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Discussion Starter · #1 ·
Forgive the long read, just want to provide as much info as possible. Fisher MM2, 8’ HD. 3 plug style, with 3 port isolation module. 6pin controller. 2 Stud headlights (if that matters).

Did a couple passes in my driveway yesterday morning, backed up, dropped the blade and I lost all directional controls all at once. So now its stuck down in my driveway. The motor is still activating when I hit the controller, and I’ve tried a second known working controller with no luck. Here’s what I’ve done and figured out diagnostic wise:

-ALL TRUCK SIDE WIRING/ELECTRONICS ARE NEW (aside from controller) Well a year old, but still pretty dang new.

-In September I replaced the fluid, pickup tube/filter, all the o-rings that come with that service kit, etc. It was working fine until this happened. The fluid that was in there before though was pretty brown and sludgy (ignored by previous owner). The first winter I had it the fluid actually froze up a couple times and the filter was pretty caked up when I finally swapped it out. So I’m not sure if some gunk or debris from before I serviced it could have gotten up inside the valve body and is now causing an issue several months later? Seems unlikely? There was a magnet in the bottom of the reservoir and I don't recall seeing any metal shavings on it, but I can't recall for certain.

-Reservoir is filled plenty of new, blue Fisher fluid. The pickup tube has a metal bracket holding it in place so I can’t imagine that fell off. And even if the filter fell off I believe the bottom of the pickup tube should be below the oil level.

-Tried a second, known working controller. Still no luck

-Headlights are all working fine.

-Power is indeed reaching the positive stud on the motor housing, and the motor is activating when pushing left, right, or up.

-Cleaned ground stud on motor housing and all connectors/washers/nuts with a wirebrush til everything looked new and shiny.

-There is continuity (with ~2 ohms) between the ground stud on the motor housing and the negative batt terminal.

-There is continuity (with zero resistance) between the ground terminals on all 3 directional solenoids and the ground stud on the motor housing.

-On each of the three directional solenoids there is continuity (~6.3 ohms resistance) between the positive and ground terminals.

- I suspected the plow-side wiring harness to have a short. However, my neighbor just so happened to have a new-in-package wiring harness and after installing it, still no change. Ground connections still good obviously.

-Using a test light grounded to the battery I have found that:

-S1 solenoid (Angles Down; drivers side position.) Only receives power when I press Down and will stay powered until I hit UP

-S2 solenoid (Angles plow Left; middle position) only receives power when I press the Left or Right button, which I was told by a tech at my local Fisher dealer is correct.

-S3 solenoid (Angles plow Right; passenger side) Is receiving power when I press the Left or Up button.

So at this point I THINK I can rule out an electrical issue, unless there’s something I’m missing? Unfortunately, in all my years of working fisher plows I’ve never had a serious hydraulic issue, aside from bad chunky fluid. So I’m kind of at a loss her of what to do next. Can anyone help me where to start on diagnosing the hydraulic system? I was thinking maybe pull out the solenoid cartridges and see how those look? But other than that I’ve got nothing.

For the sake of easy communication on here, I’ve attached pics of all the bit and bobs on the valve body that I have numbered arbitrarily. I figure we can refer to those numbers to avoid confusion. Thank you all in advance!
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Discussion Starter · #8 ·
Well, I just went out there but that thing did not want to budge much in either direction. I tightened it juuuust a c-hair but that took some force. Not sure if if something is preventing it from going down or the thread are just really gummed up.

Can I remove it to inspect or would that be opening a can of worms?
 

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Discussion Starter · #18 ·
The pick up /filter is in place and it’s full of fluid?

because now it doesn’t sound like it’s building any pressure.

