Yes, ABC IS just another hydraulic system, and doesn't need to be treated like rocket science or a black art.

The one thing that's unusual about it is the energy storage. The engine pump pressurizes the accumulators, and they store the hydraulic energy under high pressure. The strut valves OPEN to allow high pressure fluid into the struts (or out, as appropriate).

This is different to other hydraulic systems which have continuously circulating fluid at low pressure, and a valve is CLOSED to increase the resistance to flow, and hence build up a pressure against the pump's output. This means the pump's flow rate has to be high enough to meet every dynamic demand, which is rather high in the case of ABC.

Mercedes system means the pump can be much smaller and hence less of a drain on the engine than conventional systems. The accumulators are pressurized slowly and empty quickly. That's why accumulators are key to ABC operation.

Otherwise its just industry-standard hydraulics, with lots of SAE 100R2AT 3/8" two-wire braid flexible hoses everywhere. Gates and Parker are the best known makes.

Getting air out of the system is no big deal. I'm sure a rodeo is the best way to do that, as its the only way to exercise the struts to the end of their travel - level control doesn't do that - however just driving around seems to do the job fine. However, if the pump is empty, you DO have to bleed it. That's essential, but no problem. I just removed the poly-V belt and spun the pump round until it went solid.

Rodeo is a tough test though. There are lots of accounts of working systems developing faults after a rodeo, through stress testing if you like. One of the features of rodeo is that it doesn't give the pump time to refill the accumulators - the pump is worked continuously at max flow, and the pressure inevitably drops. Its supposed to do that - its not a fault. The pressure drop is a performance measure for the pump.

Nick

 

Thanks again Nick:

I'm sure there's still oil in the pump, but the hose has been off for several days now and I siphoned almost all the oil out of the reservoir. There's still maybe 5 mm of oil left at the bottom of the tank. The last time the engine turned over, there were several inches of oil in the tank. Obviously, I'll fill it with new Pentosin when the new fluid arrives.

My concern is: Did I loose oil out of the pump with the hose being off for several days? I didn't notice much oil coming out of the pump when I pulled the hose... but really wasn't paying attention. If I understand correctly, it's a radial pump so most of the oil can't leak out. It has to be pumped out with a dry reservoir??? In my case, that didn't/couldn't happen. There was always plenty of oil in the tank when the motor was last running.

My plan is to install the new hose on the pump and leave the bottom connection open, crank the engine (bump the starter), and check for oil coming out the open end. That way I don't have to remove the belt for a hand crank. And, hopefully will get most of the air out of the new hose.

Thoughts???

Best Regards....Mark

 

"...crank the engine (bump the starter)..."

Be ready for a surprise! Remember that when you engage the starter, the computer continues to spin the starter until the engine starts...

This could get messy! I think that I would either take the belt off, or just hook everything up and drive it. But then, I am a lowlife with Airmatic, and know very little about ABC.

 

Good point....Thanks

 

I doubt you lost all fluid and can just refill and go

 

Thanks all for the advice:

Hose and fluid arrived today, a day early. Everything went back on pretty smooth.

I primed the pump by loosening the serpentine belt tensioner and turning the pump with a star socket wrench by hand with the belt in place. That way I didn't have to take the belt off.

When several squirts of Pentosin came out of the open bottom connection, I finished connecting the hose.

Drove the car a little bit and everything worked fine... a happy ending... until next time...

Anybody have an opinion on the service life of the accumulators? My hose blew at 60K miles and guess the accumulators might be due. The car doesn't ride harsh or anything.

Regards.... Mark

 

PS... In case it helps someone else out, here's my post on another forum with some description of how to replace the high pressure hose... #71

https://mbworld.org/forums/cl-class-...ectancy-3.html

Regards... Mark

 

Accumulators can go anytime , some last 120k or more miles, some fail at 40k

 

Thanks Tusabes:

The accumulators, or Nitrogen Bombs, as I like to call them (because they look like the bombs in Spy vs Spy, a la Mad Magazine), were gone on my Ferrari at 18K, but they were 19 years old. The MB's are only 8 years old... hope it's age not mileage.... I have 60K on the MB....

I've heard you'll feel some pulsating in the ABC if the accumulators go in the MB.... I don't have that....

IIRC, on the MB, you can also push on the fender, and if it's not hard, the accumulator's are bad...... or is it vice versa???

You can also take them off, the accumulators, and check if the membrane is still intact. (I'd just as well just replace them as check them in that manner...so that's not a good option...)

Thoughts???

Just me being ****, but I want to eliminate all causes of this hose burst... And you're several days from going anywhere if it happens to you....a hose burst that is....

Regards....Mark

 

Sorry....... one more thing:

There are two marks on the ABC dipstick; the highest one is with engine off and the lowest with the engine on. My German's not so good (this stick is written in German)... but the level drops with the engine running...

Anyway, I'm guessing the drop in fluid level (maybe a 1/2 liter), is due to the compression of the nitrogen bombs (accumulators).... Just a WAG...

Can one conclude, if the ABC level drops, your accumulators are okay?

Maybe not.....Just thought I'd throw this out there.......

Regards....Mark

(Again, sorry. I'm a day ahead of my parts delivery.... so I've got time to waste asking stuff probably no one else thinks about....)

 

That's exactly how it works.

You have to allow some for pressurizing and de-pressurizing, but in simple terms if you have the static level at the upper marks, and it drops down to the lower level when running, that's a good indicator that the accumulators are OK.

If the level changes by either more or less than that, it indicates you have a bad accumulator or two.

They're relatively quick, easy and inexpensive easy to change. Relative by other Mercedes ABC standards.

Nick

 

Anybody have a link or knows how to Repair the High pressure line. My power steering high pressure line that runs from steering pump to a dead end under the steering column. The rubber/fabric hose come out of the metal adapter. Is there a way to connected it back to gather. Replacing the hose is $250 cheapest I found, how ever to do it you got lift engine to get the line off the power steering and seems like a big P.I.T. A.

Thanks for advise i know this post old

 

Have you tried reading the ABC suspension thread:

https://mbworld.org/forums/m275-v12-...on-thread.html

Nick

 

Amazing! Thank you so!