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MM2 Intermittent Hydraulic Problem

Discussion in 'Fisher Engineering Discussion' started by dmax 2500hd, Dec 24, 2008.

  1. dmax 2500hd

    dmax 2500hd Junior Member
    Messages: 18

    :confused:Hello everyone-

    I have a Fisher MM2, 8'HD straight blade plow with InstaAct Hydraulics. Occasionally, the plow does not raise. The motor relay clicks, and the pump engages, but sounds like it is frozen. The only angle function that works is angle right, even when I hit angle left. If I drop the blade and run it into a snowbank, or I back up with the blade lowered, it will start working again. The problem is intermittent, although it is happening more often...

    Recent service and part replacement list as follows:

    -Fluid changed this season..New Fisher Blue fluid.
    -New valve in position # 3 ,(figuring that valve was not shifting)
    -New wire harness from plow side to vehicle control...nothing replaced on truck side.
    -No metal shavings in pump or in valve positions #2 or #3 (used magnet to check...)
    -New coil..
    -Poppet valves appear to be working

    Please help guys, I'm losing my mind with this...I have been back to have it serviced three times now, with no luck...Just a grocery list of new parts that aren't fixing the problem....
    Thanks in advance.

  2. We have several of these as well, 3 plug systems, all Insta Acts 8's or 8.5's This problem is driving us crazy as it is intermittent and happens during the storm. It is very difficult to duplicate. We have done all of the above as well but have done the truck side harness too. These things act really crazy with bad grounds. The only thing we have left to replace in the joystick/fishstick but would rather know what the problem is before throwing more parts at it. Anyone!!!
  3. bula_1984

    bula_1984 Member
    Messages: 45

    If the plow has a digital controler check the in cab plug. Otherwise check all the grounds and conections on the pump and relays. sounds to me that when you have vibration that is when it acts up. could be a loose conectoin or a loose fuse. Hope this helps
  4. dmax 2500hd

    dmax 2500hd Junior Member
    Messages: 18

    Took it to yet another Plow Repair shop today, and they could not get it to duplicate the condition. They said that they tightened up a few connections that were loose, maybe that is the problem? The only thing that I can see that hasn't been replaced is the Fishstick-:(

    Still looking to hear if you guys have any other suggestions. Is Brian Simmons out here anywhere?? I'll bet he can figure it out!!

    Thanks everyone for your replies!
  5. RL1

    RL1 Junior Member
    Messages: 22

    Did you figure it out yet?

    If the solenoid clicks and you can hear the motor getting juice how can the problem be in the harness or from the controller? Only thing I can think of if that is true is it's sending current to multiple solenoids causing it to jam? But I would think you would see some sort of a shudder if that were the case.

    I've been here researching my self because my MM1 SEHP is frozen left and will not lift. Same as you, when it would freeze up I would run it into a snow bank and function would return back to normal. This time it doesnt want to hear it.
  6. dmax 2500hd

    dmax 2500hd Junior Member
    Messages: 18

    Unfortunately, no....very frustrating. Anyone have any ideas here? I don't really know what more to do.
  7. duramaxblade

    duramaxblade Member
    Messages: 71

    This happened to me when I got my last truck. New MM2. Turns out one of the wires in one of the harnesses was cut a little. It was hard to duplicate the problem as well, but they manages to find it. Obviously slamming the truck into the bank helps because you are causing the wires to jostle around and touch again. I want to say it was the main black and red, but I don't remember for sure. The bad connection was actually inside one of the connections where the plow and truck meet. Although they fixed it for free, they said I should always disconnect the plow by grabbing onto the proper spot and not just pulling the wires. Does any of that make sense?
  8. dmax 2500hd

    dmax 2500hd Junior Member
    Messages: 18

    I'll check that out. Thanks for the input.
  9. Brian Simmons

    Brian Simmons PlowSite.com - Sponsor
    Messages: 196

    Well the only way to really diagnose the issue is to test it when it is acting up. From the symptom's given I would think that if you have changed the S-3(required for both raise and angle left) and that did not fix your issue that you have an electrical issue with S-3. A couple of things you can try is first remove the coil cover and verify that both wire clips are tight and well greased. The other is to check the truck side harness (your post claims the plow side was just replaced) to see if there are any breaks in the wire. From time to time we see them break right behind the molded plug. This is usually caused from pulling on the harness instead of the molded plug when it is really cold and they are hard to disconnect. Just an FYI but sometimes metal contamination cannot be found with a magnet if the particles come from the aluminum valve block.

    Last edited: Jan 14, 2009