R129 ads 500sl

[jonclemett]

Searching underneath my '92 500 to try and find the source of a problem with my ADS I noticed a plastic lever arm switch under the rear axle, there is a couple of inches movement and I can feel a click when I move it up and down - does anyone know what this does?, is it part of the ADS?

 

[BTB 500]

Sounds like that could be the rear ride level sensor. If so it should be connected via a pushrod to part of the suspension (roll bar maybe) ... it tells the ADS unit how high the back of the car is. There's another one at the front, on the offside suspension.

If the connecting arm is missing that will definitely be a problem!

 

[BlackC55]

It is a switch that when activated releases the pop up roll bar.

 

[jonclemett]

Thanks Black, I will continue searching elsewhere for the problem

 

[EDZ649]

The rear level control valve is located approx in the middle of the rear axle or thereabouts. You should be able to see the hydraulic pipes leading from the rear shocks to the valve.

 

[BTB 500]

Sounds quite different to the ADS II on my car then. That has electrical ride-height sensors front and rear, rather than valves.

I adjusted the linkage to the front one to lower the front suspension slightly.

 

[grober]

My guess is that you might have a problem with the rear spheres which have lost nitrogen or the internal diaphragms are leaking?

 

[EDZ649]

Sounds quite different to the ADS II on my car then. That has electrical ride-height sensors front and rear, rather than valves.

I adjusted the linkage to the front one to lower the front suspension slightly.

Mine has ADS II Bill.

 

[BTB 500]

Pretty sure mine doesn't have hydraulic valves underneath to do the levelling, but I'll have another look some time!

OP's car (1992) would have ADS I, which I think did have some significant differences.

 

[jonclemett]

Thanks everyone for all the advise so far, I think I will take some pictures of the switch on the weekend and post them on the forum, I don't really want to fiddle with it if it is part of the anti-roll bar mechanism, especially with the hardtop on.
With regards to the spheres - re grobers reply - should the ride go bouncy if this were the case?, the car seems to still ride ok, also can the fail quite so quickly?, one day it was fine the next it was sitting low. When I got it back from the MOT station the fluid in the front reservoir was way above the max limit, this is something I would have noticed as I check it meticulously.

 

[EDZ649]

If the spheres have gone the ride will be rock hard and skipping around all over the place.

 

[grober]

OK now you have said a little more about the circumstances of the "failure" my guess is that the MOT tester has disturbed the rear axle level control linkage which is normally attached to the rear antiroll bar. They may have tested it with a pry bar- which is pretty standard when looking for worn bushes on the rear suspension links at MOT time but not something you would do to the more delicate level linkage! This has caused the car to "think" its higher in the air than it actually is- it has then lowered the car possibly to its lower limits via the hydraulic struts this has caused the fluid level to rise in the reservoir due to the reduced system volume [ shorter struts] You can only really check this by inspecting the car properly up on a ramp.
ps if the hydraulic struts are at the end of their design travel I would be wary of using the car in case the suspension elements get damaged.

 

[jonclemett]

Thanks Grober, I feel your comments regarding the MOT testers "enthusiasm" could well be a problem, they are certainly not Mercedes experts and probably did not even know that the car had hydraulic suspension plus it would explain the reasons why the car was great when I took it in and low when I picked it up. I will try and find someone who has a ramp I can borrow - if you or any other forum members could help me in regards of exactly what I should be looking for I will be very grateful.
I have to say at this juncture that these dedicated Mercedes forums are an excellent source of information and help,the breadth of knowledge available massive. Will keep you posted

 

[grober]

Have a look at this section of the rear suspension parts. http://www.auto-parts.spb.ru/cat/cats/m.mycat?Form set up might be slightly different on your car but you are looking for a linkage between the rear antiroll bar and a hydraulic proportioning valve. As the ARB rotates it operates a lever arm on the valve causing the suspension to maintain one of 3?? set levels. If you find anything post some pics which may help identify exactly which system you have.

 

[jonclemett]

Thanks Graeme, could you just check that link for me please, it is saying site does not exist.
Cheers Jon

 

[Will]

Is it possible that something may have been disturbed during the newer MOT 'shakedown' test on the suspension? The newer testing stations use a vibrating platform that really shakes the car about to check damper operation, worn bushes/joints etc.

If the hydraulic level has risen, and the car is sitting low it must be an issue with the struts not being fed enough fluid to raise to the correct height.

I've never had to look at the ADS system, but I would imagine that there would be hydraulic valves to control the flow of fluid to the front and rear struts.

Would it be easiest to pop back to the garage and have a look on the ramp?

Will

 

[grober]

try this.
REAR TORSION BAR & HEIGHT CONTROL VALVE USED SELF-LEVELLINGDEVICE

 

[jonclemett]

Thanks Will, I do intend to go back to the garage at some point but I want to try and pinpoint the problem as best I can first, the garage concerned wanted nearly £3k just to fit new cats hence I don't think the had my best interests at heart, if I can prove that they may have been negligent that I can then ask them to repair the problem foc.
Regards,
Jon

 

[jonclemett]

Cheers Graeme, that is clearer now, will take a look as soon as I can find a ramp.

 

[jonclemett]

Hi all,
I have found the problem!, Please see images attached - there is a "unit" attached to the control arm which has sheared at the bottom where it attaches, it seems like an easy home replacement, just one nut at the top and one at the bottom plus to pipes to undo on the actual body of the "unit" - does anybody know what it is called/part number etc? I did rest the 2 sheared ends together and gently lowered the car and hey presto, suspension height was restored!