter.

The ride height setting is a „nice to have" feature, so most owners do not bother. And it is hard to detect from driver’s seat, whether the car lowers 15 mm at speeds over 120 km/h, as specified. I drilled the clogged filter away. ADS 1 has a nylon filter in the oil reservoir but it is not capable to arrest small particles.

Another potential fault is, if the 4 mm ball bearing with small piston in oil channel „S" gets stuck. When oil pressure from pump moves the sliding valve, the three 4 mm steel balls move down and protrude back again about 1/3, when the sliding valve retards (after engine is off and oil pressure drops). If the small piston is not moving freely, remove the tiny grub screw to access it from both sides; use e.g. thin wires until it moves freely against spring load. Two balls control the oil return from the front & rear self levelling valves. The third steel ball delivers operating pressure from the front accumulators to ride height control valve (Y36, absent in US models).

If height control has been unused a long time, oil pressure pistons in height control rods under the car may have jammed - as GUSMB points out below. It is a rather simple system and a DIYer can clean the rod pistons and seals (prices of new OEM rods are insane, over $500 each).

First of all, great info my friend.

I am in the process of buying a 92 500SL with ADS just like yours, also built in Germany but at 12-1992.

I have 1 question for you: does your car raise/lower while on park? I have not driven this car yet and having in mind the light in the cluster for the ADS is taken off, I can't figure it out. Lack of information, like with you, is my main problem.

No light regarding the sport mode or up/down should light up while idling in park?

Thanks

 

[Guilherme Rocha]

The root cause is finally found. In the height control valve, there is a sintered bronze filter in oil inlet (see attached picture). After 25 years, no oil pressure could pass through. It is not a good design since inevitably, the height function will become slower and eventually stop working, when over time dirt accumulates to the tiny sintered filter.

The ride height setting is a „nice to have" feature, so most owners do not bother. And it is hard to detect from driver’s seat, whether the car lowers 15 mm at speeds over 120 km/h, as specified. I drilled the clogged filter away. ADS 1 has a nylon filter in the oil reservoir but it is not capable to arrest small particles.

Another potential fault is, if the 4 mm ball bearing with small piston in oil channel „S" gets stuck. When oil pressure from pump moves the sliding valve, the three 4 mm steel balls move down and protrude back again about 1/3, when the sliding valve retards (after engine is off and oil pressure drops). If the small piston is not moving freely, remove the tiny grub screw to access it from both sides; use e.g. thin wires until it moves freely against spring load. Two balls control the oil return from the front & rear self levelling valves. The third steel ball delivers operating pressure from the front accumulators to ride height control valve (Y36, absent in US models).

If height control has been unused a long time, oil pressure pistons in height control rods under the car may have jammed - as GUSMB points out below. It is a rather simple system and a DIYer can clean the rod pistons and seals (prices of new OEM rods are insane, over $500 each).

First of all, great info my friend.

I am in the process of buying a 92 500SL with ADS just like yours, also built in Germany but at 12-1992.

I have 1 question for you: does your car raise/lower while on park? I have not driven this car yet and having in mind the light in the cluster for the ADS is taken off, I can't figure it out. Lack of information, like with you, is my main problem.

No light regarding the sport mode or up/down should light up while idling in park?

Thanks

 

[Pazo]

Hi!

The car rises when parked. Both the height control indicator by headlight switch and the comfort/sport mode on the center console are illuminated when selected (ignition on). At idle the car rises slowly but if you increase RPM to around 2000, it is easy to observe. The elevation is about 30 mm.

For sure the ADS cluster light is removed for a reason; read all the fault codes so that you know what is wrong! Note that most hydraulic faults like e.g. a punctured pressure sphere do not throw DTCs. But electrical faults in the Adaptive Damping System are fairy well covered.

Hope I managed to address your question Guilherme? Good luck with your acquisition!

 

[Guilherme Rocha]

Hi!

The car rises when parked. Both the height control indicator by headlight switch and the comfort/sport mode on the center console are illuminated when selected (ignition on). At idle the car rises slowly but if you increase RPM to around 2000, it is easy to observe. The elevation is about 30 mm.

For sure the ADS cluster light is removed for a reason; read all the fault codes so that you know what is wrong! Note that most hydraulic faults like e.g. a punctured pressure sphere do not throw DTCs. But electrical faults in the Adaptive Damping System are fairy well covered.

Hope I managed to address your question Guilherme? Good luck with your acquisition!

Hey there, thanks for the fast reply!

The car is a 92 Euro 500SL with ASR, ADS, CC, both memory seats and orthopedic driver, etc etc but has a 90/92 300SL US-Spec cluster. I think it problably broke one time and they just put whatever they could found. R129's are very rare around here (Portugal) and most of them are 300's.

