Fixing Hydraulic Reservoir Leaks on the CAT 944A

[MikePhua]

The CAT 944A and Its Hydraulic System Design
The Caterpillar 944A Traxcavator was introduced in the early 1960s as a wheel loader built for rugged earthmoving and industrial applications. With a robust frame, mechanical transmission, and open-center hydraulic system, the 944A became a staple in quarries, yards, and municipal fleets. Its hydraulic reservoir is mounted beneath the operator platform, sealed by a bolted bottom plate that allows access for cleaning and inspection.
Unlike modern sealed tanks with molded gaskets or welded seams, the 944A’s reservoir relies on a flat mating surface and a gasketed cover held by dozens of bolts. Over time, vibration, thermal cycling, and oil saturation degrade the gasket, leading to leaks that can soak the undercarriage and contaminate surrounding soil.
Identifying the Source of the Leak
Operators typically notice hydraulic fluid dripping from the perimeter of the reservoir’s bottom plate. The leak often appears uniform across multiple bolt holes, suggesting gasket failure rather than a cracked housing or loose fitting.
Common indicators:

• Oil staining around bolt heads
  
• Wet dirt buildup along the reservoir seam
  
• Drips forming after shutdown due to residual pressure
  
• No visible cracks or punctures in the tank body
  

In one case from rural Alberta, a loader parked overnight left a trail of hydraulic fluid across a gravel lot. Inspection revealed that the bottom plate gasket had extruded between bolts, allowing fluid to seep under gravity.
Choosing the Right Gasket Material
Replacing the gasket requires selecting a material that resists hydraulic oil, compresses evenly, and withstands bolt torque without extrusion. Options include:

• Nitrile rubber (NBR): Oil-resistant but prone to slipping and extrusion under uneven torque
  
• Gasket paper (cellulose-based): Compresses well, resists oil, and holds shape under bolt pressure
  
• Teflon rope: Used in some modern CAT tanks, but difficult to retrofit on older flat-flange designs
  
• Liquid gasket sealant: Effective for small covers but risky on large plates due to uneven curing and bolt pattern distortion
  

Recommended solution:

• Use 1mm black gasket paper rated for hydraulic oil
  
• Cut to match bolt pattern and reservoir profile
  
• Apply adhesive on one side to hold position during installation
  
• Use light sealant on the opposite face to prevent micro-leaks
  

A technician in Pennsylvania rebuilt a 944A reservoir using 1mm cellulose gasket paper and a thin layer of aviation-grade sealant. After torquing bolts in a crisscross pattern and retorquing after 24 hours, the leak was eliminated.
Bolt Torque and Gasket Compression
Overtightening bolts can distort the gasket and cause extrusion, especially with rubber-based materials. Underspec torque may allow fluid seepage. The 944A’s reservoir typically uses 5/8" or 3/4" bolts spaced evenly around the perimeter.
Best practices:

• Clean all bolt threads and mating surfaces
  
• Torque in stages: 30%, 60%, then full spec
  
• Use a crisscross pattern to distribute load
  
• Retorque after the gasket has taken a set (usually 24–48 hours)
  

In one fleet in Texas, a mechanic used a digital torque wrench and recorded each bolt’s final torque. This helped identify uneven compression zones and prevented future leaks.
Cleaning and Surface Preparation
Before installing the new gasket, the reservoir flange and bottom plate must be cleaned thoroughly. Residual oil, rust, or old gasket material can compromise the seal.
Steps:

• Drain hydraulic fluid and clean tank interior
  
• Scrape old gasket material with plastic or brass tools
  
• Use solvent to remove oil film from mating surfaces
  
• Inspect for pitting or warping—light sanding may be needed
  
• Avoid using abrasives that gouge the sealing surface
  

A contractor in Oregon used a borescope to inspect the inside of the reservoir for sludge and metal flakes. After flushing and resealing, the loader’s hydraulic performance improved noticeably.
Alternative Sealing Methods and Field Modifications
Some operators experiment with liquid gasket alone, especially when gasket material is unavailable. While this can work on small covers, it’s risky on large plates due to uneven curing and bolt pattern distortion.
Others have tried:

• Double-layer gaskets for uneven surfaces
  
• Reinforced rubber with embedded mesh
  
• Custom-cut cork gaskets (not recommended due to oil absorption and compression loss)
  

In one case from New Mexico, a loader was sealed using a nitrile gasket with aluminum backing. The material held under torque but failed after six months due to oil saturation and edge extrusion.
Preventive Maintenance and Monitoring
To prevent future leaks:

• Inspect reservoir bolts annually for torque and corrosion
  
• Replace gasket during major hydraulic service intervals
  
• Monitor fluid levels and look for unexplained drops
  
• Keep the reservoir vent clean to prevent pressure buildup
  

Adding a drip tray or absorbent mat under the reservoir can help detect early leaks and prevent environmental contamination.
Conclusion
Hydraulic reservoir leaks on the CAT 944A are often caused by aged gaskets and uneven bolt compression. With proper material selection, surface preparation, and torque discipline, operators can restore the seal and extend the life of this classic loader. Whether working in gravel pits or pasture land, a dry reservoir means cleaner operation, safer footing, and fewer surprises under the machine.