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JD 35G excavator thump only works in one direction

M

MOOSEHEAD101

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Joined
May 16, 2026
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5
Location
OHIO
I just picked up a 36 g mini ex, i switched the hoses around at cylinder and it worked the other direction,
When i first start up the thumb moves to full close automatically ........ any help would be appreciated
 
M

MOOSEHEAD101

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Joined
May 16, 2026
Messages
5
Location
OHIO
screenshot-2025-08-13-at-5-38-25%E2%80%AFam-png.346201
 
Allan M

Allan M

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Oct 20, 2020
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165
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95037
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Semi-retired: Strategic planner/author
Hey Moosehead 101:

I did a quick AI search on this machine for you. The sources were: Green Tractor Talk, Contractor Talk, Boom & Bucket and unknown generic sources on the web. The troubleshooting described here may help your discovery process. It appears to be a common issue and thus a lot of data available on the topic. Personally, given the issues I've had with mice, I'm always suspicious of a chewed through wire somewhere in the system. Good luck. A

When a JD 35G excavator thumb stops working in both directions, the most common culprits are an inactive auxiliary hydraulic circuit, a loose or damaged electrical connection at the joystick or solenoid, or a stuck valve spool in the auxiliary block. [1, 2]
Troubleshoot the issue using these specific steps:

1. Check the Auxiliary Mode / Switch
  • Selector Valve: Ensure the manual selector valve on the hydraulic block (located on the arm/dipperstick) is turned entirely to two-way flow (often labeled as "Thumb" mode) rather than one-way hammer mode.
  • Auxiliary Activation Switch: Many JD models require you to flip a physical auxiliary activation switch or rocker on the right-hand console (near the monitor or beneath the safety lever) to send power to the thumb circuit. Verify that this switch is turned on and the circuit is active.

2. Inspect Electrical Connections
  • Joysticks: The rocker switch on your right joystick relies on small gauge wires (often around 22ga) that flex whenever you move the stick. Inspect the base of the joystick for broken, pinched, or loose wires.
  • Solenoids: Check the wiring harness leading to the auxiliary hydraulic solenoid valves behind the operator's seat or under the cab floor. Trace the wires to ensure none have been chewed by rodents. Test for \(24V\) power at the solenoid with the ignition on and the rocker switch engaged.

3. Check for Stuck Valve Spools
  • If the electrical signal is reaching the solenoids but the thumb still won't move, the hydraulic spool may be mechanically stuck. Locate the auxiliary spool valve (often under the side floor panel or compartment under the seat). Check if the spool is free and manually exercise it to dislodge any debris or hydraulic lock.
 
M

MOOSEHEAD101

Member
Joined
May 16, 2026
Messages
5
Location
OHIO
Check for Stuck Valve Spools
  • If the electrical signal is reaching the solenoids but the thumb still won't move, the hydraulic spool may be mechanically stuck. Locate the auxiliary spool valve (often under the side floor panel or compartment under the seat). Check if the spool is free and manually exercise it to dislodge any debris or hydraulic lock.

  • sounds like my issue . any steps i can flow would be helpful.
 
Allan M

Allan M

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Oct 20, 2020
Messages
165
Location
95037
Occupation
Semi-retired: Strategic planner/author
Moosehead101: This is the diagnostic procedure that came up from Green Tractor Talk for your model excavator. I have no idea if this is exactly correct. If you don't have one it might be worth purchasing a JD service manual for this machine before getting deeper into the issue. There are also usually Ytube videos that show various procedures. Given this machine has been around a bit I don't doubt someone else has encountered this issue and made a video of it. Also, I'm sure there are JD owners on this site and maybe a few can add their thoughts. I had a similar issue on my Kubota U55-4 but my machine has a operator control screen where you can adjust and set hydraulic flows for implements. When I bought the machine I suspect they were using a hammer and had the thumb icon set to one-way flow (the manual valve on the hydraulic control block was set to two-way). I corrected that and life was good. Hope this helps. Note: I believe your machine uses all manual control settings.

To unstick the auxiliary spool valve on a John Deere 35G excavator, safely release all residual hydraulic pressure, then access the main control valve under the cab floor. Remove the auxiliary solenoids or end caps, manually push and cycle the exposed spool using a punch, and clean away any debris.

Step-by-Step Instructions

1. Relieve System Pressure
Excavator hydraulic lines retain pressure even with the engine off.
  • Turn the ignition key to the ON position (do not start the engine).
  • Lower the safety lever/lockout bar.
  • Cycle the joysticks and the auxiliary foot pedal/switch back and forth several times to dump trapped pressure into the return line.
  • Turn off the machine completely.

2. Access the Spool Valve
  • Remove the floor panels inside the operator's cab to expose the main hydraulic control valve block.
  • Locate the auxiliary spool valve section. It is typically the section with pilot lines or an electrically actuated solenoid on top.

3. Inspect and Manually Unstick the Spool
  • If your auxiliary is controlled by an electric solenoid (like a thumb), carefully remove the solenoid coils from the valve stem.
  • With the spool ends exposed, use a brass punch or a suitable blunt tool to gently push the spool in and out.
  • If it is binding, apply a quality penetrating oil (like PB Blaster or WD-40) around the edges of the spool to help break up varnish or minor corrosion.
  • Gently tap the spool back and forth until the spring returns it naturally and it slides smoothly by hand.

4. Check for Debris or Damage
  • If the spool remains tight, the valve block may contain debris or a mechanical burr.
  • Clean the valve chamber thoroughly and inspect the O-rings for cuts or pinching.

5. Reassemble and Test
  • Reinstall the solenoid or end caps and torque them to the manufacturer's specification.
  • Start the machine at a low idle, activate the auxiliary circuit, and slowly cycle it back and forth to purge any air from the lines.
 
L

laidback01

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Nov 5, 2013
Messages
245
Location
West Glacier, MT
the simpler thing might be the accessory valve? I have no idea what it's really called, or if you even have it. On my 50 ZTS, I have a valve I turn with a 15/16 wrench CW or CCW. One direction the foot pedal will open/close the thumb. the other direction on that valve, the foot pedal lets a LOT more fluid flow, but only one direction - for a plate compactor or hammer. But besides that, if you are dealing with stuff moving without your input... well, something else is screwy.
 
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