Mini Excavator hydro thumb install question

Discussion in 'Heavy Equipment & Pavement' started by swanny, Jun 17, 2011.

  1. swanny

    swanny LawnSite Senior Member
    Messages: 660

    Machine is a Komatsu PC27-8...3 ton approx., early 2000 year. Plumbed from factory for auxiliary attachments. Ram on thumb is double acting. When I plumb it one way it functions in both directions, but has very little downwards pressure. Swap lines to the cylinder ports and it has great downwards pressure but doesn't open.

    I'm guessing my auxiliary is only a loop with pressure in one direction (as I can only see one line jump when I work the valve)?

    I'm thinking I need a single acting cylinder that I only plumb with the pressure side as the internal spring will open it back up when I let off with the pressure?

    Any one have any ideas? Thanks much!
  2. 74inchShovel

    74inchShovel LawnSite Member
    Messages: 108

    On my TB135 there is a lever that makes auxiliary flow one direction only, it is engaged when putting on a hammer. If I take my hammer off, but dont switch the lever back my thumb will act just like what you are saying. I wonder if your machine has a lever like this? I think its purpose is to reduce hydraulic pressure spikes from the hammer.
  3. SiteSolutions

    SiteSolutions LawnSite Bronze Member
    Messages: 1,114

    Maybe you've got a flow restriction on the line that is giving the poor results? Probably start by asking the folks you got the thumb from.
  4. swanny

    swanny LawnSite Senior Member
    Messages: 660

    I knew it was something simple I was possibly overlooking. Forgot all about that lever as it's tucked up underneath the body. THANKS!!!!!! Works great.

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