Workshop Q&A Helpdesk
Steve Rothwell answers more of your technical questions, this issue ranging from squeaky brakes to intermittent wipers.
Q
I would like to ask your advice on my 1978 Mercedes 250T estate ( W123). The problem I have is that the car – even with no load in it – sits very low at the back. The suspension also feels very solid over bumps and dips, and fails to help smooth the ride out. I have been told that the problem may be due to a valve in the rear suspension, but that is about the extent of the information I can find. I know that the suspension should be self-levelling, but didn’t want to start trying to fix it before I fully understood it.
Mike Hughs
AThe self-levelling suspension on your Mercedes is a complex system and quite importantly would need to be de-pressurised before you could begin to consider replacing any components. To de-pressurise the system you will need to slacken the bleed screw on the level control unit and drain off around ½ litre of fluid. When re-pressurising the system, you will need to top the reservoir back up and then, after disconnecting the link to the level control unit, move the lever fully upwards running the engine for 30 seconds or so at around 2500rpm. The vehicle will of course need to be jacked up to prevent it dropping down fully.
Having told you how to depressurise and the re-pressurise the system, the problem still remains as to what components you will need to change. I have assumed that you have no leaks which would be apparent, and providing the rear of the vehicle is not bottoming out we can assume that the pump and levelling valve are both working. This leaves the accumulators and struts. A failed strut will normally give a bouncy ride as opposed to the hard ride you have, so by a process of elimination this would suggest that the accumulators are the problem with your Mercedes.