w163 ml270 powersteering mod? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 09-03-2010, 03:54 AM   #1 (permalink)
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w163 ml270 powersteering mod?

I have a ML270 with upgraded tyres, however the power steering is really hard, and giving me a unwanted manhandling challenge at times.

Are there any mods that can be done to the pump, or other components? Swap it out for other parts?

Suggestions are most welcome.
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Old 09-03-2010, 03:58 PM   #2 (permalink)
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I have an ml320 and I think the pumps are the same.

I will dig around in ALLDATA and see if there is a spring that can be shimmed in the flow/pressure relief regulator like on a saginaw pump. It may be a day or two before I get back to this though.
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Old 09-04-2010, 01:48 AM   #3 (permalink)
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Thanks! I hope you come up with something!
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Old 09-09-2010, 11:33 AM   #4 (permalink)
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haven't forgotten, just haven't gotten to it yet.
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Old 09-10-2010, 07:40 AM   #5 (permalink)
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I'm a patient man
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Old 09-13-2010, 02:28 AM   #6 (permalink)
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OK... I am making a few guesses here... but.

remove the cap and drain the reservoir... recommend vacuum bleeder for this.
remove the screw holding the reservoir on. (I think it should be just one)
While you have this off inspect the O-ring, mine was leaking which is why I know this part.

Here is where the guessing starts.

the "output" line (the one going to the rack) is connected to the side of the pump (Drivers side) and it threads into another hex-head fastener.
Remove the output hose.

I don't have a blowup of the pump but most flow regulators use a spring and a plate or ball. I believe this will be behind the larger hex-head.

hydraulic pumps are, by nature, positive displacement systems and so power steering systems are kind of the odd duck in how they operate. the pump pumps fluid with every rotation and the fluid is forced to exit the pump through a chamber with a spring operated relief valve. this chamber has a restrictor plate which governs flow from the pump. At idle (in a perfect world) the pump produces just enough flow to pass through the restrictor plate. as RPM increases flow tries to increase but it is easier for the fluid to exit through the relief valve than through the restrictor so the flow through the restrictor stays more or less constant regardless of RPM.

Some people "hotrod" their pumps by over-boring the restrictor (I did this) this is done to increase flow.

You need to increase pressure so the part you will be concerned with is the relief valve. You need it to require more pressure to operate the valve. This means that you either need to shim the spring, stretch the spring, or replace it with a stiffer dimensionally similar spring.

The large hex is probably the cover for the relief valve and also serves as the restrictor plate. Remove it carefully (there is probably a spring behind it). The restrictor probably looks like a hollow bolt. Behind it is the likely to be the face of the relief valve and behind that... the spring. The restrictors I have seen have their inlet through the sides and fluid can either exit through the output hose and into your steering system or if system pressure is too high (say at full lock) recirculate through the relief valve which serves to block off the back.

Once you have the spring out you will likely be able to decide what course is best. If you decide to shim it (like with a washer or two) make certain your shim does not completely prevent fluid from recirculating.

After this... if all has gone well. Re-assemble. replace O-rings with new as you go. and refill with Pentosin CHF11s, CHF7.1s or MB Genuine PS fluid

Good luck.
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Old 09-13-2010, 02:59 AM   #7 (permalink)
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Thanks man! I will definatly open it up and decide if this is possible, following your steps.
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