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Fisher MM2 problems (with video to describe)

Discussion in 'Truck & Equipment Repair' started by plow problems16, Feb 22, 2012.

  1. plow problems16

    plow problems16 Junior Member
    Messages: 10

    Sorry for the long descriptive story here...

    I have a fisher MM2 with an 8 foot HD plow. Problems started after I connected my plow the night before an approaching storm. Everything worked fine that night and the next morning when I went to work. The "approaching" storm turned out to be a big nothing. No accumulation. I work 24 hour shifts so the plow stayed on my truck while I stayed at work. After a very cold night I got off work at 7am and went to leave and the plow wouldn't move at all. The motor was running just not enabling the plow to angle or raise. Opened the reservoir and saw it was a bit low so I added fluid which got it to work again. So I decided to do some maintenance and replaced the gland nut on the up/down cylinder and also changed the fluid. I used all correct fluids and parts. Since doing that Im having all sorts of problems. To me it seems like it has air in the system but I can't, for whatever reason, get all the air out. With the right amount of fluid I can angle the plow left and right fine. I can't however raise the plow consistently. If I angle it back and forth 10 or so times, I am able to make it raise 75% of the full extension of the piston and that cylinder holds the weight of the plow up without any leaks or anything. However when it is raised I cannot angle the plow by using the stick. I can move the plow left and right freely with one hand when it is in the raised position. While the plow was in the up position I would crack the fitting at the base of the cylinder and every time air filled hydraulic fluid would come out as the piston would slowly lower. And when the piston would finally lower all the way it would let out one last burst of air. I would then tighten that fitting, add more fluid and repeat the process with no success.

    I also changed the air bleeder which didn't change anything. I recorded a video for you to watch which shows how I can angle it but not raise it.

    Any ideas? Thanks in advance.

  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    All the classic signs of a common issue. Good chance the pickup tube is off the pump and lying in the bottom of the reservoir.
  3. plow problems16

    plow problems16 Junior Member
    Messages: 10

    Pickup tube as in the part that sucks up fluid into the manifold from the reservoir? Is there an easy way to check this instead of pulling the whole unit?
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Correct, that's the tube I was referring to. And to access it you need to drop the reservoir, which is probably long overdue anyway to clean all the sludge out of the bottom.

    If it's been a long time since it was last removed it's best to pull the unit off and work on the reservoir an it's attaching screws on the bench as they have a nasty habit of corroding in and to the manifold, making removal a daunting task most times.

    Anti-seize is your friend during re-assembly. :salute:
  5. plow problems16

    plow problems16 Junior Member
    Messages: 10

    B & B you are a life saver bro...lol.

    Im adding some video for others that might run into this problem.

    Pulled the reservoir today (luckily the screws were easy to remove) to find the pickup tube floating in the hydraulic fluid


    Drained fluid from reservoir where you can clearly see the pickup tube at the bottom.


    Put it back in place


    Refilled fluid and worked the air out of system and added more fluid and got it back to proper working order


    My only other questions.... when I release the plow from a raised position and allow gravity to do its thing, you see the piston go back down ( in the last video). Once the weight of the plow is on the ground the piston does not have a smooth return back to its lowest position. It drops a few inches then stops, then drops a few more inches then stops, etc. Could this be due to gland nut being too tight? I could also just re adjust the tension spring which helps pull the piston back down. And also, does the pump motor sound odd at all to you? To me it sounds like it has more vibration in it when running. This summer ill pull the whole thing and clean it all out and tighten all bolts and fittings to spec.

    Anyways, thanks again. Saved me a lot of frustration. Now hopefully we get some snow around here.
  6. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Up and running again, good job. Although you weren't aware of it now and this would've been a good opportunity to add it there is an updated pickup kit with a retainer to keep this from happening again. I don't always use the "kits", rather just make my own retainer bracket real quick but you can pick one up from the dealer and add it later if it falls off again, or while servicing the unit before next season to prevent the issue permanently.

    The chattering ram is simply because you replaced the nut. May just be just a little too snug but they'll normally wear in during use too as long as it isn't too too tight. But if it doesn't smooth out after some use just back the nut off slightly and it should settle down.