I used Google Translation, combined with my ancient knowledge of Deutsche (last time I really translated was in 1965 to pass requirements for technical doctorate) to bring the prose of this document to those who do not read/understand German. It's a bit long, and some duplication. (I made a couple of comments - in purple).
Mercedes Benz ABC Suspension
Our company has specialized on the ABC suspension for years.
We diagnose , repair, and replace all components in the ABC suspension.
For questions please contact our phone number. We are happy to help and assist you with tips and tricks that work.
What is the ABC suspension?
The ABC suspension is an electro-hydraulic active system combined with a coil spring.
The Active Body Control (ABC) can compensate within milliseconds to the rolling and pitching movements of the body when starting, braking and cornering. The ABC is thus superior to air suspension systems.
Care of the ABC system:
The ABC suspension has a gotten a bad reputation because many owners do not maintain it, and critical components become damaged – eventually destroying the whole system. Regular maintenance results in an ABC suspension with the same life expectancy of the rest of the vehicle. Below you will find some hints from our experience.
If it is operated for years with the original hydraulic fluid, or after this fluid has become dirty, then many if not all of the components of the ABC chassis can be destroyed. OR if it is operated with low fluid levels, the owner will have the same result. This includes the hydraulic pump, struts and valve units.
You can easily check your oil quality using the dipstick from the reservoir. This sits next to the fill cover which contains the white filter. Take a white lint free towel and pat the oil from the dipstick onto it. Clean oil is green, light brown in ‘fair condition. IT SHOULD BE REPLACED BEFORE IT BECOMES DARK BROWN OR BLACK. If it is very dark brown or black, replace it immediately (or be prepared to replace expensive components).
The system uses about 15-16 liter of Pentosinöl (A00198924003-10, or Pentosin CHF 11S). To replace you will need about 10-12 liters. This will replace MOST, but not ALL the hydraulic fluid, as some will remain in the individual spring reservoirs.
But, that is not a major problem. The large amount of new fluid mixes with the small amount of old fluid. You will also replace the filter in the ABC reservoir with the new 3mm filter. This new fine filter will clean the resulting fluid mixture. After about 750 -1500 miles you should once again flush/replace both the Pentosin fluid and the 3mm filter. Then you should end up with only clean/green fluid in the system. ( Anleitung_Spülen pdf. )
In one of the pictures you can see an additional filter, which we developed. This magnetic filter is specially designed to trap metal abrasion particles that can come from components of the ABC chassis. These metal shavings are caused when old ‘dirty/abrasive’ fluid flows through the ABC hydraulic pump, causing mild to severe erosion of metal. This magnetic filter removes any future metal abrasion or metal chips from the fluid, thus protecting the whole system (the fluid is repeatedly flushed and cleaned with every circulation through the reservoir).
Once metal shavings are created, they can infiltrate the entire system, making it necessary to disassemble the entire system and clean by hand!
The installation of the magnetic filter will help prevent this from happening. With the crystal clear case, as you open the hood, you can readily see and check the color of the ABC fluid and observe whether any metal has been collected by the filter. The filter is washable, so you make a one-time purchase. In the rare event that somehow something gets broken, all parts can be ordered individually.
CLEAN OIL is important for the long term durability of the ABC system
In the first picture you can clearly see an ABC pump that has run 120,00 miles in the clean ABC system looks like. In the pictures below, the pump has been running about 48,000 miles, and the fluid was very dark brown. The metal debris in the oil has produced fluid that is the equivalent of liquid sandpaper – which has rubbed and damaged everything - with every mile that was driven. Moreover, with this abrasive fluid, more friction occurs in the system, especially in the ABC pump. High friction means more heat. On some occasions pumps have become so hot that they overheat and glow! When this occurs, EVERYTHING DETERIORATES your fluid becomes progressively worse and begins to smell like burnt oil.
If the Pentosinöl in the ABC system is renewed every 15 to 30K miles, or every ~3 years, depending on load and driving style, the ABC system should last for 300,000 miles or longer.
This longevity has been proven by our own car and the maintenance we have done on it. This car is a W215 CL 65 AMG V12 Biturbo, and after about 6K to miles the fluid begins to turn brown. After 12K miles it is dark brown.
For vehicles with less engine power, it may take longer. But we have found the fluid usually starts to turn a dark brown to black color after ~18-25K miles. For vehicles that are have not had adequate service to the ABC system can change color even faster after the first flush/change.
We have driven our frequently used 2003 W220 S Class long version S55 AMG Kompressor ~250K miles. We have changed the ABC fluid approximately every 18K miles. All suspension components on this car are original except for 2 dust covers for rear shocks and a pressure hose to the right front strut. AND, the ABC pump from our vehicle had after all these miles is still ~190 Bar (~2,850 PSI) at operating temperature.
