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CAT 950B Loader Overview
The Caterpillar 950B is a mid-size wheel loader introduced in the 1980s, designed for aggregate handling, stockpile work, and general construction. Powered by a CAT 3204 turbocharged diesel engine producing approximately 150 horsepower, the 950B features an air-over-hydraulic braking system and a torque converter transmission. Caterpillar, founded in 1925, has sold tens of thousands of 950-series loaders globally, and the B variant remains common in legacy fleets due to its mechanical simplicity and robust frame.
The braking system on the 950B includes dual treadle valves, air tanks, master cylinders, and axle-mounted service brakes. Each axle operates on an independent hydraulic circuit, fed by air-actuated master cylinders. This design ensures partial braking capability even if one circuit fails.
Terminology Notes
Operators report that the brakes on a 950B loader work flawlessly if the pedal is fully depressed and released. However, if the operator hovers or lightly rests on the pedal, the brakes may fail intermittently—even when the air tank is fully charged. This behavior is especially common with unfamiliar drivers, such as independent truckers loading material.
The left treadle valve was replaced, and the air compressor was serviced due to oil loss, but the issue persisted. The loader’s clutch disconnect feature was disabled, and the left pedal was confirmed to be non-neutralizing. The right pedal had not been inspected.
Common Causes of Intermittent Brake Failure
In New Hampshire, a fleet operator noted that brakes worked perfectly when the pedal was fully pressed and released. However, truck drivers unfamiliar with the loader often hovered on the pedal, causing brake loss. After inspecting the brake system operation diagram, he confirmed that each axle had its own master cylinder and that partial pedal application failed to generate adequate pressure.
In Manitoba, a technician found that the right treadle valve had never been serviced. Once replaced, brake consistency improved. He emphasized that both pedals must be understood and maintained, especially in older CAT loaders with dual-valve configurations.
Recommendations for Technicians and Owners
Intermittent brake failure on the CAT 950B loader often stems from master cylinder wear, treadle valve confusion, and operator technique. With dual braking circuits and air-over-hydraulic actuation, consistent pedal behavior and component maintenance are critical. By addressing both mechanical and human factors, owners can restore reliable braking and extend the life of this classic workhorse.
The Caterpillar 950B is a mid-size wheel loader introduced in the 1980s, designed for aggregate handling, stockpile work, and general construction. Powered by a CAT 3204 turbocharged diesel engine producing approximately 150 horsepower, the 950B features an air-over-hydraulic braking system and a torque converter transmission. Caterpillar, founded in 1925, has sold tens of thousands of 950-series loaders globally, and the B variant remains common in legacy fleets due to its mechanical simplicity and robust frame.
The braking system on the 950B includes dual treadle valves, air tanks, master cylinders, and axle-mounted service brakes. Each axle operates on an independent hydraulic circuit, fed by air-actuated master cylinders. This design ensures partial braking capability even if one circuit fails.
Terminology Notes
- Treadle Valve: A foot-operated valve that converts pedal movement into air pressure for brake actuation.
- Master Cylinder: A hydraulic piston assembly that converts air pressure into hydraulic force for brake engagement.
- Clutch Disconnect: A feature that disengages the transmission when braking, reducing load on the driveline.
- Neutralizer: A system that stalls the torque converter or disengages drive during braking or dumping.
Operators report that the brakes on a 950B loader work flawlessly if the pedal is fully depressed and released. However, if the operator hovers or lightly rests on the pedal, the brakes may fail intermittently—even when the air tank is fully charged. This behavior is especially common with unfamiliar drivers, such as independent truckers loading material.
The left treadle valve was replaced, and the air compressor was serviced due to oil loss, but the issue persisted. The loader’s clutch disconnect feature was disabled, and the left pedal was confirmed to be non-neutralizing. The right pedal had not been inspected.
Common Causes of Intermittent Brake Failure
- Sticking Master Cylinder Pistons
Over time, the pistons inside the master cylinders may stick due to corrosion, seal degradation, or contamination. This can prevent full hydraulic pressure from reaching the brakes, especially during partial pedal application.
- Collapsed Hydraulic Lines
Internal collapse or restriction in the brake lines can cause inconsistent fluid flow, leading to delayed or failed brake engagement.
- Incorrect Treadle Valve Function
The 950B uses two treadle valves—one with clutch disconnect and one without. If the wrong valve is replaced or misadjusted, the system may not deliver consistent air pressure.
- Driver Technique and Pedal Behavior
Hovering on the pedal without full depression may not trigger sufficient air pressure to actuate the master cylinders. This is compounded by unfamiliarity with dual-pedal systems.
- Transmission Neutralizer Deactivation
Without neutralizer engagement, the torque converter remains loaded during braking, increasing stopping distance and reducing brake effectiveness.
In New Hampshire, a fleet operator noted that brakes worked perfectly when the pedal was fully pressed and released. However, truck drivers unfamiliar with the loader often hovered on the pedal, causing brake loss. After inspecting the brake system operation diagram, he confirmed that each axle had its own master cylinder and that partial pedal application failed to generate adequate pressure.
In Manitoba, a technician found that the right treadle valve had never been serviced. Once replaced, brake consistency improved. He emphasized that both pedals must be understood and maintained, especially in older CAT loaders with dual-valve configurations.
Recommendations for Technicians and Owners
- Replace Both Master Cylinders: Prevent sticking and ensure balanced braking across axles.
- Inspect and Replace Hydraulic Lines: Look for internal collapse or contamination.
- Verify Treadle Valve Functionality: Ensure correct valve is installed and adjusted.
- Educate Operators on Pedal Use: Full depression and release are essential for proper brake actuation.
- Consider Reactivating Neutralizer: Reduces driveline load during braking and improves safety.
Intermittent brake failure on the CAT 950B loader often stems from master cylinder wear, treadle valve confusion, and operator technique. With dual braking circuits and air-over-hydraulic actuation, consistent pedal behavior and component maintenance are critical. By addressing both mechanical and human factors, owners can restore reliable braking and extend the life of this classic workhorse.
