Restoring Braking Power on John Deere 544 and 644 Loaders

[MikePhua]

The Evolution of John Deere’s Mid-Size Wheel Loaders
John Deere’s 544 and 644 series wheel loaders have long been staples in construction, forestry, and municipal fleets. Introduced in the 1970s and continuously refined through the E, G, and later models, these machines offered a balance of power, maneuverability, and serviceability. The 544E and 644E, in particular, featured internal wet disc brakes, torque converter transmissions, and robust axles designed for heavy-duty use.
By the time the 644E was released, John Deere had incorporated twin brake pedals, dual accumulators, and separate hydraulic brake pumps, enhancing operator control and redundancy. These loaders were built to last, with many units surpassing 20,000 hours in service. However, brake system degradation is inevitable, especially in machines used for hauling, snow removal, or quarry work.
Understanding Internal Wet Disc Brakes
Wet disc brakes are sealed within the axle housing and operate in hydraulic fluid, offering superior cooling and reduced wear compared to dry systems. They consist of alternating steel and friction discs compressed by hydraulic pistons when the brake pedal is applied.
Terminology clarification:

• Wet Disc Brake: A brake system where friction discs operate submerged in hydraulic oil, reducing heat and wear.
  
• Accumulator: A pressurized vessel that stores hydraulic energy for brake application.
  
• Brake Pump: A dedicated hydraulic pump supplying pressure to the brake circuit, separate from steering or implement hydraulics.
  

Symptoms of Brake Failure and Initial Inspection
In one case, a 644E loader exhibited nearly non-functional brakes. The rear brakes were plugged off, and the front brakes were worn to metal-on-metal contact. A brake warning light was illuminated on the dash, suggesting low pressure or accumulator failure.
Initial steps included:

• Inspecting fluid levels in axle housings
  
• Checking for overfilled axles, which may indicate leaking brake piston seals
  
• Verifying accumulator charge and pressure switch function
  
• Examining the brake pump mounted behind the main hydraulic pump
  

A high fluid level in the axle can signal internal seal failure, allowing brake fluid to leak into the axle housing. This not only compromises braking but also risks contaminating gear oil and damaging bearings.
Disassembly Strategy and Axle Handling
Servicing internal brakes requires partial axle disassembly. The rear axle on the 644E is center-mounted on trunnions, allowing one side to be serviced at a time. The front axle can be removed entirely by unbolting and jacking the frame.
Recommendations for safe disassembly:

• Use bottle jacks rated for at least 5 tons
  
• Fabricate a wheeled cradle to support and roll the axle assembly
  
• Remove wheels, driveshaft, and brake lines before accessing the brake housing
  
• Expect axle assemblies to weigh over 2,500 lbs—ensure lifting equipment is rated accordingly
  

A technician in Massachusetts used a Kubota loader with 3,000 lb forks to assist in axle handling, supplemented by a custom dolly for maneuvering the brake housing.
Repairing the Parking Brake with Ingenuity
The parking brake on this loader was severely worn, with the friction surface completely degraded. Instead of sourcing expensive OEM parts, the technician used a creative approach:

• Removed old friction material with an air chisel
  
• Smoothed the surface with a belt sander and lathe
  
• Cut new friction pads from industrial sheet stock
  
• Bonded them using marine-grade epoxy resistant to oil and fuel
  
• Clamped and cured for 24 hours, then sanded for clearance
  

The result was a functional parking brake capable of holding the loader on a slope. This kind of field ingenuity is common in rural operations where downtime is costly and parts are scarce.
Brake Pump Diagnosis and Replacement Options
The 644E uses a dedicated piston pump for the brake circuit. If both pedals fail to generate pressure, and accumulators are charged, the pump may be at fault. Before replacing:

• Test pump output pressure with a hydraulic gauge
  
• Inspect for shaft wear or internal scoring
  
• Consider rebuilding at a local hydraulic shop if parts are available
  

Replacement pumps are available through aftermarket suppliers, but rebuilding can save 30–50% of the cost. Ensure compatibility with the loader’s serial number and verify flow rate and pressure specs.
Preventive Maintenance and Long-Term Solutions
To extend brake system life:

• Change axle oil every 1,000 hours and inspect for contamination
  
• Test accumulator pressure quarterly
  
• Replace brake fluid filters annually
  
• Monitor pedal feel and response—sponginess may indicate air or seal failure
  
• Avoid prolonged braking on steep grades to reduce heat buildup
  

For loaders exceeding 20,000 hours, consider a full brake system overhaul, including seals, discs, and pump rebuild. This investment can restore full stopping power and prevent costly axle damage.
Conclusion
Servicing the brakes on a John Deere 544 or 644 loader is a heavy but manageable task with the right tools and planning. Whether rebuilding the parking brake with epoxy or fabricating axle cradles for safe removal, field repairs often blend mechanical skill with creativity. With proper diagnostics and preventive care, these loaders can continue operating safely and reliably—even after decades of hard use.