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Fisher MM2 won't go up = Bad motor

Discussion in 'Truck & Equipment Repair' started by peterzereski, Dec 27, 2010.

  1. peterzereski

    peterzereski Junior Member
    from RI
    Messages: 12

    So I am new to the site but not new to plowing or internet forums. This site is great as it offers lots of great info. One thing that I noticed while sorting out my problem is that many people don't conclude there posts with a resolution to the problem.

    So here's my story.

    MM2 Manufactured in 2005 with minimal maintanace used pretty hard.

    Put her away last spring working fine/normal, put it on for this most recent storm and I got no movement in any direction from the plow.

    When I tried to raise, lower or angle the blade I could hear the relay under the hood clicking, but no movment.

    I cleaned and electro greased all truck to plow fittings....still nothing, but I could feel the wires connecting the truck to the plow motor heating up.

    I broke out my multi meter (you could also use a 12V test light) and determined that the relay was sending power to the truck grill connector coupler, when I tried to move the plow in any direction, 14.5 volts to be exact which is fine. There was a little less right at the plow motor (about 11 volts), but I guess this is normal.

    So step one is to check the truck side electrical system, start with fuses, then check the relay, which should engage when you try to raise,lower or angle the plow. You should here a snap/click sound at the relay and see about 12 volts on your meter measured at the relay. If you don't hear the relay or get 12 volts during plow operation than you likley have a bad relay. It could also be a blown fuse or bad ground, so check all the above.

    In my case I was sure the relay was fine and that the plow was getting power. Then just to make sure I connected 12 volts directly to the plow motor using a set of jumper cables. Attach the positive end of the jumper to the positive terminal on the plow motor (it usualy has a + on it somewhere) and the attach the negative end of the jumper cable to the negative terminal on the plow motor. Then just connect the negative end of the jumper cable to your truck battery and touch the positive side of the jumpers to the positive side of the battery and see if the plow motor comes on.

    After trying this direct 12 volt test with jumper cables I got nothing, but lots of sparks. The motor didn't come on, but I could feel this clicking which I am still not sure if that feeling was just coming from the relay inside the truck or if it was the motor trying to turn.

    So at this point I was confident that the problem was on the plow side of the electrical system, so I resigned myself to tareing down the motor and hydro system on the plow.

    Its really not that hard if you are mildly mechanicly inclided and have a decent socket set, allan wrench set, small and large cressent wrench's, rags clean heated work space, break free spray and some common sense you will do fine.

    Although its not neccasary to remove the entire power head unit to remove the motor I had never worked on a plow and having all the hoses and the plow frame in the way just seemed annoying. So I un hooked the truck, closed the garage door and turned on the diesel heater and drained all the hydro fluid out, which looked like it had a little water and sludge in it, but wasn't as bad as I thought it might be.

    So with fluid drained I used to wrenches to remove the hydrolic hoses from the hydro pump on the plow. Use one wrench to turn the fitting and the other to apply stationary suppoting force to the hose end. The idea is to remove the fitting without spinning and damaging the hydro hose.

    Then I sprayed a little break free around the bottom of the motor where it meets the hydro block. Next I removed the two bolts and nuts that hold th entire power unit to the plow frame and carefully removed the entire power head from the plow.

    I placed it on the graound near the heater and let it warm up for a while. Then I removed the fluid resivor pan by removing the 4 screws onthe underside. It was a little tough to remove, but the heat certainly made it easier than it would have been otherwise. There is a O ring that seals the resivor pan to the bottom of the hydro unit, if removed carefully the O ring may be re-used if it looks ok, but if you can replace it with a new one.

    So with the resivor pan removed I cleaned all the sludge from the bottom and cleaned the magnet, which I checked for metal fillings. The magnet is there to attract metal pieces that shear and wear from differant parts of the power unit. Mine just had some grey residue and a few very small specks of metal.

    Next, I removed the 5 bolts that attach the hydro pump to the hydro block. I carefully set it aside making sure not to loose any of the O rings or other parts.

    With the hydro pump removed you can look inside the pump shaft hole and see the drive notch of the electric motor. Its just a slot, so I carfully inserted a good flat head screwdriver into the slot of the motor to see if I could manuly turn it.

    I could not turn it with hand force so not wanting to damage anything insiad the hydro pump shaft I decided to remove the electrit motor from the hydro block. I removed the two full length bolts on the top of the motor and right away it didn't look good. The bolts were wrapped in paper to keep them insulated from the eletricity in the motor, but the paper looked all burnt and wet with green residue on them.

    The break free spray did its job and with a few light taps froma hammer I was able to remove the motor. If your real careful here you might be able to get one more storm out of a siezed motor by just cleaning the aramature and brushes. In my case however the armeture was siezed right to the hydro block so when I tried toremove the motor just the motor housing came off. It was chock full of green corrosion and smelled burnt.

    With the motor housing off I used my hand to wiggle and gently twist the motor ameture until it broke free. I then attempted to clean the inside of the motor housing using a properly sized wire wheel, which worked great. But when I tried to remove the top of the motor housing I broke one of the parts the holds the motor brushes in place, renduring the motor....junk. If I had been more carful in removing the motor and housing I probably could have got it to work for the time being, but it was getting late and I was getting tired.

    So the next morning I went to the plow shop and bought a new electric motor, some new hydro fluid and filters. I gently removed all scale and build up from all parts of the power head, especialy the area whene the hydro fluid resivor meets teh hydro block, greased up the large O ring and put everything back together in less than an hour.

    She now works like new, and I will be sure to doa better job covering the plow power head in the off season from now on, as the fisher design of motor to hydro block is NOT water tight, so water gets in there, where it sits in the hydro block shaft and starts to rust leading to a siezed motor.
  2. peterzereski

    peterzereski Junior Member
    from RI
    Messages: 12

    Couple of key points...

    Plow worked fine last season.

    Plow would not move up or down left or right.

    Headlights and everything else seemed to operate normally.

    When I tried to move the plow with the control stick the lights in the truck would dim, more so than usual.

    After a few tries and during testing with a multi meter I could feel the power wires coming from the plow were getting very warm to the touch.

    My plow electric motor also looked crappy,lots of rust and not too much paint.

    Stored outside, uncovered....(not anymore!)
    Last edited: Dec 27, 2010
  3. joehawth

    joehawth Junior Member
    Messages: 1

    looks like i have the same problem with relay clicking and nothing happening
    measured ~12v at the motor terminals when control activated

    to replace the motor do you have to drain the hydro fluid or will the electric motor pull right out of the pump assembly leaving the pump assebly sealed?
    thanks joe
  4. peterzereski

    peterzereski Junior Member
    from RI
    Messages: 12

    Sorry for the delay in resonse, but the site wouldn't let me log on though I did try.

    Anyways....no you don't have to drain the fluid, but if its seized bad enough you will have a tough time getting the armeture of the motor to seporate from the hydro pump.

    Best tip....hit the area where the motor connects to the hydro block with a little "break free" and let sit for a while before you try to remove the motor.