ChrisCL600

Hi everyone, I am a little stumped on an ABC issue i seem to have self inflicted somehow. I have installed a new pump and am immediately getting the same pump noise i encountered on the previous pump(no ABC warnings as yet). I have tried to capture all of the details below on build up to my current issue. Any help would be greatly appreciated:

1. After replacing my radiator due to a leak, i noticed that i also had a small hydraulic leak from the high pressure lines coming from the pump(i had no noises or ABC issues at that point and although fluid was low, it was still clearly visible on the dipstick)
2. I removed the affected lines and had them rebuilt
3. I reinstalled the lines attempting to keep everything as clean as possible, pressurized the system and performed a rodeo. Note when replacing the line, i was not able to re-install one of the line routing securing bolts to the side of the engine and so was sitting slightly low, barely touching the subframe(I do not feel any vibration on subframe)
4. I did not hear any unusual noises at that time as the car door was open. The next day on starting the car and driving to work, i immediately noticed a distinctive 'hum' that increased with revs(constant). I cannot hear with the window even slightly open(resonator deleted ). The noise is gone at ~2k revs however i believe only because drowned out by the motor/road noise.
5. Drove the car for a few days as i was searching through the forums and after ~2 weeks i got my 1st low pressure warning followed by red warning. Noise was consistent during this time ie did not get any worse before the 1st warning.
6. I saw pump pressure was now drifting from 180 bar on engine start and would drop to ~100 bar, increase on rev and then would gradually decrease. Assume i had somehow killed the pump somehow on replacing the lines so ordered new pump/filter
7. Installed new pump/filter, performed slight flush(couple of liters) and saw good pressure/rodeo completed w/no issues however when closing car door, i can still hear the whine!!
8. Pressure is still good and have no symptoms other than the noise in the cabin however obviously concerned that i have not fixed an underlying issue and my new pump will fail again in short order!

There are no leaks and i never allowed the pump to run out of fluid. The previous pump was ~12 months old when it mysteriously started to have issues post my line replacement. The lines i replaced showed some rubbing hence the fail.
I have not noticed any strange noises coming from the pulse damper and i get the whine/hum when stationary.

Thanks in advance!

Fried Chicken

You answered your own question:
Just because you don't hear it at the contact point, doesn't mean it's not making noise somewhere else.

Easy solution: add a piece of rubber or something between the subframe and the line (cut a larger hose, cut it apart lengthwise, slip it over where it's hitting the subframe, and zip tie it on). That'll either partially or completely remove the noise if it's the issue. Another solution: route the line properly. You don't want the liens touching, the vibrations can lead to failure.

That's my guess, and where I would start, but I could be wrong.

ChrisCL600

Thanks for the quick reply! When installing the line and noticing that there was some contact, i did just as you stated...however noticed that my attempt to dampen w/hose had become loose when installing the replacement pump so did not bother to replace again(did not detect any difference in sound with/without the additional hose in place). With the engine running i did get under the car and place the stethoscope to the subframe at that point and did not hear anything unusual however wanted to document this as a difference in my original post.

Fried Chicken

Which line exactly did you replace?

ChrisCL600

Hi, I had both high pressure hoses with banjo fittings rebuilt by Hydraulic shop

ChrisCL600

Bump

Fried Chicken

Possibly the banjo fittings causing noise, idk.

Benz0matic

Did you get the air out of the lines?

ChrisCL600

Yes, I believe all air is removed. I completed several rodeos and do not see any air bubbles in the fluid with car running.
I monitired the pump pressures on the DAS all the way to work this morning and pressures stable at 175-180 Bar with occasional dips to 160 when I hit a bump then very quickly recover.

Fried Chicken

I'm 90% sure one of your ABC lines is touching the body of the car. You might want to check on your pulsation damper to verify that's not it, but since it wasn't a problem before, and especially because you're saying you had the lines rebuild rather than genuine OEM, I'm 90% sure a line is touching something it shouldn't somewhere.

You should check this for two reasons, 1. to get rid of the noise, 2. because touching hydraulic lines will wear eachother out and cause premature failure.

Fried Chicken

I just got done fixing my ABC system, details here:
https://mbworld.org/forums/s-class-w...ne-popped.html

ChrisCL600

Hi, sorry to read about your ABC woes over the last week. Good news all is sorted.
Yes, i was planning to lift my engine off the subframe slightly this weekend to see if this would remove the noise if the root cause was rubbing on the frame. I am starting to second guess myself that the pump/system has an issue as the ABC pressures are rock solid and i guess my last pump may have died for another reason..... So plan to remove the serp belt and run for a few seconds just make sure the noise isnt coming from the engine/tranny.

Fried Chicken

Why don't you just double check the hoses that you had fixed and swapped out? See if it's touching the body in a way it shouldn't.

Benz0matic

I meant purging the air out of the lines via the bleed screws(# 56) in the diagram...
http://www.benzworld.org/forums/atta...-abc-bleed.pdf