6 hours ago
Picture this: a robust John Deere 690B is cruising forward and backward just fine—but when you attempt to pivot, nothing happens. It’s like turning the steering wheel—and getting nowhere. This problem can be frustrating, but understanding the root causes transforms confusion into opportunity.
Understanding the Pilot System & Steering Dynamics
A veteran operator once faced a stubborn 690B that refused to turn at a job site’s narrow entrance. After hours of futile attempts, he discovered that his machine was stuck in rabbit mode—steering flow was pinched. Switching into turtle mode restored full turning power. A quick run of pilot and main system checks later, he found a worn solenoid coil that got replaced—and driving woes vanished.
Understanding these hydraulics and valve dynamics means no more stuck straight—just smooth, confident pivots from here on.
Understanding the Pilot System & Steering Dynamics
- The 690B uses a pilot hydraulic system—a low-pressure circuit that activates main, high-pressure control valves.
- If pilot pressure falters—say, dipping below ~500 psi—the main steering valve may not fully open, blocking track control and preventing turns. An actual customer once measured a control valve pressure of around 1800 psi, but suspected the pilot system was weak, preventing full functionality.
- Later checks revealed electrical gremlins: two magnetic solenoids near the cab control the shift between high and low speed ranges. In low speed (“turtle”), both sides receive full flow—making turns stronger. In high speed (“rabbit”), flow diverts to only one section of each track motor, reducing turning power.
- Forward and reverse movements remain unaffected.
- Attempts to stop one track do not induce a pivot.
- Steering improves notably in low-speed rather than high-speed mode.
- Control pressure registers, but turning still fails.
- Pilot pressure deficiency—often due to worn seals, leaks, or faulty pilot control components.
- Solenoid malfunction or misalignment—especially in the dual-speed flow valve near the operator station.
- Insufficient main pressure, meaning the main valve never opens wide—despite visible pressure on test ports.
- Measure boom cylinder pressure: tapping into the boom raise circuit with a 3000 psi gauge helps benchmark your relief valve setting.
- Inspect solenoids and wiring: ensure both turtle/rabbit mode valves operate correctly. Replace any faulty magnetic coils or check their electrical feed.
- Test the pilot circuit directly: check pilot pressure under load; confirm it meets the minimum threshold (usually ~500 psi).
- Check test port data: pressing directly on control valve ports while operating may reveal pressure drops or blockages.
- Evaluate shifting between high and low ranges: note whether steering ability drops noticeably in high-speed mode—this often indicates flow diversion rather than pilot failure.
- Regular pressure audits: periodically capture pilot and main pressure readings to detect deterioration early.
- Keep shift control electrics clean and moisture-free, especially around the cab—electrical issues here are often overlooked.
- Operator technique matters: when tight turns are needed, shift into low-speed first and lower the bucket to unweight the drive system.
- Use replacement seals wisely: for aging machines, replacing worn pilot seals can restore functionality without costly overhauls.
- Pilot Hydraulic System: a low-pressure circuit that actuates the main valve control—critical for steering response.
- Solenoid Valve: an electrically activated valve controlling flow paths for high/low speed and track motor supply.
- Turtle/Rabbit Mode: a speed range selector—“turtle” = low speed/high torque; “rabbit” = high speed/lower torque.
- Control Valve: directs hydraulic flow to track motors for propulsion and turning.
- Test Port (JIC cap): access point to measure hydraulic pressure with a gauge.
- Issue: Machine can drive but cannot steer or turn as expected.
- Likely Culprits:
- Bad pilot pressure (below ~500 psi).
- Faulty solenoid shift control between speed ranges.
- Main valve not opening completely due to pressure or pilot failure.
- Bad pilot pressure (below ~500 psi).
- Steps to Diagnose:
- Measure test port/boom cylinder pressures.
- Examine solenoid wiring and function.
- Test in both speed modes (“turtle” vs “rabbit”).
- Measure test port/boom cylinder pressures.
- Fixes:
- Replace worn pilot seals or solenoids.
- Repair or clean pilot circuit leaks.
- Train operator to shift wisely and use weight transfer tricks.
- Replace worn pilot seals or solenoids.
A veteran operator once faced a stubborn 690B that refused to turn at a job site’s narrow entrance. After hours of futile attempts, he discovered that his machine was stuck in rabbit mode—steering flow was pinched. Switching into turtle mode restored full turning power. A quick run of pilot and main system checks later, he found a worn solenoid coil that got replaced—and driving woes vanished.
Understanding these hydraulics and valve dynamics means no more stuck straight—just smooth, confident pivots from here on.
