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Hyd thumb quit working

Frank Posey · 2022-09-14 20:36

2015 JCB JS220 excavator with a Tag Hydraulic thumb. Thumb quit working overnight. Working fine when shut down and at startup the next day it would not retract. Still extends as it should but will not retract. Can activate foot pedal and push thumb into retract position with bucket, but it will not stay retracted and falls back down when bucket is opened. Rebuilt cylinder with all new seals, and no improvement. Checked pressure at thumb and has 3600lbs on the extend side but zero lbs on the retract side. Thumb is activated with a foot pedal using pilot pressure. Checked pilot pressure in both directions and showing 450lbs. Removed spool covers and spool moves in both directions with ease. Spool spring is still in place and tight to spool. No crimps or crushed lines. Any advice is appreciated. Thanks, Frank

Replies8
  1. #1farmerlund2022-09-14 22:44

    Somewhere there is a switch or button the changes it from hammer to thumb. I think you are in hammer mode. One direction oil flow.

  2. #2KSSS2022-09-14 23:59

    Does the thumb actuate with a button or a mechanical foot control? If it is a button on the handle, it would seem that would where I would look next. I had that issue on a CASE CX160. It was a break in the wire on that actuates the hydraulics.

  3. #3uffex2022-09-15 04:04

    Good day Your post may be a simple adjustment as Farmerlund points out one other point be sure the piston in the thumb cylinder has no departed company from the piston rod, normally you can hear a clunking noise as you switch directions. Kind regards Uffex

  4. #4Frank Posey2022-09-15 20:54

    Thanks Farmerlund, I’ll check that first. I hope you are correct, but I’m going to be awfully embarrassed and hate to admit my ignorance if it is that simple. Lol, Mechanic and I have spent several hours checking pressures and head scratching……..

  5. #5Frank Posey2022-09-15 20:55

    Thanks KSSS, it is a foot pedal actuating the pilot valve.

  6. #6Frank Posey2022-09-15 20:57

    We have rebuilt the cylinder (replaced all seals) and verified condition of all internal cylinder parts. Thanks, Frank

  7. #7Frank Posey2022-09-19 21:44

    Farmerlund, you are the Man! There was no physical switch or button pushed, but I went deep into the computer, found the hammer function which was highlighted and unhighlighted it, and the thumb went back to working. I have absolutely no idea how that got activated, but it apparently did. Thank you so much for your insight and assistance!

  8. #8farmerlund2022-09-19 22:20

    Good deal. Glad you got it working. Mine is similar. The flow got changed to 0%. Took awhile to get it figured out. lol