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Overview of the G960 Service Brake System
The G960 motor grader, part of a line including models G930, G940, G946, is equipped with advanced hydraulic power-assisted service brakes designed for heavy-duty operation and reliable stopping power. The service brakes are oil-disc type, hydraulically actuated on all four tandem drive wheels, fully sealed, and maintenance-free, providing fade-resistant braking that meets stringent industry standards such as SAE J/EN ISO 3450:1996. The braking system incorporates crossover dual circuits to ensure braking effectiveness and safety even if one circuit fails.
The braking power is boosted hydraulically by an external gear-type pump mounted on the transmission, supplying oil via an open-center circuit at a regulated pressure of approximately 10 MPa (103 bar/1500 psi). The system includes a hydraulic power booster with an integrated electric backup pump. This electric pump automatically activates if the engine stalls or hydraulic pressure is lost to bring the vehicle to a safe stop or maintain braking on slopes until parking brakes engage.
The parking brake itself is a spring-applied, hydraulically released multi-disc brake housed inside the rear axle's final drive. It also has an accumulator that stores system pressure to keep the brakes released for about twenty minutes after system pressure loss, providing added operational safety.
Symptoms and Meaning of Service Brake Circuit Failure
The error message “Service Brake Circuit Failure” typically indicates a fault detected within one or both of the dual hydraulic circuits responsible for operating the service brakes. Since the braking system has two independent hydraulic circuits operating diagonally across the wheels, failure of a single circuit triggers a differential pressure switch. This switch then illuminates a warning lamp accompanied by an audible alarm, alerting the operator to a potential safety hazard.
This failure could mean:
Troubleshooting Starting Points
When diagnosing a “Service Brake Circuit Failure” message, a systematic approach is essential:
The oil disc brake assembly uses a friction pack consisting of alternating organic-faced friction discs and steel reaction plates. The discs attach to a splined hub on the axle shaft, while the reaction plates are splined inside the brake housing. When hydraulic pressure moves the piston, it compresses the friction pack to generate braking force. The number of discs varies by model:
Safety and Operational Considerations
When the system detects a service brake failure, it automatically engages the backup electric pump to ensure some braking assistance continues. The design ensures the vehicle can be safely stopped even during failure scenarios. Operators should not ignore warning signals, as continued operation with compromised brakes increases accident risk.
Tests to verify the functionality of the service brakes include rolling the grader down a 20% grade and applying brakes at low speed to ensure abrupt stopping ability.
A Related Story from Field Experience
In a case documented in the Alberta region, an operator encountered the “Service Brake Circuit Failure” warning on a G960. Initial manual search for troubleshooting guidance yielded sparse information, causing concern about safety and operation. The operator’s first step was a thorough hydraulic fluid inspection and line check, revealing a small leak at a fitting. After the leak repair and system bleeding, the error cleared, showing the importance of simple checks before extensive repairs.
Development and Importance of the G960 Braking System
The Volvo G960 motor grader was developed as a powerful, reliable machine for heavy grading, earthmoving, and construction tasks. First introduced as part of the G900 series, it emphasizes operator safety and system redundancy in hydraulic components. The choice of hydraulically actuated oil disc brakes reflects advances in braking technology, providing fade resistance and sealed units requiring minimal maintenance—essential for harsh terrain and heavy loads. Volvo’s commitment to asbestos-free components also marks environmental and health considerations in design.
The G960 motor grader series has been sold worldwide with strong demand due to its balance of power, fuel efficiency, and advanced control systems, including braking and steering. Its hydraulic brake system ensures dependable stopping power critical for safe operation in varied worksite conditions.
Glossary
The G960 motor grader, part of a line including models G930, G940, G946, is equipped with advanced hydraulic power-assisted service brakes designed for heavy-duty operation and reliable stopping power. The service brakes are oil-disc type, hydraulically actuated on all four tandem drive wheels, fully sealed, and maintenance-free, providing fade-resistant braking that meets stringent industry standards such as SAE J/EN ISO 3450:1996. The braking system incorporates crossover dual circuits to ensure braking effectiveness and safety even if one circuit fails.
The braking power is boosted hydraulically by an external gear-type pump mounted on the transmission, supplying oil via an open-center circuit at a regulated pressure of approximately 10 MPa (103 bar/1500 psi). The system includes a hydraulic power booster with an integrated electric backup pump. This electric pump automatically activates if the engine stalls or hydraulic pressure is lost to bring the vehicle to a safe stop or maintain braking on slopes until parking brakes engage.
The parking brake itself is a spring-applied, hydraulically released multi-disc brake housed inside the rear axle's final drive. It also has an accumulator that stores system pressure to keep the brakes released for about twenty minutes after system pressure loss, providing added operational safety.
