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Power Steering Noise 99 ML320

11K views 22 replies 11 participants last post by  art_arev 
#1 · (Edited)
My 99 ML320 has developed a whine at idle that increase with RPM's. The steering seems to work fine for now, its just the noise that is driving me crazy.

It's hard to pinpoint exactly where the noise is coming from but I think its the power steering pump because when I put my hand on it I can feel the vibrations. The noise is kind of a high pitched howl. The pitch and intensity increases with the RPM's.

I live in the Boston area and have driven the truck here since it was new.

Any thoughts on what this could be and how to troubleshoot it?
 
#4 ·
Yes you probably have a leak. But in my experience 30 years of auto repair manager/ ASE Tech. When you have a noise as loud as you describe it may require replacing the power steering pump with a good remanufactured pump (NAPA) rock auto dot com and a new reservoir with O ring.

The reason I say new reservoir is that it contains a filter (screen) and based on the age of your ML it would be a prudent idea to get a new reservoir (Carquest/ World PAC) about $30.00 with O ring.

But the power steering fluid you will need to get from a MB Dealership. I have not been able to locate it outside the Dealership. Not even Pentosin!

https://www.rockauto.com/m/mobilecatalog.php




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#5 ·
It is good to hear you have all of that experience. The inpunt techs with experience have is very helpful to members that need advice.

If a pump is needed the brands like Beck/Arnley, A1 Cardone and all of the big box store pumps do not come with the aluminum pulley. It is virtually impossible to to press the old pulley off of the orginal pump without ruining it. So getting a good rebuilt ZF pump with the pulley on it is the way to go. Looking at Rock Auto they do sell a Cardone with a pulley and also a Luk.(I would go with the Luk)
As far as the reservoir many members have tried and failed with aftermarket parts. The reservoir and the o-ring have to be genuine MB or it will leak again in short order.

I still suggest marc00 checks the level of fluid and if needed add the correct type of fluid. If it does not work it is still a lot cheaper than putting a new pump on.
 
#6 · (Edited)
Hey guys. Thanks for responding. The pump is not leaking. I should have mentioned that in my original post.

I have not been using MB fluid which may be the cause of the problem. Ill be sure to use some with the repair.

Ive seen some old threads and even some instructions from 43sqrd on how to replace the reservoir. Is that no longer recommended?
 
#8 ·
Thanks, Ill keep that in mind if it needs to be replaced. The steering works fine right now its just the howling noise thats driving me crazy so Id like to troubleshoot it a bit more before investing in a new pump and reservoir.

Is there a test or tests I can do to determine whether the pump needs to be replaced?
 
#9 ·
Start with draining the reservoir, and bleeding and filling the system accordingly. (Jack up front two wheels after draining fluid, fill with MB spec fluid, turn steering wheel full left to right 30 times to get air out of system (this will be harder as it goes), check level again and fill to mark accordingly to lower mark) and see if the noise is still there.

If there's air in the system (that crazy noise you hear), it's tough as hell to get it out.
 
#17 ·
If you need one quickly many of the big box auto parts stores carry the Dayco or Gates replacement. The down side is that the plastic cover from the original does not fit.

I have been running a Dayco for a couple of years now no problems at all. Also do not over tighten the the bolt (which is so long the fan may have to come out). It is going into aluminum
and a couple of times members have broken the bolt. I do not have the torque spec with right now, but it is much lower than you would expect.
 
#18 ·
Make sure its the P/S pump and not the A/C pulley. Get a short belt and bypass the P/S unit...someone here may be able to tell you the size. If not, you can run a string around where the belt would run and measure it, belt's are sold by sizes so if you have the size you can get whatever size you want.
 
#19 ·
Thanks, great idea. I will try that if I can figure out the size.

I will add that I do not feel any play or resistance in any of the pulleys when I turn them by hand. The reason I think the noise is coming from the PS pump is that I can 'feel' the noise when I put my hand on it while the engine is running. does the pump itself typically make a noise before it fails or does the noise typically come from the pulley?

Still have not tried bleeding air from the PS system. Will try that after fixing the idler pulley and report back.
 
#20 ·
marco, if you have replaced the pulley and there is still a PS noise, the smart thing to do is replace the reservoir and O-ring first and then properly bleed the system.

The reason you feel the noise in the pump is because the fluid is continually flowing through the PS Pump. If the screen inside the reservoir is faulty or air is entering the system, you will get noise. But 99% of the time it is the O-ring or reservoir.

Do not buy an aftermarket O-ring or reservoir, buy from the dealer.
 

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#21 ·
This same thing happened to my 2003. I replaced the reservoir with the o-ring and it went away.

Be sure to bleed the system properly after adding new fluid or you will be adding a rack to the tab.
 
#22 ·
43sqd, Thaks very much for your post. I did replace the idler pulley and I also bled the PS fluid according to the instructions you attached but the noise did not go away. When I had the fluid out I could see the screen at the back of the reservoir and it was indeed faulty. It looks like it had basically disintegrated on the left side. I'm not sure why that would cause the the noise but it clearly needs to be replaced.

I'll pick up the reservoir from the dealer but where is the O-Ring? I assume both should be replaced. Is it really of the sealing-ring in your diagram (Part 30b)?
 
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