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Why Add Auxiliary Hydraulics?
Adding a hydraulic thumb to the John Deere 690B greatly enhances its ability to grasp, sort, and hold materials—making it more efficient for demolition, landscaping, and debris handling. However, the 690B originally comes with an open‑center hydraulic system, which complicates the process of adding auxiliary hydraulics without disrupting existing functions.
Common Strategies Explored
Operators and technicians typically consider several retrofit approaches:
Here’s how one operator ultimately equipped his machine:
Real‑World Anecdotes and Insights
A seasoned mechanic recalled a similar project from decades ago—he emphasized the importance of including a crossover or circuit relief to prevent damage when the thumb encounters resistance during retraction. Without it, structural damage can occur under load.
Other retrofit enthusiasts often flagged two key concerns:
Retrofitting auxiliary hydraulics the right way preserves existing controls, adds functional versatility, and avoids the pitfalls of bypassing or overloading the hydraulic system. With careful planning and key safety components—like relief valves—operators transform aging trackhoes into wildly productive tools without breaking the bank.
Adding a hydraulic thumb to the John Deere 690B greatly enhances its ability to grasp, sort, and hold materials—making it more efficient for demolition, landscaping, and debris handling. However, the 690B originally comes with an open‑center hydraulic system, which complicates the process of adding auxiliary hydraulics without disrupting existing functions.
Common Strategies Explored
Operators and technicians typically consider several retrofit approaches:
- T‑in with a Selector Valve
Diverting flow from existing hydraulic lines using a selector (diverter) valve to power the thumb selectively.
- Installing a Dedicated Subplate and Directional Control Valve
Tap into the main supply and return, then mount a subplate with an additional directional‑control valve specifically for the thumb function.
- Adding an Independent Hydraulic Pump
Drive a separate pump via the fan belt to power the thumb without interfering with the open‑center system.
Here’s how one operator ultimately equipped his machine:
- Confirmed the trackhoe uses an open-center system rated around 2,500 psi and 18 GPM.
- Tapped into the main supply and return lines.
- Mounted a DO5 subplate with a tandem-center directional-control valve.
- Installed a double relief valve (cushion valve) in the circuit to protect against overpressure when reversing cylinder motion.
- Controlled the thumb using a momentary on/off/on rocker switch mounted on the stick lever.
- Totaled approximately $285 for valves, $400 for hoses and fittings, and around $900 for the hydraulic thumb, instead of paying several thousand for a pre‑built kit.
Real‑World Anecdotes and Insights
A seasoned mechanic recalled a similar project from decades ago—he emphasized the importance of including a crossover or circuit relief to prevent damage when the thumb encounters resistance during retraction. Without it, structural damage can occur under load.
Other retrofit enthusiasts often flagged two key concerns:
- In open‑center systems, simply T‑ing into a line often results in oil bypassing the attachment, flowing straight to tank. Effective auxiliary circuits require placing the control valve inline, capable of managing full flow even when idle—but such valves are typically large and expensive.
- Electric diverter valves placed in another circuit (e.g., bucket tilt) can substitute, but they shift functionality rather than add it—leaving operators one function short unless another dedicated circuit is installed.
- Open‑Center Hydraulic System: A hydraulic setup where oil flows through the control valve back to tank when no command is given.
- Directional‑Control Valve (DO5 Tandem-Center): A spool valve that can direct flow independently to extend or retract a cylinder, with a neutral center that allows flow back to tank.
- Subplate: A mounting base for adding extra valves onto the main valve stack.
- Relief / Cushion Valve: A safety valve that bypasses excess pressure or cushions movement to prevent damage or shock in the system.
- Selector / Diverter Valve: A valve that reroutes flow from one function (e.g., bucket tilt) to another (e.g., thumb) when activated.
- Momentary Rocker Switch: An electrical control that toggles between functions only as long as it’s held in position.
- Identify and confirm system type and capacity (open‑center, 2,500 psi, 18 GPM).
- Tap into both main hydraulic supply and return lines.
- Install a subplate to mount a dedicated tandem-centre directional valve.
- Add a double relief valve to protect against pressure spikes during thumb retraction.
- Mount a momentary rocker switch on the control lever for intuitive thumb control.
- Route hoses and fittings professionally—preferably using a hydraulic supply technician to ensure safe and tidy plumbing.
- Budget the components wisely: valves ($285), hoses/fittings ($400), thumb attachment (~$900).
Retrofitting auxiliary hydraulics the right way preserves existing controls, adds functional versatility, and avoids the pitfalls of bypassing or overloading the hydraulic system. With careful planning and key safety components—like relief valves—operators transform aging trackhoes into wildly productive tools without breaking the bank.
