John Deere 644A Wheel Loader

The John Deere 644A Wheel Loader is a classic heavy-duty production loader built for aggregate, road building, forestry, and large-scale material handling. As one of Deere’s early articulated loaders, the 644A is known for its rugged frame, mechanical simplicity, and dependable drivetrain—making it a reliable machine even decades after production.

Its straightforward mechanical systems make field repairs and maintenance easier compared to modern electronically controlled equipment.

Engine & Power

• Engine: John Deere 6-404 diesel

• Displacement: 6.6L (404 cu in)

• Gross Power: ~125 hp

• Fuel System: Mechanical injection

• Emissions: Pre-emissions (no Tier requirements)

The naturally aspirated diesel engine delivers strong torque for stockpiling, truck loading, and quarry operations.

Transmission

• Type: Power Shift transmission

• Gears: 4 forward / 4 reverse

• Torque Converter: Heavy-duty

• Drive: 4WD articulated

The power shift system allows smooth shifting under load and dependable performance in demanding applications.

Hydraulic System

• System Type: Open-center hydraulic system

• Operating Pressure: ~2,500–2,800 psi

• Pump Type: Gear pump

• Lift & Tilt Cylinders: Dual-acting hydraulic cylinders

Common replacement components include:

• Hydraulic cylinder seal kits

• Hydraulic hoses and fittings

• Loader control valve components

Dimensions & Operating Weight

• Operating Weight: ~30,000–32,000 lb

• Bucket Capacity: 3.0–3.5 cu yd

• Hinge Pin Height: ~13 ft

• Wheelbase: ~10–11 ft

Performance Highlights

• Strong breakout force for heavy material

• Durable articulated frame design

• Wet-disc braking system

• Mechanical systems ideal for straightforward service

Common Maintenance Needs

• Engine oil and filter replacement

• Fuel and air filter service

• Hydraulic oil and filter changes

• Axle oil and brake inspection

Routine service items like filter kits and dependable brake components are essential to keep this classic loader productive.

Common Issues & Quick-Fix Solutions

1. Hydraulic Cylinder Leakage
Replace worn seals using quality hydraulic seal kits.

2. Transmission Slippage or Delayed Engagement
Check transmission fluid condition and inspect clutch packs and torque converter.

3. Brake Wear or Oil Contamination
Inspect wet brake system and replace worn seals promptly.

4. Articulation Joint Wear
Replace worn loader pins and bushings before structural damage occurs.

Pro Tips

• Grease articulation and pivot points daily during heavy production work.

• Monitor hydraulic hoses near articulation for abrasion.

• Address minor oil leaks quickly to protect the hydraulic pump and transmission.

Serial Number Information

The serial number plate is typically located on the right-hand side of the frame near the articulation joint or inside the operator platform area. Always verify your serial number before ordering parts to ensure proper fitment.