Rebuilding Tilt Cylinders on the Caterpillar 955 12A Track Loader

[MikePhua]

The 955 12A and Its Hydraulic Architecture
The Caterpillar 955 12A track loader was introduced in the late 1950s as part of Caterpillar’s push into mid-size crawler loaders. With a robust undercarriage, torque converter transmission, and hydraulic tilt and lift cylinders, the 955 12A became a staple in construction, logging, and land clearing. Thousands of units were sold globally, and many remain in service today due to their mechanical simplicity and rugged build.
One of the key components in the 955’s hydraulic system is the tilt cylinder, which controls the angle of the bucket. These cylinders are subject to constant stress, especially during grading and material handling. Over time, seals degrade, rods wear, and internal components loosen—necessitating a full rebuild to restore performance.
Identifying Seal Kits and Sourcing Parts
The tilt cylinders on the 955 12A typically feature a 5-inch bore and a 2-inch rod. Rebuilding requires a complete seal kit, including:

• Rod wiper
  
• Rod seal
  
• Piston seal
  
• Wear rings
  
• O-rings and backup rings
  

Aftermarket suppliers such as Hercules and Baum Hydraulics offer seal kits for vintage Caterpillar equipment. For the 12A series, Hercules catalog part BD-507166 is commonly referenced, though measurements should be confirmed before ordering. Some suppliers may require the cylinder’s serial number or physical dimensions to match the correct kit.
Operators in Canada and the U.S. have reported success sourcing parts from regional distributors, though shipping and availability can vary. Keeping a physical catalog or requesting updated listings annually helps ensure access to legacy components.
Disassembly Challenges and Torque Requirements
One of the most daunting aspects of rebuilding these cylinders is removing the piston nut. These nuts are torqued to extreme levels—often exceeding 680 ft-lbs—and may be secured with thread locker or staking. Without the proper tools, removal can be nearly impossible.
Recommended tools and techniques include:

• Heavy-duty bench vise or rod clamp
  
• 4-foot pipe wrench or socket with cheater bar
  
• Loader bucket or hydraulic press for applied force
  
• Marking the nut position before removal for reassembly reference
  
• Using Loctite or equivalent thread sealant during reinstallation
  

Some mechanics fabricate custom benches or embed steel pipes in concrete to create a stable platform for disassembly. This approach allows for controlled torque application and reduces the risk of rod damage.
Anecdote from Virginia
A veteran mechanic in Virginia shared his method for removing stubborn piston nuts. He clamps the rod in a service truck vise and uses the loader’s bucket to apply downward pressure on a pipe wrench. This technique has proven effective even on cylinders untouched for decades. He’s now considering installing a permanent ground-level fixture to streamline the process.
Rebuild Tips and Best Practices
Once disassembled, the cylinder should be inspected for:

• Rod scoring or pitting
  
• Barrel wear or corrosion
  
• Piston ring groove damage
  
• End cap thread integrity
  

If the rod is damaged, it may need to be re-chromed or replaced. Minor scoring can be polished out, but deep gouges compromise seal life. The barrel should be honed if internal wear is present, and all components cleaned thoroughly before reassembly.
During reassembly:

• Lubricate seals with hydraulic oil or assembly grease
  
• Align wear rings carefully to prevent pinching
  
• Torque the piston nut to spec and verify alignment marks
  
• Pressure test the cylinder before reinstalling on the machine
  

Operators should also flush the hydraulic system and replace fluid to prevent contamination from old seals or debris.
Preserving the Legacy of the 955 Series
Caterpillar’s 955 series was produced for over two decades, with the 12A variant representing a transitional model between cable-operated and fully hydraulic loaders. Its popularity stemmed from reliability, ease of maintenance, and parts interchangeability. While newer machines offer electronic controls and emissions compliance, the 955 remains a favorite among restoration enthusiasts and small contractors.
Caterpillar, founded in 1925, has built a reputation for durable earthmoving equipment. The 955’s continued presence in the field is a testament to that legacy. Rebuilding tilt cylinders is part of preserving these machines and ensuring they remain productive for years to come.
Conclusion
Rebuilding the tilt cylinders on a Caterpillar 955 12A is a challenging but achievable task for mechanically inclined operators. With the right tools, accurate measurements, and quality seal kits, the process can restore hydraulic performance and extend the life of this iconic track loader. Whether in a rural shop or a professional rebuild facility, the effort pays off in reliability and pride of ownership. The 955 may be vintage, but its iron still earns its keep.