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Blade won't stay up = pressure issue?

Discussion in 'Truck & Equipment Repair' started by TnseVol10, Dec 23, 2008.

  1. TnseVol10

    TnseVol10 Junior Member
    from Maine
    Messages: 2

    Let me ask the obvious question first: do these systems need to be bled like brake lines? That occurred to me after I finished cursing the day I decided to piece this plow together.

    I have an old 7.5' Fisher system with the valve body outside the truck and the pump inside the engine compartment. Went and got the blade after installing the pump, hoses, etc. and if lifted fine (minor engine revving required on my V6) and held for the 30 minute drive home. I nicked one of the hoses while drilling out the holes for the control cables (yes, I know I should have drilled all the holes at once), put on a new hose and now the blade won't go up unless I nearly redline the engine and it doesn't stay once it is up.

    Please tell me I just need to bleed the system.

    If so, to I need to move the valves while bleeding or just have the pump running?

    Oh yeah, I also put a new belt on because the one it called for was really loose. I don't think that is the problem. Truck is a 95 Chevy K-1500.

  2. russ130

    russ130 Senior Member
    Messages: 204

    According to Fisher it can be one of three things, 1- low fluid level, 2- low pump pressure, 3- control handle not actuating valve spool correctly. Perhaps you lost some fluid with the knick and what was in the hose and whatever leaked out while you where changing it. You could also try bleeding it by having someone raise the plow while you loosen the hose at the lift cylinder and then close it once you get no more air.
  3. cbriggs.pm

    cbriggs.pm Junior Member
    Messages: 13

    after i read your headline, i thought o boy, someone i can actually help. then as i read your problem i saw its not a cold weather problem. well im here so my two cents.. iv been having similar problems with my diamond plow, it seems any time below 15 degrees, i have to keep pulling the blade back up as i drive down the road..simple cave man fix for me. put a torch to the box to the box that holds the hydrolic fluid
  4. no lead

    no lead PlowSite.com Addict
    Messages: 1,308

    check all of your power connections. all good? did you fill it with oil? make sure its full. put blade down and fill. angle back and forth first then lift.

    an iso system does not need to be bled. angle first. fill angle fill lift.
  5. daninline

    daninline Senior Member
    Messages: 430

    I had a old Fisher plow tha would go up slow and would creep down when driving and all the valve ajustments were right.
    I ended up changing the valve body it was just worn out. then it was much better.

    I now have a different truck with the same system and I do have a low pressue issue when hot, I have to give it some gas to lift the plow and if I let off the gas when lifting the plow will start to drop.

    Good luck
  6. no lead

    no lead PlowSite.com Addict
    Messages: 1,308

    pretty quiet

    things are quiet tonight guys.
  7. Rob B

    Rob B Junior Member
    Messages: 9

    Having a similar issue, fisher blade goes up fine but drops like 2" and holds...any ideas anyone?
  8. dieselss

    dieselss PlowSite Fanatic
    Messages: 11,392

    air in system, lift ram nut loose?
  9. Rob B

    Rob B Junior Member
    Messages: 9

    It's a new ram, I ll check it tomorrow.
  10. welder1122

    welder1122 Senior Member
    Messages: 115

    its not a mm2 no lead, id go with air in the lines the more u use it and the air shoudl work its way out as long as the resorvor is up stream or u can just bleed it out. crack the line at the lift cylnder and have someone lift the plow and make sure the fluid is full
  11. Rob B

    Rob B Junior Member
    Messages: 9

    Ok, I'm going to bleed it one more time and leave it alone and see what happens.
  12. snowbankr

    snowbankr Member
    Messages: 49

    Those older Fisher Speedcasters are famous for the valve bodies wearing out...metal to metal. No O rings, just a machined hole and machined body. I have had a dozen of these plows and like them better than the elec/hydro units. Positive power, plenty of snot, and a no nonsense "on/off" way of working. I do think the under the hood valve body is better than when it was mounted to the headgear....and when they added power angle...WHOA!! that made plowing so much more easier!! Get a new valve body or make sure the command cable(s) are adjusted in the proper position(s). The raise/lower valve seems to wear out faster than the right/left. Hope this helps.