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2001 ML230 - As of 11/1/10 152000 miles
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Discussion Starter · #1 ·
My wife's power steering pump started whining really bad Saturday afternoon. I mean it went from no whine to whining really loudly between the time I parked it and walked in Home Depot to when I started and turned to pull out of the parking lot.

I did some research on the site and found the issue with the reservoir. Lucky I searched, I was this "" close to buying a new pump. Anyway I followed the directions and installed and bled the system in about 30 minutes. It is truly easy modification.

I also decided to dissect the old reservoir and found the issue amoung others. When I removed the old fluid I found it to be extremely dirty and dark. It was not burnt, just dirty.

I cut the reservoir in half with a air powered body saw. I was expecting to find some kind of valve from what I read on here. There was no valve, but a large filter framed with plastic. The filter media was torn which I believe was causing the pump cavitation. I also think when the media tore it released the crap inside the filter and let it flow through the system.

The filter media is VERY fragile, to the point of just pressing it with my finger would tear it. So I can see if air is introduced into the reservoir, it could possibly be violent enough to tear the media.

Anyway, the new reservoir fixed the whining to my surprise, especially because how much noise the pump was making.

Thanks again for the site and the tons of information available here!!!
 

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ML320 2002
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1,668 Posts
Congrats and welcome to the DIY'ers club! You will be the first member on this forum if you post a picture of that darn reservoir filter!
 

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2001 ML230 - As of 11/1/10 152000 miles
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2 Posts
Discussion Starter · #3 ·
Well, not the greatest pictures. I would have been a little kinder and gentler if I had plan on photographing them. Most of the filter media was destroyed by me.

This one is the front of the reservoir. The yellow plastic was the filter framing. This side of the filter media looked to be intact. You can see the media at the lower right. The stuff was VERY fragile. Just the touch of my finger tore the filter.


The is the back side of the filter. The area with the hole in the lower right is the section that was torn. It basically looked like an open door with only the right side still intact. The rest of the filter looked intact, but it was hard to tell since I made a cut all the way around the housing. All the black chunks of plastic was from cutting the housing.

 

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ML320 2002
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1,668 Posts
Thank you! I think pictures are enough to tell cause of the problem. The ps fluid return hole (higher one) is directly facing the filter membrane. When high pressured air rushes out of the p/s pump, it blows the membrane into pieces. One side blown filter causes unidirectional filling into the cavity which ends up causing quite a bit of noise. Designers didn't think about replacement procedures.
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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7,035 Posts
Yep - spot on description, and the reason the correct bleeding procedure needs to be followed on the reservoir replacement.

It's the pesky power steering hoses and connections need to be checked by VIN with the dealer to see if any outstanding recalls. Poor hoses and hose connections, and/or seeping o-ring are the major sources of air introduced into the system to begin with.

Good work - keep the faith !
 

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2001 ML430 Sport bought in very nice shape despite 156K miles in August 2010
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540 Posts
Nice info - many thanks!

Power steering on my ML is perfect, if think. Is does moan like a calf at full lock [only]. I've put that down to bleeding pressure with the rack at full lock. Is that normal?
 

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ML 230 The real Benz World Junior, GMC Sierra 400hp Nitro, Opel Commodore B Coupe 1001hp.
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132 Posts
Ml230 Integrated pump and reservoir.

Sorry to bring this up again.

Standard whining and irratic steering responce....

My reservoir and pump seems to be integrated without the possibility to take them appart.

How did you do this? I can't see how t may be done. Also the local mechanic said thet the 230 had a different pump/reservoir setup then the 320 and upwards.
 

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2000 ML430, 2000 C280
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920 Posts
For those who do not want to do the job themselves:

I just had my power steering reservoir replaced for about US$150 at an independent shop. They did a great job in getting all the air out, and now my power steering is very quiet. This is not an expensive repair.

DelJ





My wife's power steering pump started whining really bad Saturday afternoon. I mean it went from no whine to whining really loudly between the time I parked it and walked in Home Depot to when I started and turned to pull out of the parking lot.

I did some research on the site and found the issue with the reservoir. Lucky I searched, I was this "" close to buying a new pump. Anyway I followed the directions and installed and bled the system in about 30 minutes. It is truly easy modification.

..
 

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2001 ML430 Sport bought in very nice shape despite 156K miles in August 2010
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540 Posts
I remember reading that there was a visual check of the ps fluid circulation that confirmed a failed revervoir filter. I had a nasty noise this morning that seemed to be ps-related. Checked the fluid level, which was just a tad low. Topped it up with MB fluid. I now see turbulent fluid inflow at the top of the reservior, but no signs of air.

Anyone recall what the visual signs of a failed reservoir filter when looking at the fluid flow in theneck of the reservoir are.....???
 

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2001 ML430 Sport bought in very nice shape despite 156K miles in August 2010
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540 Posts
Look at the fluid surface in the reservoir.
It should be calm.
If the surface is turbulent, the fine gauze membrane in the reservoir is damaged, and the pump will ingest air with the turbulent/aerated fluid.
Another reservoir is the only fix.
Yep, that was the bit I has remembered reading. On this basis, my turbulent fluid, regardless of any sign of air entrainment, is proof of failed filter media. I'm ordering a new reservoir today. Thats a great writeup, dirtdodger, especially for a banana bender :)
Cheers,
Tony K [expat Aussie]
 

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1999 ML320
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126 Posts
A FAULTY PS RESERVOIR CAN RESULT FROM ANOTHER PROBLEM, AND MAY CAUSE OTHER PROBLEMS!

Thanks for the great pictures - worth a thousand words!

Seems like any failed hose, pump, or ps fluid leakage needs to consider a replacement reservoir just to prevent other issues later.

Following is my recent post from another related thread on power steering problems; http://www.benzworld.org/forums/w163-m-class/1351110-help-replacing-power-steering-pump.html

The photos of the cut open reservoir make sense of just about all the power steering problems everyone is having. It seems very likely that any air circulating (and therefore causing pulsation) through the circuit could potentially break a delicate screen. Any broken screen segments can cause fluid flow problems and potential blockage at the reservoir outlet to the pump, and hence backup problems for the return flow too. A pump starved for fluid due to a restricted inlet can cause the whining (pump cavitation) many people are experiencing. The next obvious question becomes; What damage could screen segments/particles cause to the downstream pump, rack and pinion, and cooler if they manage to get around? Seems like the faulty MB hose connection (a problem recognized by MB in their recall) may snowball into plenty more problems for many ML owners!

I did not read anywhere what this delicate reservoir screen material is fabricated from. "Fine gauze" was mentioned by somebody. If it is metal screen, pieces and smaller particles does not seem likely. Does anyone know what the material is, and if it is likely to break into smaller particles from failure?

Even when the ps fluid return hose is replaced in a recall before failure, if the bleeding procedure is not done exactly as 43sqd has been emphasizing, it seems an owner could potentially have any of these other problems later - as I have experienced.

Does the reservoir cap create a seal, or can a restricted reservoir outlet (the supply to the ps pump) cause return fluid to leak out from the top of the reservoir?

Thanks,

John
 

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Jusr removed the reservoir from my brother's 2000 ml. I cut it open and took a few pics. Will post on Monday. His screen was blown out as well, causing noise.
 

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You can see that the screen was blown out of the reservoir in my brother's 2000 ML320. I guess the dealership didn't know what they were doing...
 
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