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Older Fisher Model Plow Question

Discussion in 'Commercial Snow Removal' started by ksland, Nov 30, 2003.

  1. ksland

    ksland Senior Member
    from ma
    Messages: 419

    I have an older full hydraulic fisher 8' plow. The problem is this, once the truck gets warm from driving a while, when I push up on the joystick to raise the plow it actually goes down slowly at low rpm. It will raise with the rpms of the truck up higher than say 2000. It angles fine and works fine cold although it seems as if it should raise quicker. Basically when warm the plow raises slower and not at all even drops at low rpms. The plow belt and pulleys are new and tight. Weak pump maybe? An adjustment?
  2. ksland

    ksland Senior Member
    from ma
    Messages: 419

    The fluid is all fresh and full also.
  3. mowahman

    mowahman Junior Member
    Messages: 28

    Is your valve body mounted under the hood, on the inner fender? I have 4 of these set ups and have had to replace the valve bodies. The lift and angle cylinders in the valve itself are a metal to metal fit. There are no O rings or any other "replaceable" parts in the valve itself. As for the plow lifting OK when first starting out, the fluid is thicker when cold so it takes up some of the "slack" around the cylinders in the valve.

    When I replaced mine, I used Fisher parts. I am sure that someone makes their valves for them, or are a mass produced valve that Fisher uses. They are rather pricey at the dealer, but, then again, what isn't?? It is still cheaper than pullin' your hair out and lifting the plow every 15 seconds when out plowing for 15 hours. Trust me on that one.

    Hope this helps... and remember..keep your plow on the ground!!
  4. ksland

    ksland Senior Member
    from ma
    Messages: 419

    My plow doesn't drop when the joystick is in the middle. I have had plows that would droop slowly when sitting, this stays at the same height. Once hot or warm at low idle pushing up on the joystick the plow will slowly drop. If I give it a little gas it goes right up. Not saying that the problem isn't as you said, just figured I would correct you on that. You think it would still be that, ANYONE else?
  5. smwmarc

    smwmarc Junior Member
    from Maine
    Messages: 14

    I have a similar problem with my Diamond and I was talking with my mechanic about it yesterday. He suggested that maybe it was the pump not giving enough pressure. Something like the tolerance in the pump is too great to keep up pressure at idle speed, but when engine is reved it will work. And since the tolerance is too great when the oil is warm it is more fluid and slips by the pump action easier. I suggested that if it was a pump problem then I would think that the angling cylinders would be slow as well, but since they do not seem to be as slow I thought maybe it was a valve problem. I am going to have him working on it this week so we will hopefully find out. The only other things to rule out would be some sort of leak in that line or some obstruction not excepting a damaged cylinder.
  6. snowplowman

    snowplowman Junior Member
    from NH
    Messages: 12


    Most of the time in this case the valve body is going bad as the pump doesn't hold pressure in the piston , the valve body does, but if it is slow in raising then it could be the pump. A dealer could probably tell you which one. The pump is 258 and the valve iis 352. either way they are pricey, but will save you lots later.
  7. sped65

    sped65 Junior Member
    from CT
    Messages: 1

    Plow Pump Problem

    I had the same problem you described with my plow pump. I figured I had nothing to lose since it would hardly lift the plow any longer when the fluid was hot. I was constantly revving the engine to get the plow to move. Anyway the only way to take it apart was to cut it open. You will see the back of the tank is welded. I cut all the way around with a band saw and then unscrewed the back form the pump. Then you can get at the pump body which has a 90 on the back with a screen on it. I cleaned the screen, which was clogged pretty good put it back together and welded the tank back together. Has worked great ever since! A new one at the time would have been $125 so it wasn't that big a deal but earned me bragging rights with the guys in the shop.

    What you describe is exactly what happened to me, still using the same valve.