Failed ADS air cell on 1999 SL?

[TimboL]

I have a 1999 SL (129) that recently developed a 'clunking' noise somewhere at the back. It's only noticeable at low speeds, and it sounds as if it ought to be a part of the exhaust system knocking against something. I had the car inspected by my favourite dealer and they were not able to find any sign of anything chafing, although they were able to hear the noise on a road test.

Today, when I went to top up the screen-wash reservoir, I noticed the car had swallowed the entire contents of the ADS hydraulic fluid reservoir, although there is no sign of any leakage on my garage floor. I've topped up the hydraulic fluid and been for a drive, and there is definitely not a catastrophic leak.

The suggestion is that the seal between the air and oil compartments in one of the ADS air cells has failed, and it is the failed ball that has consumed the hydraulic fluid.

Is this suggestion plausible? The car does not feel any different to drive compared with how it has ever felt. Is there any way of finding out which ball has failed and therefore whether it is the front cells or the rear pair that need replacing? Might the clunking sound at the back be indicative of a failure at the rear?

I realise it would be sensible to replace all four air cells at the same time. However, at £125 ex VAT per ball, plus something like five hours' labour to fit all four, I don't really want to spend a load of dosh on something that's not absolutely necessary. I know the car is getting rather old and likely to have even more problems than when it was new, but I just happen to rather like it and I haven't got the heart to rid of it.

Edited by TimboL on Friday 5th October 20:48

[Pentoman]

You sound like you know a bit about what goes on underneath a car (this is not usual for pistonheads!) - I'd point you to Mercedesshop.com where it is normal and they could well help and would understand your question unlike me! They even have an SL-specific forum.

[dazren]

Common problem with age. Happened to our old 1990 SL. I'm guessing the suspension at the rear has gone hard?

[TimboL]

Thanks for the replies.

dazren said:

Common problem with age. Happened to our old 1990 SL. I'm guessing the suspension at the rear has gone hard?

I have been told it is pretty common with age. But the odd thing is the suspension and damping don't feel any different to how they have ever felt. I usually drive with the ADS in the firm setting to stop the car rolling around so much, and I wouldn't say the rear feels any harder than usual. If you lean on the corners, the car is still springy all round.

Pentoman said:

You sound like you know a bit about what goes on underneath a car (this is not usual for pistonheads!) - I'd point you to Mercedesshop.com where it is normal and they could well help and would understand your question unlike me! They even have an SL-specific forum.

I don't really know much about it at all, only what a technician at the dealer explained to me when he showed me the duff air cells that he had just taken out of another car. Thank you for the pointer to Mercedesshop.com . I will have a look there.

[GregE240]

dazren said:

Common problem with age. Happened to our old 1990 SL. I'm guessing the suspension at the rear has gone hard?

Now mine!

Father experienced the same with his Bentley Brooklands (which utilises exactly the same suspension - it is badged as Active Ride). Turns out it was a suspension sphere, cost for the part was less than £100 and about an hours labour.

Mine has had at least both spheres at the back replaced in its life.

HTH
Greg