10-22-2025, 12:01 AM
A Case 688 excavator showing sluggish hydraulic response and delayed directional changes may suffer from low system pressure or misadjusted load-sensing valves. Even with sufficient lifting power, slow operation can stem from overlooked control settings or fluid compatibility issues.
Case 688 Excavator Overview
The Case 688 was introduced in the late 1980s by Case Construction Equipment, a division of CNH Industrial. Designed as a mid-size wheeled excavator, the 688 featured a Cummins diesel engine, closed-center hydraulic system, and load-sensing control valves. It was widely used in municipal and utility work, especially in Europe and North America, where its mobility and reach made it ideal for roadside excavation and trenching.
Case sold thousands of 688 units globally, and many remain in service due to their mechanical simplicity and rebuildable components. The hydraulic system was designed to balance power and efficiency, using pressure-compensated valves to adjust flow based on demand.
Terminology Note
After rebuilding the engine and inspecting the hydraulic pump, a newly acquired Case 688 exhibited slow operation across all functions. The machine could lift itself and dig with adequate force, but movement was sluggish and directional changes had a noticeable two-second delay. The hydraulic oil used was Travelers Premium, which claims compatibility with Case MS-1230, but performance remained subpar.
The previous owner had noted slow operation, but the new operator found it significantly worse than expected. This discrepancy suggested either a progressive decline in system responsiveness or a misadjusted control setting.
Key Diagnostic Insights
In Mississippi, a technician working on a Case 888—similar in design to the 688—found that adjusting LS1 and LS2 restored full hydraulic speed after months of sluggish operation. The valves had been backed off too far during a previous repair, reducing system pressure below optimal levels.
Another operator in New York noted that switching to a higher-grade hydraulic oil improved responsiveness slightly, but full performance was only restored after fine-tuning the LS valves.
Conclusion
Hydraulic slowness in the Case 688 excavator often stems from misadjusted load-sensing valves rather than pump failure or fluid incompatibility. With careful tuning of LS1 and LS2, operators can restore full responsiveness and eliminate directional delays. The machine’s design allows for field adjustments, making it a durable and serviceable choice for long-term use. Understanding the sensitivity of these valves is key to unlocking the full potential of the 688’s hydraulic system.
Case 688 Excavator Overview
The Case 688 was introduced in the late 1980s by Case Construction Equipment, a division of CNH Industrial. Designed as a mid-size wheeled excavator, the 688 featured a Cummins diesel engine, closed-center hydraulic system, and load-sensing control valves. It was widely used in municipal and utility work, especially in Europe and North America, where its mobility and reach made it ideal for roadside excavation and trenching.
Case sold thousands of 688 units globally, and many remain in service due to their mechanical simplicity and rebuildable components. The hydraulic system was designed to balance power and efficiency, using pressure-compensated valves to adjust flow based on demand.
Terminology Note
- Load-Sensing Valve (LS Valve): A hydraulic control valve that adjusts pump output based on system demand, improving efficiency.
- Closed-Center System: A hydraulic configuration where flow is blocked until a function is activated, reducing heat and wear.
- Directional Delay: A lag in response when switching between forward and reverse travel or swing directions.
- Travelers Premium Hydraulic Oil: A multi-purpose fluid marketed for compatibility with Case MS-1230 specifications.
- LS1 and LS2 Adjusters: Manual screws on the valve block used to fine-tune pressure settings for different hydraulic circuits.
After rebuilding the engine and inspecting the hydraulic pump, a newly acquired Case 688 exhibited slow operation across all functions. The machine could lift itself and dig with adequate force, but movement was sluggish and directional changes had a noticeable two-second delay. The hydraulic oil used was Travelers Premium, which claims compatibility with Case MS-1230, but performance remained subpar.
The previous owner had noted slow operation, but the new operator found it significantly worse than expected. This discrepancy suggested either a progressive decline in system responsiveness or a misadjusted control setting.
Key Diagnostic Insights
- Pump condition was verified during rebuild, showing no internal damage or wear.
- Hydraulic pressure appeared sufficient, as the machine could perform heavy lifts.
- System-wide slowness pointed to a control issue rather than a mechanical fault.
- LS1 and LS2 valves were identified as potential adjustment points. These valves regulate pressure thresholds for different hydraulic circuits and are highly sensitive—adjustments should be made in ¼-turn increments.
- Locate LS1 and LS2 adjusters on the valve block. Turn inward (clockwise) to increase pressure, outward to decrease.
- Make small adjustments—no more than ¼ turn at a time—and test machine response after each change.
- Monitor system pressure with a gauge during operation to confirm changes.
- Ensure hydraulic fluid meets Case MS-1230 standards and is free of contamination.
- Check for air in the system, especially after pump or hose replacement. Bleed lines if necessary.
- Replace hydraulic filters every 500 hours or annually.
- Use only approved fluids with correct viscosity and additive packages.
- Inspect valve bodies for corrosion or wear that may affect adjustment accuracy.
- Keep a log of pressure settings and performance changes to track system behavior.
- Train operators to recognize early signs of hydraulic lag, such as delayed swing or travel hesitation.
In Mississippi, a technician working on a Case 888—similar in design to the 688—found that adjusting LS1 and LS2 restored full hydraulic speed after months of sluggish operation. The valves had been backed off too far during a previous repair, reducing system pressure below optimal levels.
Another operator in New York noted that switching to a higher-grade hydraulic oil improved responsiveness slightly, but full performance was only restored after fine-tuning the LS valves.
Conclusion
Hydraulic slowness in the Case 688 excavator often stems from misadjusted load-sensing valves rather than pump failure or fluid incompatibility. With careful tuning of LS1 and LS2, operators can restore full responsiveness and eliminate directional delays. The machine’s design allows for field adjustments, making it a durable and serviceable choice for long-term use. Understanding the sensitivity of these valves is key to unlocking the full potential of the 688’s hydraulic system.
