Rebuilding the Fan Blower Gearbox on the Bobcat 753 Skid Steer

[MikePhua]

The Bobcat 753 and Its Cooling System Architecture
The Bobcat 753 skid steer loader, introduced in the mid-1990s, was part of Bobcat’s push toward compact, high-performance machines for construction, landscaping, and agricultural use. Powered by a Kubota V2203 diesel engine, the 753 featured a belt-driven cooling fan mounted to a gearbox assembly that also supported the alternator and hydraulic pump. This fan blower gearbox is a critical component—transferring rotational energy from the engine to the cooling system while maintaining alignment and bearing integrity.
Over time, the gearbox can suffer from bearing wear, shaft misalignment, and seal degradation. Symptoms include excessive noise, vibration, overheating, and in severe cases, fan failure. Rebuilding the gearbox restores cooling efficiency and prevents collateral damage to the engine and hydraulic system.
Symptoms of Gearbox Failure and Early Warning Signs
Operators may notice:

• A high-pitched whine or grinding noise from the rear of the engine compartment
  
• Fan wobble or irregular rotation
  
• Hydraulic fluid overheating due to reduced airflow
  
• Belt slippage or premature wear
  
• Oil seepage around the gearbox housing
  

In one case, a Bobcat 753 began overheating during trenching work. Inspection revealed that the fan shaft had developed lateral play, causing the belt to misalign and the fan to lose efficiency. The gearbox bearings had worn unevenly, and the seals were leaking.
Disassembly and Component Inspection
To rebuild the gearbox:

• Disconnect the battery and remove the engine shroud
  
• Release belt tension and remove the fan assembly
  
• Unbolt the gearbox housing from the engine mount
  
• Extract the input and output shafts, noting bearing orientation
  
• Inspect bearings for pitting, scoring, or discoloration
  
• Check seals for hardening, cracking, or oil saturation
  

Use a bearing puller and seal driver to remove and install components. Clean all mating surfaces and apply thread locker to critical fasteners. One technician noted that the original bearings were open-style; replacing them with sealed units improved longevity and reduced contamination risk.
Recommended Replacement Parts and Specifications
Typical rebuild kits include:

• Input shaft bearing (6205 or equivalent)
  
• Output shaft bearing (6206 or equivalent)
  
• Oil seals (double-lip nitrile or Viton)
  
• Shaft bushings and spacers
  
• High-temperature grease (NLGI #2 lithium complex)
  

Torque specifications:

• Gearbox mounting bolts: 35–40 ft-lbs
  
• Fan hub bolts: 20–25 ft-lbs
  
• Belt tension: ½ inch deflection under 10 lbs pressure
  

Use OEM or high-quality aftermarket parts. Avoid generic bearings with unknown load ratings, as they may fail prematurely under vibration and heat.
Reassembly and Alignment Tips
During reassembly:

• Pack bearings with grease before installation
  
• Align shafts using a straightedge across the pulley faces
  
• Rotate the fan manually to check for smooth operation
  
• Reinstall the belt and adjust tension evenly
  
• Start the engine and monitor for noise, vibration, and temperature rise
  

One operator found that misalignment during reassembly caused belt squeal and premature wear. After realigning the pulleys and rechecking torque, the issue resolved.
Preventive Maintenance and Long-Term Reliability
To extend gearbox life:

• Inspect belt tension monthly
  
• Clean fan blades and housing to prevent debris buildup
  
• Monitor bearing noise during startup
  
• Replace seals every 1,500–2,000 hours or as needed
  
• Use a stethoscope to detect early bearing wear
  

For machines operating in dusty or abrasive environments, consider installing a fan shroud extension or debris deflector to reduce particulate intrusion.
Conclusion
Rebuilding the fan blower gearbox on the Bobcat 753 is a practical and rewarding task that restores cooling performance and protects critical systems. With careful disassembly, quality parts, and precise alignment, operators can eliminate noise, prevent overheating, and extend the life of their machine. In compact loaders, airflow is everything—and the gearbox is the silent hero behind it.