YM226D Power Steering Rebuild

[Smoody]

Hi Everyone, Hope you all had a Merry Christmas.

I have a project I need to do on the Yanmar, my power steering has been leaking fluid for awhile now and is getting worse. It drips and also shoots hot fluid into the air when I turn a certain way, there is a small pin hole on the top of the valve where this happens.

The markings on the cylinder are, main housing "PH5001" and on the side "FM5004". I was hoping someone has tackled this project or knows what type of power steering unit this is, Yanmar or After Market? I just probably need seals/orings for it, hope they are available.

Any help identifying this is appreciated. I attached pictures for reference.

I did come across this old thread here back from 2006, never really went anywhere with much detail.
http://www.tractorbynet.com/forums/yanmar/74778-ym226d-pwer-steering-unit.html

Thanks

 

[careyo63]

If the fluid is coming out of the pin hole "were it's nice and clean" that looks to be a vent hole. Which in my unexpert opinion is a cyl leak. and prob just a bad Seal. I can't see why a Hyd.Shop can't go through it. Doesn't look like there's much to it.

 

[winston1]

Might be the same unit as the 186 shown in this thread. http://www.tractorbynet.com/forums/yanmar/218151-anyone-have-pics-power-assisted.html

 

[Smoody]

I spoke to a yanmar parts dealer and was told there are no factory yanmar power steering units, even the US models were equipped with after market. But I am not so sure that is a true statement, I cleaned it up a bit and found a tag on the back of the unit, its facing the tractor so it would need to be removed to see the serial number on it, but it does appear to be a yanmar model. I managed to get a pic best i could, don't have time to remove the cylinder today.

Was hoping to fix it myself but may just take it to a hydraulic shop if no one has any advice / experience fixing one of these.

 

[Smoody]

Winston, those diagrams do look just like my unit. i will look through that thread, thanks.

 

[careyo63]

Look at the bottom right PH5074-1 seal kit. Someone should have it. I can't find it so IMO. Hyd shop.

 

[California]

When I bought the second YM186D a few months ago I had the same problem on the same PS unit. (Maybe the 226 kit has a longer linkage or other external attachment differences but the cylinder is the same.) The manual in the thread linked by Winston covers this system. My research indicated that old threads here are the only documentation available anywhere aside from that original manual, and that the supplier of the kit disappeared decades ago.

The problem, documented in an old thread, is that the control piston driven by linkage from the steering wheel has that vent to let air escape beyond the piston. But the O-ring sealing the control piston wears out and lets fluid leak to the atmosphere side of the piston. This fluid squirts out the tiny vent hole when you turn right (left??) and the piston moves forward.

One of the old threads here said it is simple but time-consuming to remove the kit and replace that o-ring. The process is documented in that manual.

However I looked mine over and the project looks more difficult than I expected. You need to somehow grasp the delicate aluminum body casting while applying 100 ?? ft lbs of torque to the big nut at the back end of the primary piston, before you can remove the little control piston that is the problem. Also on mine I was unable to unscrew the steering link at the front end of the cylinder casting, or the rusted length-adjustment threads at the back end of the linkage, back by the steering box. I decided to put the project aside until I had plenty of time to approach the project thoughtfully. A year has passed ... . The fundamental problem is that the aluminum body casting is irreplaceable and looks delicate, and I don't see how to hold down that odd shape to unscrew components from it.

Another issue the manual describes as critical is that the balance of steer left / steer right pressure is calibrated during factory assembly and requires special equipment. (that probably doesn't exist today). So don't take apart the component containing the balancing springs! O-ring replacement can be completed without getting into this. We just need to remain aware that that sub-component is not to be disassembled.

I gave up and covered the hole with a radiator hose clamp to direct the fluid downward as a dribble, instead of squirting upward into a big puddle in the loader chassis and drenching the side of the hood.

I'll replace the O-ring when I get around to tearing down the kit - probably after someone else describes how they did it.


Anyhow power steering sure is nice. I didn't realize what I was missing!

 

[Smoody]

Well that pretty much explained it very well and sounds to be a pain in the you know what.

So I am clear as to what you are saying do not take apart, can you reference it from the diagram in the other thread? Also which oring are you referring? #11?

maybe you are referring to not taking the cover "FM5004" off, from my attached picture above?

lastly, any idea what size that o-ring is?

thanks again

 

[California]

Just from memory -

There are two hydraulic pistons, side by side. The large one provides force to steer left or right. For the tiny one, its piston is pulled forward or back by the steering linkage as you turn the steering wheel. As this little piston moves, it uncovers a fluid passage to the front or back side of the big steering piston. (The small piston functions about the same as the control valve on your loader).

It is the piston O-ring in this smaller cylinder that wears out and passes fluid to beyond the piston, down by that air vent. To replace this worn O-ring, the whole PS assembly has to be removed from the tractor and clamped into some sort of fixture. Then the end cap of the larger cylinder is in the way of removing the smaller cylinder's end cap so the larger cap has to be unscrewed and removed.

As I recall the caibrated component is in the end cap assembly of the smaller cylinder. To replace the leaky piston O-ring you remove that end cap assembly, piston rod, and piston, as a single unit - just don't disassemble the end cap assembly.

The shop manual posted by Winston over in the other thread covers all this, hopefully more clearly than this stuff I'm writing from memory.

 

[clemsonfor]

Maybe take it to a real Hydraulics shop that does this stuff for a living and tell them about the calibrating piston or whatever. They probably know exactly what it is and how to fix the whole thing. Yanmar cant be the only thing that has used this setup. I would find it really strange that yanmar R&D a whole new system 30 years ago that has never been used in a similar capacity on any other hydraulic componet before or since.

I know we like to do things our selves for the satisfaction and know how and to SAVE money but when your talking about irreplaceable parts and castings other than salvage that may or may not exist today, why not take it to an expert and see what they would guess the cost to rebuild to be?

I think i would take it somewhere at least have them look at it and estimate a cost for me based opon packing and oring replacement