Restoring Brake Function on a John Deere 310A Backhoe

[MikePhua]

The JD 310A and Its Hydraulic Brake System
The John Deere 310A backhoe loader was introduced in the late 1970s as part of Deere’s push into the compact construction equipment market. Built with a naturally aspirated 4-cylinder diesel engine and a mechanical transmission, the 310A was designed for reliability and ease of service. Its braking system, however, has proven to be a point of failure in aging units. The 310A uses a hydraulic brake system with dual pedals, each controlling a separate rear wheel brake. Fluid is supplied from the transmission reservoir, routed through a valve block beneath the pedals, and actuated by internal pistons and check valves.
Terminology annotation:
- Brake valve block: A cast hydraulic manifold beneath the pedals that regulates fluid flow to the brake cylinders.
- Check valve: A one-way valve that prevents backflow and maintains pressure in the brake circuit.
- Bleeder screw: A valve used to release air from hydraulic lines during brake bleeding.
- Transmission reservoir: The shared fluid tank supplying hydraulic oil to multiple systems, including brakes.
Symptoms of Brake Failure and Initial Diagnosis
Operators have reported sudden loss of braking, with both pedals dropping to the floor and no resistance. In one case, the backhoe had sat idle for several months before the brakes failed completely. Attempts to bleed the system yielded little to no fluid, and only air escaped when the pedal was depressed. This suggests either a blockage in the supply line or internal failure within the valve block.
A common mistake during bleeding is leaving the bleeder valve open while pumping the pedal. The correct procedure is:

• Open bleeder
  
• Depress and hold pedal
  
• Close bleeder
  
• Release pedal
  
• Repeat until fluid flows steadily
  

Using a clear hose from the bleeder to a catch container helps monitor air bubbles and fluid volume.
Disassembly and Inspection of the Valve Block
To investigate further, the operator removed the brake valve block and discovered oil flowing freely from the supply port when the engine was running. This confirmed that fluid was reaching the block, but not passing through it. Upon disassembly, the internal pistons showed minor pitting, and one check valve was dislodged by compressed air. The block contains multiple plugs, each retaining springs, check balls, and O-rings. These components are critical for maintaining pressure and directing flow.
Recommendations for inspection:

• Remove all plugs carefully, expecting spring-loaded components
  
• Clean passages with solvent and compressed air
  
• Replace worn or pitted pistons and O-rings
  
• Verify check valve orientation and seating
  
• Use a manual or diagram to identify internal flow paths
  

One operator noted that the check valve plug was difficult to remove and considered welding a nut to extract it. Eventually, it was punched out from below without damage.
Brake Line Replacement and Flare Type Identification
During reassembly, the original brake lines were found to be brittle and cracked. Replacing them required identifying the correct flare type. The fittings appeared to use a double flare, common in automotive and light equipment hydraulic systems. Bubble flares are less typical in Deere equipment of this era.
Recommendations:

• Use a double flare tool with SAE fittings
  
• Match line diameter to original spec (usually 3/16" or 1/4")
  
• Replace caps and elbows with compatible hydraulic-rated components
  
• Avoid overtightening to prevent thread damage
  

Bleeding Challenges and Pressure Switch Confusion
On the right side of the axle housing, the bleeder fitting was replaced with a pressure switch, possibly installed by a previous owner. This created confusion during bleeding, as the switch lacked a standard valve. The operator resorted to loosening the elbow fitting to release air. While effective, this method is imprecise and risks damaging threads.
Solutions:

• Replace pressure switch with a proper bleeder screw
  
• Install a remote bleeder kit for easier access
  
• Use a socket and vice grips for tight fittings
  
• Bleed with engine running to ensure fluid pressure
  

Field Anecdotes and Shared Experience
Another operator working out of state reported identical symptoms and planned to remove his valve block for inspection. He confirmed that the service manual shows springs and check balls behind nearly every plug. This reinforces the need for caution and documentation during disassembly.
In one case, the left brake was successfully bled after line replacement, suggesting that the failure was due to a combination of internal blockage and broken lines. The right side remained problematic due to the non-standard fitting.
Conclusion
Restoring brake function on a John Deere 310A requires a methodical approach: verifying fluid supply, inspecting the valve block, replacing damaged lines, and bleeding the system correctly. The hydraulic brake design is simple but sensitive to contamination, wear, and improper bleeding technique. With patience and attention to detail, even a decades-old backhoe can regain safe stopping power. For operators maintaining legacy equipment, understanding the internal mechanics of the brake system is essential—not just for repairs, but for preserving the machine’s working life.