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· Registered
2 Posts
Discussion Starter · #1 ·
Hello all, I am looking at buying my first classic car and interested in the R129. I have opportunity to buy a 1990 300SL that originally came from factory with ADS1 as optional extra.
The car is in excellent condition based on photos, videos, service history, independent inspection. Car is one owner and for sale now through a reputable trader\seller. The seller advises that the one owner had the ADS disabled to avoid potential ADS related issues.

Up to a few weeks ago, I knew nothing of R129s and ADS but have trawled enough forums\posts to get a basic understanding and to also get understanding that while ADS1 is excellent when working correctly, it also sounds a potential nightmare to resolve if it goes faulty.

Regarding the 1990 300SL I am looking at, the seller says it drives very well (I believe him) and independent inspector also says drives well (albeit a short test run). What I don't have is details on what exactly "ADS is disabled" means in relation to this car.
  • What I do know is:
    • The hydraulic dampers are all in situ & plumbed
    • The soften\stiffen button centre console) seems to have an effect
    • The ride height button (beside main light switch) does not have any effect
    • The ADS Warning Light comes on with ignition & goes out when engine starts
I am hoping some forum members who have built up very hard earned knowledge on ADS1 could help with some advice:
  • Is it possible to just disable the manual ride height option (the function that is driver operated via switch beside the headlight switch)?
    • If yes, what elements of the ADS1 would you expected to find removed\disconnected\decommissioned?
    • Also if yes, would disabling this functionality result in expected less maintenance\potential issues & how?
  • What questions should I be asking in relation to the working parts of the ADS1 that seem to be on the car?
    • Nitrogen spheres replaced? Fluid replaced? etc?
  • What tests can be done to check the ADS1 is actually working as expected?
I guess next question I have which I know will be matter of varying opinion, but would like to hear views on buying a 30 year old car with ADS1 (assuming the ADS elements have been well maintained and any elements disable have been done correctly). Or if you had a choice between 2 similar condition R129s - 1 with ADS, 1 with non ADS - which would you recommend?
I am a reasonably competent DIYer but looking to get a car that is in very good condition and do more driving than major maintenance work.


· Outstanding Contributor
2005 SL600, (2) 2003 SL500
4,604 Posts
I own an ADS I car myself, George, and will answer some of your questions. Also, there's a chap who goes by "Pazo" that knows quite a bit about these early ADS systems and has posted some good documentation to the forum over the years.

It would be possible to disable manual ride height control simply by removing specifically one of the two fuses installed atop the overvoltage protection relay (OVP). The OVP has a red top with a clear plastic cover and is located in the right-rear engine compartment among the various vehicle electronics. The only logical reason to disable the function would be that it wasn't working properly and was adjusting the level of the car independently of the control switch.

I would ask how old the nitrogen spheres are and if the front and rear level control valves have ever been serviced -- if they have not, this would not concern me.

I may reply with more later...

· Registered
500SL ('93), C200 ('14), MGB Rdstr ('65)
305 Posts

I would not recommend anyone acquire a R129 with ADS if she/he is solely dependent on repair shops (actually, IMO that goes for any old Benz model regardless of equipment). ADS1 delivers good ride quality. A benefit is that you can easily set ride height according to your personal taste. It is reliable and straightforward, once you learn it and fix as soon as a fault arises.

However, it is difficult to find mechanics that understand ADS - MB dealers are nearly useless but they are still very competent in writing huge bills. You say you are “a reasonably competent DIYer” so I believe ADS can be ok for you.

Replacing pressure spheres is comparable to replacing conventional shocks in terms of labour and cost.

You did not mention whether the indicator lamp in manual height control lights up when selected. That would mean its electrics are maybe ok.

The early ADS has no oil filter except a tiny one for manual ride height selection (non-US cars). During decades dirt will accumulate to the filter, manual height control becomes slower and eventually stops working when the filter gets clogged.

If(?) height control is disabled, maybe it had a leak? The rest of the suspension is independent of the manual height control; US cars did not have it at all. It is just nice to have on bouncy country roads and steep driveways.

With the information at hand, it is impossible to guess, what has been disabled in the ADS. However, it seems that the ADS ECU is working. Since the car drives well, unlikely that any of the spheres is shot. Is contacting the previous owner an option?

To diagnose, it is imperative to read fault codes. You need only a simple LED blink code reader and ADS1 covers electrical faults pretty well. For hydraulics, look if there are any leaks (valves, plumbing, struts, rods).

Hope I managed to address your questions?

· Registered
2 Posts
Discussion Starter · #4 ·
Hello Bobterry & Paso,

Thanks for the reply and good info. I can see from your posts re ADS that you are probably more intimate with ADS1 at this stage than most if not all at MB.
This is a UK car, one owner who unfortunately died a few years ago and car has now been sold on by the family to the reputable seller that is now offering for sale. I have asked seller if they can provide details on specific maintenance of the ADS system over the years and also any specifics on what element has been disabled & how.

So far the only element that appears not to work is the manual height adjust (I will check but believe the LED light does not come on when the switch is pressed). Ideally I would inspect myself but I am based in Ireland and now with Covid 19 restrictions it is not so easy to travel to UK & back for non essential reasons (Some would say classic cars are essential but you might not be faced by an enthusiast at border points!).

My indy inspector was general car mechanic, not specific specialist in MB or ADS - He checked no obvious leaks (but not checking all valves, etc), ride stiffen seems to work, drives good.
Sounds like a decent checklist would be:
  • Specific ADS service history - what should I expect to see in a 30 year old with 98K miles?
    • Spheres replaced within last 10 years?
    • Fluid Changes & when?
    • All control valves serviced - How many are there & what do they do?
    • Any other service items?
  • Current read out of fault codes
  • Hydraulics: Check if there are any leaks (valves, plumbing, struts, rods).
  • If any element disabled - Why\How\When\Who ?
  • Check if manual height led comes on when switch pressed
  • Any other checks (to try to avoid cheques..) that I should consider?
It also sounds that from your replies that disabling the manual height option would not avoid ADS issues other than issues with the manual height option itself? i.e. disabling manual height would not prevent issues with dampers, spheres, control valves, etc - am I reading that correct from your replies?


· Registered
500SL ('93), C200 ('14), MGB Rdstr ('65)
305 Posts
Even if dirt is the number one enemy of ADS1, Daimler considered it maintenance-free; there was no servicing. So probably, you cannot find any (ADS) service records or fluid changes.

In my thinking, spheres are consumables. Good to know, when they were changed though.

Maybe the seller can send you photos from the underside – from potential leak points?

In ADS1 there are three valves. The main control valve with oil distributor and one level valve for each axle.

The stories I have read of “disabling” ADS is conversion to iron suspension; the springs and shocks were swapped from a non-ADS car. Spheres and some plumbing may still be there. In such case I’d walk away - the car is molested and no longer collectible.
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