Our latest acquisition an S Class W220 S65 AMG V12 Biturbo long version 25K miles. The Pentosinöl was black as tar.
We had to disassemble everything clean and repair many components.
At this point, it is important - both for vehicle owners with ABC suspension (and Mercedes shop foremen and those who want to be) – to remember that the Pentosinöl has properties similar to brake fluid. They are both hygroscopic meaning they absorb water, such as from the air. Therefore, it is IMPORTANT that the Pentosinöl is replaced after a maximum of 5 years to prevent corrosion in the suspension components. (here they state this time interval is also recommended by Mercedes Benz – certainly it is for brake fluid, but not clearly stated for ABC fluid as far as I know).
For this reason alone, this fluid is not maintenance free as is always claimed by the MB dealer. You can check about the hygroscopic effect under brake fluid at Wikipedia.
Pentisol is hygroscopic, like brake fluid it absorbs moisture and deteriorates!
We found one incident where a SL 55 AMG was stored in October and brought out for driving in April. During the winter, the pistons had rusted in the ABC hydraulic pump. When first started, the pump was destroyed and there was, within seconds, a red error message on the instrument cluster.
"ABC defective please visit workshop". If that appears, the pump pressure is below 100 bar. At any pressure of 99 bar or lower, this red error message appears and the car DEFINITELY should not be driven further.
ABC pumps and systems are ONLY destroyed by bad fluid!!
The ABC pump is lubricated by the Pentosinöl and 200 bar pressure which it produces. This fluid passes through micro sieves and around and through very small passages to the main shaft and main bearings. Contaminated fluid first contacts the screens. These become partially plugged, and as a result the main bearings are inadequately or not at all lubricated. Then, the pump starts making bearing noise. When that occurs, if you then press the ABC button for lifting and your vehicle goes up. During the raising of the vehicle the ABC pump is quiet for a short time. When it reaches full height, the pump becomes loud again!! Reason for this is that during the lifting operation, the main shaft is pressed under load into the main bearing, so the ABC pump for this moment is quiet. When the vehicle is at full height the load is no longer holding the main shaft to the bearing. Thus, the main shaft is rattling in the main bearings because the fluid pressure/film is missing.
IF the wear of the shaft and bearing is advanced, the pump is constantly loud.
It also happens that if the oil supply rapidly goes to zero, then the main shaft overheats the main bearing and they VERY RAPIDLY wear on each other. The pump is ruined. In these cases, repair is not possible. The pump housing is useless because the bearing seats are damaged in the pump housing and new bearing not available.
The most common cause of pump damage is the overheating of the pump through abrasive fluid. The metal debris in the oil is like sandpaper between the rotating parts. Due to the poor FLUID, higher friction results and the pump over-heats and is destroyed.
In rare cases, the pressure housing may crack, thus the pump leaks and fluid level drops dramatically. Also, the breaking off of the plugs from the pressure housing can cause this catastrophic loss of fluid and pump destruction.
Consequences of inadequate care and maintenance of your ABC system:
Dirty fluid will first slow the ABC hydraulic pump (plugged sieves). Many errors of the suspension result from the insufficient pump pressure. If the pump pressure of 200 Bar drops to about 160 Bar, the instrument panel will display in white/black: "ABC defective, please visit workshop".
If you then continue to drive the vehicle and the pump is working, the warning message will soon appear in red, (the pump pressure has dropped below 100 bar) and the ABC system goes into limp home mode. It closes the shut-off valves in the valve unit, so that the vehicle does not fall down. Your vehicle drives as if the shock absorber is defective.
With a red error message it is best to stop immediately and have your car transported to a service facility. If your ABC pump fails suddenly damage usually occurs throughout the system, as the fluid brings the chips with it. Continuing, the chips are distributed with the still small pressure in the system. That would be the worst thing that can happen. Your ABC suspension would then actually be a total loss. Mercedes Benz then recommends that all ABC suspension parts be replaced with new components. The ABC pump is a precision high pressure hydraulic pump that generates 200 bar, so everything must function precisely and with VERY low clearances. A metal chip left in the system is sufficient for the new ABC pump to be destroyed. Flushing the system in place brings no guarantee that it is clean, due to the branches (nooks and crannies??) throughout this complex system. A complete dis-assembly, flushing and cleaning by hand is the ONLY possible way to avoid future problems from such debris. Any other approach is Russian Roulette.
The cars we have serviced or repaired over the past years is proof of our approach. They continue to run well and do not return for ‘repairs’, only service.
Do you have questions, problems with your ABC suspension? Give us a call!
Phone : 03877-56 26 81 (Germany)
IF you are interested in seeing the components 'under repair', I strongly recommend going through the slide show of pictures at the bottom of their page.
Last edited by Gary Knox; 02-06-2014 at 08:05 AM.