Rebuilding the Hydraulic Control Valve on a Bobcat 743 Skid Steer

[MikePhua]

The Bobcat 743 and Its Hydraulic Architecture
The Bobcat 743 was part of the brand’s early generation of skid steer loaders, introduced in the 1980s by Melroe Manufacturing Company, which later became Bobcat Company under Ingersoll Rand and eventually Doosan. With a rated operating capacity of 1,300 lbs and a robust mechanical layout, the 743 earned a reputation for reliability and ease of service. Its hydraulic system is central to its performance, powering lift arms, tilt functions, and auxiliary attachments through a manually actuated control valve.
Over time, wear in the hydraulic control valve can lead to internal leakage, sluggish response, and unpredictable behavior. Rebuilding this valve is a critical maintenance task that restores precision and prevents further damage to the pump and cylinders.
Symptoms of Valve Wear and Internal Bypass
Operators often notice several key symptoms when the control valve begins to fail:

• Fluid squirts from the spool area when the auxiliary lever is moved
  
• Lift arms slowly drop over time even when not in use
  
• Tilt pedal behavior becomes erratic—pressing forward lowers the bucket, but pressing backward causes a momentary drop before lifting
  
• Overall hydraulic response feels delayed or inconsistent
  

These issues typically stem from worn O-rings, degraded seals, or scoring on the spool lands and valve bores. Internal bypass allows pressurized fluid to leak past the spool, reducing effective pressure at the actuators.
Disassembly and Valve Identification Challenges
Removing the valve from the loader is a labor-intensive process, often requiring partial cab disassembly and careful labeling of hydraulic lines. Once removed, identifying the valve type is essential. While many manuals reference Gresen valves, the Bobcat 743 may be equipped with a Melroe-branded valve, which differs in internal layout and seal dimensions.
Operators should:

• Compare the valve body casting numbers with service documentation
  
• Photograph each spool and spring assembly before disassembly
  
• Use a clean work surface and organize components by function
  
• Avoid mixing parts between spools, as tolerances are specific
  

If the manual references a Gresen valve but the machine has a Melroe unit, consult with a Bobcat dealer or hydraulic specialist to obtain the correct rebuild kit.
Recommended Parts and Inspection Points
During a rebuild, the following components should be replaced or inspected:

• O-rings: Replace all with high-quality Viton or Buna-N seals rated for hydraulic use
  
• Seals and packings: Inspect for hardening, cracking, or flattening
  
• Dust boots: Prevent contamination from entering the spool area
  
• Spool lands: Check for scoring or pitting—replace if damage is deep
  
• Valve bores: Inspect for oval wear or corrosion
  
• Springs: Test for tension and replace if fatigued or deformed
  
• Retaining clips and washers: Replace if bent or corroded
  

Use a light coating of hydraulic assembly grease during reinstallation to prevent dry startup and ease spool movement.
Field Anecdotes and Practical Advice
One technician in Minnesota shared that his 743 had stopped counting hours at 2,700 but likely had double that in real use. After noticing fluid squirting from the auxiliary spool and erratic tilt behavior, he removed the valve and discovered mismatched seals from a previous repair. Once rebuilt with the correct kit, the loader regained full hydraulic responsiveness.
Another operator emphasized the importance of checking the lift arm drift. If arms drop over time without input, it’s a clear sign of internal leakage—either in the valve or the cylinder seals. In his case, rebuilding the valve solved the issue without needing cylinder service.
Preventive Measures and Long-Term Reliability
To extend the life of the hydraulic system:

• Change hydraulic fluid and filters every 500 hours or annually
  
• Use fluid that meets Bobcat’s viscosity and additive specifications
  
• Keep the control valve area clean and free of debris
  
• Avoid holding hydraulic functions under load for extended periods
  
• Monitor for early signs of drift, noise, or fluid discoloration
  

For machines operating in cold climates, consider using low-temperature hydraulic fluid to reduce startup strain and prevent seal damage.
Conclusion
Rebuilding the hydraulic control valve on a Bobcat 743 is a rewarding but meticulous task. With careful identification, thorough cleaning, and proper seal replacement, operators can restore full functionality and avoid costly downtime. As these legacy machines continue to serve in farms, job sites, and rental fleets, maintaining their hydraulic heart is essential—and with the right approach, even a decades-old loader can run like new.