carbizindio

The suspension pulsation damper will cause a humming / buzzing noise when not working correctly.

See TSB Topic number LI32.50-P-048280 for more detailed information.



Not every thing I do is according to the strict guidelines of WIS, so use my directions at your own risk.

Jack up front end. Find the 2 bleed screws on the LF and RF next to the torque strut bushing and bleed the system. Make sure you have the car secure because you will lose all suspension pressure after this is done.





Remove the pulsation damper. You will need a 24MM wrench for this, because of how the threads are welded to the unit you can't fit the wrench in every position. Maybe you can take this off with a oil filter remover?



This is a good time to change your filter for the suspension.



The top is held on by a hook, remove by pressing down on the spring.


My fluid was black so I pumped out what was in the res. try to be as clean as you can be.


Fill up res to the engine off min/max, install filter.

I started the car and set it to normal height, check fluid level at engine on min/max. Raise up then normal 15 times if any major components were replaced while checking fluid level only when set in the normal ride height level. If you hear a hissing noise in the area where you installed the pulsation damper or in the rear of your car then shut it off and bleed at the same bleed screws.

I had the hissing noise so I had to bleed the system 5 times. I had no luck getting rid of the noise. I ran the rodeo and dynamic test along with testing the pump and other components and had no codes after I was finished.



At the end the main problem of the humming noise is now gone.

carbizindio

sorry for the double post, user error

05CL55

Hey so did that hissing noise go away? Mine is hissing too, and I'm wondering if its the valve as well as the damper that needs replacement. Sometimes when the damper goes bad, the contaminates damage the valve too. Let me know if yours is still hissing, or if the ride improved when you replaced the damper.

carbizindio

The original loud humming noise made by the bad damper is fixed. I'm not sure if I had the hissing noise before because the humming was so loud. I still have the hissing noise after 100miles on the new damper. I need to bleed the entire system front and rear before considering the pressure supply valve unit / Ride control solenoid valve not working correctly.

carbizindio

if your going to replace the valve I would say replace the damper also, its not a whole lot of money and its a huge improvement on the internals of the damper VS. the original damper.

tusabes

what does the damper do besides the buzzing? does the ABC still work with a bad pulsATION damper?

05CL55

carbiz, does yours still hiss?

First I changed the pulsation damper (hissing started), then the other day I did the front valve block, front pressure reservoir, filter, and mine still hisses after bleeding...

paultyk

Have you replaced the fluid? You should replace fluid while pouring fresh one return should go to separate container until fresh one comes out. While doing rodeo, that way all old fluid will go out, and that helped me.

paultyk

I did it with help of another person otherwise could be messy.

05CL55

Yes, fluid changed, and was SUPER messy

carbizindio

I still have the hiss. alldata said its a very bad noise and should not be driven. I've ran 2 rodeo's and a few thousand miles with no issues yet. I just think its a matter of how many bleeds front and rear are you willing to do, its a real pain if you dont have a proper lift.

MB-Dude

Paultyk - When you changed the fluid, what do estimate the flow rate of the ABC Pump was? In other words, how fast did you add ABC fluid to the reservoir? A quart a minute? A quart every 15 seconds? I'm trying to gauge how much old ABC Fluid will exit the system, especially during 'rodeo'. Thanks.
Cheers,
Jeff

paultyk

I would say a quart every 20 seconds, at the same time I replaced the pump too, I had enough fluid to add so I stopped when fresh one came out. I stopped rodeo when fresh one came out, nice and clean. And that also stopped lowering itself overnight when fluid flashed. It was quite easy because I had a help, I controlled fluid flow he operated functions with scanner.

Jud Chapin

Great post. How much fluid comes out during the bleeding?

paultyk

I have replaced another dumper today for a friend. The easiest way I think is to check that pressure in the system is 0 using diagnostic scanner. Then take dumper off of valve unit slowly and only minimal fluid loss will appear. Then put new one back. Add fluid between lower and upper mark on dipstick and run rodeo to the point no bubbles appear on dipstick. Make sure fluid level is correct. No noise and no other problems. Nice and clean. But we did not change the fluid.

holycowe

Just did the abc fluid flush today with a friend at his shop.
Followed exactly the steps on another thread under s55 forum (s55 diagnosed today) . VERY ez job, did not need to connect to a computer system.
Total 10 liters should be more than enough for the abc system (very clear fluid come out). Flow rate about 45 sec per liter.

MB-Dude

Congratulations on the successful ABC flush! Thanks for the flow rate info, as well.
Cheers,
Jeff

carbizindio

I would very much recommend the flush. I never flushed the system but I changed the fluid for the 2nd time out of the Res. It was almost as black as the first change.

steadystud

10 Liters ???? for the ABC flush ??????

carbizindio

I think that number comes down to how good you want the exiting fluid to come out looking like. This number will change depending on your current fluid condition and how picky you are on the end result color. I'm not sure if it was mentioned or not but you should pump out the old fluid in the res and refill before starting the flush in order to conserve the amount of new fluid.

MB-Dude

In my research of the ABC Fluid Flush, I asked my local MB Dealer what their thoughts were. Surprisingly (perhaps not), they also recommended 10 liters of fluid. Their work flow is identical to all discussed in this thread (remove ABC return line, drain/refill ABC res., run 'rodeo', etc.); just they would use 10 liters of fluid. Personally though, I would be shocked if anyone - even the dealer - would seriously require more than 5 liters, especially if the fluid is any reasonable color. If the fluid is truly black, then maybe 10 liters should be considered. But if that is the case, I'd be looking for something that is causing the discoloration. FWIW.
Cheers,
Jeff

Oxygen

Fantastic write up! Thanks so much.

Few questions - did you notice the humming was especially loud when in reverse gear? Did the ride quality improve with the new bumper?

carbizindio

I can feel a very slight change in higher speed handling, but the major plus is not having that loud humming noise. The humming noise was rpm specific, I didn't notice a difference with reverse vs drive.

benz_addict

Excellent! Thank you for the pictures!

steadystud

Hi carbizindio,

I cannot see the pics. SO would you please e,mail them to me @ steadystud73@yahoo.com ???? Also I see that my car has slower speed... due to this.. Is this because the Engine mounts (MB claims to be so) are bad?? would that cause teh humming/light groaning noise??

Thanx..