Symptoms and Meaning of Service Brake Circuit Failure
The error message “Service Brake Circuit Failure” typically indicates a fault detected within one or both of the dual hydraulic circuits responsible for operating the service brakes. Since the braking system has two independent hydraulic circuits operating diagonally across the wheels, failure of a single circuit triggers a differential pressure switch. This switch then illuminates a warning lamp accompanied by an audible alarm, alerting the operator to a potential safety hazard.
This failure could mean:
- Loss or significant drop of hydraulic pressure in one circuit.
- Blockage or leakage in brake lines.
- Malfunction or failure of the gear-type hydraulic pump supplying the booster.
- Electrical issues with the backup pump or the pressure switch system.
- Mechanical issues like damaged brake discs, pistons, or seals.
Troubleshooting Starting Points
When diagnosing a “Service Brake Circuit Failure” message, a systematic approach is essential:
- Check Hydraulic Fluid Level and Condition: Low fluid or contaminated oil can cause pressure drops or blockages. Use the dipstick on the tandem case to verify the oil level and look for darkening or sludge.
- Inspect Hydraulic Lines and Fittings: Look for leaks, cracks, or loose fittings within the brake and booster circuits.
- Test Hydraulic Pump Operation: The externally mounted gear pump pulls oil from the transmission sump; it must deliver consistent pressure (around 103 bar). Failure or worn pump components need replacement.
- Examine Backup Electric Pump Function: This pump activates when pressure is lost. Electrical connections, fuse integrity, and motor operation require verification.
- Operate Brake Pedal and Monitor Differential Pressure Switch: Confirm the pressure switch is functioning accurately; it controls the warning system and backup pump engagement.
- Inspect Brake Components: Although the oil-disc service brakes are modular and maintenance-free, mechanical wear on friction discs or piston seals could cause hydraulic leaks or pressure issues.
- Check for Diagnostic Codes: Some machines have onboard diagnostics providing fault codes that narrow the cause.
The oil disc brake assembly uses a friction pack consisting of alternating organic-faced friction discs and steel reaction plates. The discs attach to a splined hub on the axle shaft, while the reaction plates are splined inside the brake housing. When hydraulic pressure moves the piston, it compresses the friction pack to generate braking force. The number of discs varies by model:
- G930: 3 discs / 4 plates
- G940, G946, G960: 4 discs / 5 plates
- G970 and up: 5 discs / 6 plates
Safety and Operational Considerations
When the system detects a service brake failure, it automatically engages the backup electric pump to ensure some braking assistance continues. The design ensures the vehicle can be safely stopped even during failure scenarios. Operators should not ignore warning signals, as continued operation with compromised brakes increases accident risk.
Tests to verify the functionality of the service brakes include rolling the grader down a 20% grade and applying brakes at low speed to ensure abrupt stopping ability.
A Related Story from Field Experience
In a case documented in the Alberta region, an operator encountered the “Service Brake Circuit Failure” warning on a G960. Initial manual search for troubleshooting guidance yielded sparse information, causing concern about safety and operation. The operator’s first step was a thorough hydraulic fluid inspection and line check, revealing a small leak at a fitting. After the leak repair and system bleeding, the error cleared, showing the importance of simple checks before extensive repairs.
Development and Importance of the G960 Braking System
The Volvo G960 motor grader was developed as a powerful, reliable machine for heavy grading, earthmoving, and construction tasks. First introduced as part of the G900 series, it emphasizes operator safety and system redundancy in hydraulic components. The choice of hydraulically actuated oil disc brakes reflects advances in braking technology, providing fade resistance and sealed units requiring minimal maintenance—essential for harsh terrain and heavy loads. Volvo’s commitment to asbestos-free components also marks environmental and health considerations in design.
The G960 motor grader series has been sold worldwide with strong demand due to its balance of power, fuel efficiency, and advanced control systems, including braking and steering. Its hydraulic brake system ensures dependable stopping power critical for safe operation in varied worksite conditions.
Glossary
- Hydraulic Power Booster: Device using hydraulic pressure to increase braking force applied by the driver.
- Oil Disc Brake: A brake type using discs and hydraulic pressure with friction material to create stopping force.
- Differential Pressure Switch: A sensor detecting pressure difference between two brake circuits to signal faults.
- Gear-Type Hydraulic Pump: A pump using interlocking gears to push hydraulic fluid at a set pressure.
- Accumulator: A hydraulic component storing pressurized fluid to maintain system pressure temporarily after pump loss.
- Friction Disc: Component with friction material that clamps against plates to generate braking force.
- Backup Electric Pump: An electric pump supplying hydraulic pressure when the main pump or engine fails.