But it is very rare for a pump to go bad.
If the pump was going bad when you drained out the fluid it should’ve looked grey and fill shavings. And the screen should’ve been full of the stuff too
Fluid is filled and clean and blue. I probed into the fill hole with a screwdriver and could feel what I'm pretty sure is the pickup tube, but I have yet to remove the reservoir at this point. When I serviced it back in September, I remember looking at the magnet specifically to see if there were any metal bits. Now I don't have a picture of it in my mind so I cant say 100%, but I don't recall being worried by anything I saw so I'm gonna say there weren't any metal shavings in there. The fluid iirc was a brownish color and very watery, reservoir O-ring was bad for who knows how long. The filter was clogged up with chunky sludge.

If I remove those two bolts that hold the motor on, does the motor just pull right up? Last time I did that was several years ago I can't remember what it looks like in there. I assume there's some sort of drive shaft going down into the pump, but don't know if you have to do anything special to pull it out from the pump?
 

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Discussion Starter · #20 ·
Yeah, the res is bolted from the bottom. Unfortunately the way that whole assembly sits in the frame, you have to remove all the hoses and remove the whole motor/res assembly just to get the res off. Not fun in a driveway in the winter. I suppose I could just drain the res and see if the fluid looks off.

The whole pump/motor assembly is on there snug, no play. I recall that when I had the res off in the fall, I didn't remove the pump to replace the o-ring for it that came with the service kit, but I checked to make sure the bolts that hold the pump itself in place were tightened to spec.

Now that I'm looking at some pics and jogging my memory, my thought is maybe for now I just remove those two long bolts at the top and I can slide the motor up and off and maybe get a look at whats going, though I am worried about snapping those bolts if they're rusted in there.
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Discussion Starter · #21 ·
for these pumps to go out is as common as the oil pump in your truck to go out.
I actually swung by my local fisher dealer yesterday to bounce some ideas off the service counter, one of the techs said he doesn't see it a lot but at a least a few a year. iirc he did have a recent case of some one losing all directional and it ended up being the pump.
 

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Discussion Starter · #26 · (Edited)
ok
Then why did you mess with everything else
And not pull the pump out?

When you hit float/ lower did that plow drop like a Stone?

because that quill should be easily adjustable and not frozen in place

good luck, you’re still fixing it outside
No difference if you’re messing with the valves or taking the reservoir off..
Well when I showed the techs my controller they all laughed and said thats where the safe money was, so I didn't want to go off half cocked digging into the hydraulics. Its pretty beat up and the rubber sheathing is missing from most the wire bundle. I wasn't able to get my hands on a second known working controller til this afternoon to eliminate that possibility, so idno I do think it was prudent of me to go through all the elec during that down time. At the time yesterday, I was also working with the assumption/HOPE that it was an electrical issue. 8 years plowing I feel like 99% of the issues I've had with these fishers has been electric. So I wanted to be thorough before getting into the hydro.

The last time I dropped the blade...I can't honestly recall if it dropped differently or harder than normal. It might have. Early AM, dozen other things on my mind wasn't really logging it in the ol brain. I agree messing with the hydraulics is gonna suck no matter what. But crawling on the ground and dropping the whole assembly is gonna suck extra.

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Discussion Starter · #28 ·
Even though that controller looks F’ed, from what you said about the coils, it sounds like it’s working ok

with the plow on the ground and the fluid full, usually you would be able to angle the plow if it was the pick up tube. Try that first. With the lift cylinder collapsed, there will be enough fluid in the tank that the pump should be able to reach even without the pick up tube
Yeah the controller ended up being fine, as confirmed with a 2nd controller. From comments others have made, the pump or shaft is looking more the culprit.

I should ask the group though, before I put all my chips on the pump, is it possible there is some debris clogged up in the valve body somewhere that would have stopped all fluid movement? Is it worth pulling cartridges or anything else out of the valve body to examine? Or is such a clog highly unlikely?
 

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Discussion Starter · #39 ·
Pretty sure that’s for your plow.
You're the man. Looking through this now seems like my first move is to pull the cartridge valves and inspect. The onto the relief valves.

My drop speed quill will probably need replacing too. Just watched a vid of guy putting a new one in and seeing how nice and gently his lowered mine was definitely dropping like a stone.
 
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