Terex TA27 Brake System Challenges and Solutions

[MikePhua]

The Terex Legacy and TA27 Development
Terex Corporation, founded in 1933, evolved from a division of General Motors into a global manufacturer of heavy equipment. By the 1990s, Terex had expanded its product line to include articulated dump trucks (ADTs), targeting mining, quarrying, and large-scale earthmoving operations. The TA27, introduced in the late 1990s, was part of the TA series that included models ranging from TA25 to TA40. These trucks were designed for high payload capacity, rugged terrain performance, and ease of maintenance.
The TA27 features a payload capacity of approximately 27 metric tons and is powered by a Detroit Diesel Series 60 engine producing around 350 horsepower. Its six-wheel drive configuration and articulated steering allow it to navigate rough terrain with agility. By the early 2000s, Terex had sold thousands of TA27 units globally, with strong adoption in North America, Europe, and Australia.
Brake System Architecture
The TA27 uses a dual braking system consisting of:

• Service brakes: hydraulically actuated wet disc brakes on all axles
  
• Parking brake: spring-applied, hydraulically released disc brake on the driveline
  
• Emergency brake: integrated with the parking brake system
  

Terminology Note: “Wet disc brakes” are enclosed in oil-filled housings, reducing wear and improving cooling. “Spring-applied, hydraulically released” means the brake engages by default and is released only when hydraulic pressure is applied.
The service brakes are controlled via a treadle valve, which modulates hydraulic pressure based on pedal input. The system includes accumulators to maintain pressure during engine-off conditions and a pressure converter to interface with air systems in some configurations.
Common Brake Issues and Diagnostics
Operators frequently report the following brake-related problems:

• Brake warning light activation during operation
  
• Soft or spongy pedal feel
  
• Delayed brake response
  
• Inability to release parking brake
  

These symptoms often stem from:

• Low hydraulic fluid levels
  
• Air ingress into the hydraulic lines
  
• Worn brake pads or discs
  
• Faulty treadle valve or pressure sensors
  

A quarry operator in Wales shared how his TA27’s brakes failed during a descent. The issue was traced to a ruptured accumulator diaphragm, which caused pressure loss. Replacing the accumulator and bleeding the system restored full braking function.
Hydraulic System Maintenance and Recommendations
To maintain optimal brake performance, operators should:

• Check hydraulic fluid levels daily
  
• Use ISO VG 46 hydraulic oil with anti-wear additives
  
• Replace brake fluid filters every 500 hours
  
• Bleed the system after any hose or component replacement
  

A technician in Alberta noted that using synthetic hydraulic fluid improved cold-weather performance, reducing brake lag during winter operations.
Parking Brake Troubleshooting
The parking brake on the TA27 is critical for safety during loading and unloading. Common issues include:

• Brake not releasing due to low hydraulic pressure
  
• Brake dragging during motion
  
• Warning light remaining on despite release
  

Solutions involve:

• Inspecting the hydraulic release solenoid
  
• Testing the pressure switch and wiring
  
• Replacing worn brake pads and checking caliper alignment
  

In 2018, a construction crew in Nevada retrofitted their TA27 with a manual override lever for the parking brake, allowing emergency release during hydraulic failure.
Brake Pad and Disc Wear Patterns
Wet disc brakes wear differently than dry systems. Indicators of wear include:

• Increased stopping distance
  
• Metallic grinding noise
  
• Uneven pad thickness
  

Operators should:

• Inspect brake discs every 1,000 hours
  
• Replace pads when thickness drops below 5 mm
  
• Use OEM or high-quality aftermarket components
  

A fleet manager in South Africa reported that switching to ceramic composite pads extended service intervals by 30%, reducing downtime.
Air System Integration and Valve Function
Some TA27 units include air-assisted braking components. Key parts include:

• Air drier to remove moisture
  
• Relay emergency valve to control air flow
  
• Pressure protection valve to isolate circuits
  

Failures in these components can cause:

• Brake lockup
  
• Inconsistent pedal feel
  
• Air leaks and compressor overload
  

Routine checks should include:

• Draining air tanks daily
  
• Replacing air drier cartridges every 1,000 hours
  
• Testing valve function with a pressure gauge
  

Operator Stories and Field Adaptations
A mining operator in Chile shared how his TA27’s brakes overheated during a long descent. He installed temperature sensors on the brake housings and used telemetry to monitor heat buildup. This allowed him to adjust descent speed and prevent failure.
Another operator in Finland added a secondary hydraulic reservoir to maintain brake pressure during extreme cold, improving safety during snow hauling.
Conclusion
The Terex TA27’s brake system is robust but demands regular attention to maintain safety and performance. From hydraulic fluid quality to accumulator integrity, each component plays a vital role. With proper diagnostics, preventive maintenance, and occasional upgrades, operators can ensure reliable braking even in the harshest conditions. The TA27 remains a workhorse in the ADT category, and its brake system—while complex—is manageable with diligence and expertise.