When car is running in park, ASR light works in center console but, both sport mode and go up/down button close to the light switch do not work. The good bits: the car runs smooth and the suspension is leveled as it should. Also, no leaks what so ever. I did not check the main pump for leaks, is it really under the spare tire in the boot? Checking codes problably wont be possible, since it's in a used car lot. (BTW did it in my 300E 2.8 before buying and still had to replace so much stuff lol)

 

[Pazo]

Hey there, thanks for the fast reply!

When car is running in park, ASR light works in center console but, both sport mode and go up/down button close to the light switch do not work..... I did not check the main pump for leaks, is it really under the spare tire in the boot?

Be aware that if ADS has a fault, damping defaults to hard that is at least for me far too uncomfortable. And most benefits of the "skyhook" ADS suspension are lost.

The oil pump under spare wheel delivers operating pressure for roadster soft top and roll bar. The tandem pump in engine bay delivers oil pressure for power steering and suspension (it is actually two oil pumps on a single shaft).

Cheers!

 

[Maukku1955]

Hi,
I just replaced all seals and O-rings due to leaking top plug on ads-valve on my SL600 European ADS1 system.
When I parted the valve, there was 3pcs 4mm steelballs dropping on my desktop. As I have researched the forum and pictures, I have seen only two 4mm balls on the slide valve, which operates the check valve?
When I assembled the valve with 2 pcs 4mm balls, one bigger spring loaded ball and one very small on the Y37 solenoid, the car rised, but does not go down.
I did not bleed the system yet, but I guess air is not the problem.
Does anybody know what went wrong, when the front shocks will not bleed?
Thank`s

 

[Maukku1955]

...here is the assembly from Gus, that I followed. Picture no.16:

https://www.garaget.org/forum/viewtopic.php?id=281523&pid=3892326#p3892326

 

[bobterry99]

I did not bleed the system yet, but I guess air is not the problem.

Air could be and in fact likely is a problem. You need to bleed air from the pump by running the engine for a few seconds with the line from the pump to the valve block disconnected.

 

[Maukku1955]

Thank`s, bobterry99, it will be the first thing to do tomorrow.
I have dismantled and assembled the valve two times now, hopefully just air in the system.

 

[Pazo]

… When I parted the valve, there was 3pcs 4mm steelballs dropping on my desktop. As I have researched the forum and pictures, I have seen only two 4mm balls on the slide valve, which operates the check valve?
When I assembled the valve with 2 pcs 4mm balls, one bigger spring loaded ball and one very small on the Y37 solenoid, the car rised, but does not go down.
I did not bleed the system yet, but I guess air is not the problem.
Does anybody know what went wrong, when the front shocks will not bleed?

There are three 4 mm balls of which one is under the 13 mm screw (on top of GUSMB's picture). So when you assemble the sliding piston, put two 4 mm balls into the piston bore and then - when piston is in place - insert the third 4 mm ball, then bigger ball, spring and 13 mm screw.

In addition, there is a very small ball for the sink stop valve Y37 solenoid.

If you have assembled the valve with only two 4 mm balls, it will not work correct!

 

[Maukku1955]

Thank`s so much Pazo, I was so happy about your post to finally get solved with this missing bearing!
The valve was fixed today and pump bleeded by the pressure connection.
However, the car does not raise.
I think the pump bleeding is not enough, have to bleed the valve tomorrow.
But things are getting better, car is driveable, suspension works, no hydraulic leaks and no surplus parts.

 

[Pazo]

Thx Maukku1955!

A simple way to verify pump oil flow is to loosen the return pipe from reservoir. Attach a short flexible pipe and check that oil is coming out at idle. Note: the oil flow is rather slow.

While bleeding ADS 1, open the valve "50a" in distributor with 10 mm spanner one turn or so. This valve just opens oil flow between the front and rear axle circuits. Bleeding is straightforward but be patient; getting the car up takes time. You can increase rpm to speed up. Maintain oil level in the reservoir. When the car is driveable again, rest of the air gets out by driving around on bumpy roads.

Good luck! Pls report back.

 

[Maukku1955]

Thank`s again for the proper procedure.
Now I have cold beer in my hand and sauna on heating in order to get rid of all hydr.oil I have been soaked in a couple of days.
I will reply tomorrow.

 

[Maukku1955]

Now the main valve was bleeded, no cure.
Then I disconnected the level adjustment cylinder and operated the arm on the main valve manually. The valve works, car rises and lowers nicely!
The fault seems to be solenoid Y36.
There is no current (12v?) when the level adj. switch is pressed left to the head light switch. The red led illuminates however, but no voltage detectable on the solenoid pins and the height adjustment cylinder is not working.
You wrote earlier, that there should be an audible "click" when the solenoid engages.
But good, the valve works, now it seems to be electrical issue.
now, back to the car...

 

[Maukku1955]

some update: I was measuring the voltage again, and now there is 16V. No audible "click" but something happens inside the coil. Now I have to get pressure to height control cylinder. It was bleeded also.

 

[Maukku1955]

I started to wonder, if the item no 50 "regulating piston" is wrong way in its bore between those often leaky plugs.. That is the small piston with one end slotted.