FAW Brake Line: Deconstructing the 56 Critical Components That Ensure Your Safety

Welcome to this critical technical guide on the FAW Brake Line system (Assembly 539). This is the complete, multi-circuit, high-pressure pneumatic braking and control system for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This assembly is arguably the most critical safety system on the entire vehicle.

The FAW Brake Line is not a single part, but a complex “logic” network of valves, hoses, pipes, sensors, and brackets. Its function is to take the compressed air from the air compressor and distribute it on demand to the service brakes (foot pedal), parking brakes (hand valve), and trailer brake circuits. This “air-over-mechanical” logic provides the immense stopping power required for a fully-loaded tractor-trailer.

This in-depth guide is an essential resource for professional chassis technicians and parts specialists. We will deconstruct the entire FAW Brake Line system into its 56 serviceable components, including the ‘Air dryer’ (3511020-81W-C00), ‘Air processing unit’ (3515020-81W-C00), ‘ABS solenoid valve’ (3550310-50A), and all the critical hoses, fittings, and brackets that make the system function.

The “Logic” of a Pneumatic FAW Brake Line

The FAW Brake Line system is pneumatic (air-powered), not hydraulic like a passenger car. This is a critical design “logic” for heavy-duty trucks. First, air pressure provides far more stopping force than hydraulic pressure can, which is essential for a 40-ton vehicle. Second, the system is “fail-safe.” A hydraulic leak results in total brake failure. A leak in a pneumatic FAW Brake Line will cause the spring-brakes (parking brakes) to automatically engage, safely stopping the truck.

This logic is managed by two core components:

• **’Air dryer assembly’ (3511020-81W-C00):** This is the “lung” of the FAW Brake Line. It takes hot, wet air from the compressor and “dries” it by passing it through a desiccant filter. This is a critical first step, as any moisture in the system would freeze in cold weather, blocking the valves and causing total brake failure.
• **’Air processing unit (APU)’ (3515020-81W-C00):** This is the “brain.” It is a central distribution manifold. It takes the clean, dry air and splits it into multiple, redundant circuits (e.g., front brakes, rear brakes, trailer brakes, parking brake). This ensures that a failure in one FAW Brake Line circuit (like a blown hose) will not cause a total loss of stopping power.

The “Electronic Logic”: ABS and Solenoids

The modern FAW Brake Line system is not just pneumatic; it is electro-pneumatic. The ‘Anti-lock brake solenoid valve assembly’ (3550310-50A) is the electronic interface. This valve block receives high-speed commands (hundreds of times per second) from the truck’s ABS computer.

When the driver panic-stops and a wheel begins to lock up (as detected by the wheel speed sensors), the ABS computer instantly commands this solenoid. The solenoid then rapidly “pumps” the air pressure to that specific wheel’s brake chamber, releasing and reapplying the brake much faster than any human could. This is the “anti-lock” logic that allows the driver to maintain steering control during a panic stop.

This system also includes the ‘Hand brake valve with protective cover assy’ (3508015-91W-C00) and ‘Foot brake valve & clutch plate assy’ (3504020-91W). These are the driver’s primary inputs, translating foot and hand movement into proportional air pressure signals. The FAW Brake Line is a complex integration of mechanical, pneumatic, and electronic logic.

The “Lines”: Hoses, Pipes, and Bundles

The “Line” part of the FAW Brake Line keyword refers to the physical “arteries” that carry the compressed air. This is a combination of rigid pipes and flexible hoses.

**Hoses:** The ‘Brake flexible hose-front brake’ (3506030-60A & 3506040-1051) and ‘Control flexible hose-front brake’ (3506040-1051) are used at the “wheel ends.” This is a critical “logic” choice, as these flexible, wire-braided hoses must be able to withstand 120+ PSI of pressure while constantly flexing and turning with the front steering wheels. A cracked or abraded hose is a common failure point in any FAW Brake Line system.

**Pipes & Bundles:** The ‘Front air pipe assy’ (3506205-91W), ‘Pipe bundle assy’ (3506100-92W), and ‘Air compressor air pipe assy’ (3506210A91W) are the main rigid lines. These are typically pre-bent nylon or steel tubes that run along the chassis frame. They are bundled together for protection and ease of installation. A “bundle” is a key part of the FAW Brake Line logic, as it keeps the critical, color-coded lines organized and protected from road debris.

Brackets, Fittings, and Support Structure

A FAW Brake Line system is under constant vibration. Its “logic” requires that it be rigidly mounted to the chassis to prevent fatigue and failure. This parts list details an extensive support system:

• ‘Front pipe bundle bracket’ (3506038-91W, 3506430-91W)
• ‘Bracket-hand brake valve’ (3522012-91W)
• ‘Bracket-air processing unit’ (3515021-91W)
• ‘Transition bracket-air storage module’ (3513824-91W)
• ‘Main wiring harness bracket’ (3724426-68V) (shared bracket)

The ‘Fittings’ are the dozens of small, but critical, connectors. This includes ‘Grommets’ (3506204-50A), ‘Multi-way joints’ (3506404-50A), ‘Plugs’ (3506407-1500), and numerous ‘Sealing rings’ (3515416-81W-C00, 3513403-1500, 3506413-1500, etc.). Each one of these is a potential leak point. The “logic” of the FAW Brake Line is to use high-quality, O-ring-sealed (grommet-type) fittings to ensure a leak-free system. A leaking fitting is a critical, “vehicle-down” failure.

The entire FAW Brake Line is fastened with hundreds of high-tensile, vibration-resistant fasteners, including ‘Hex flange bolts’ (Q1841445T) and ‘Hex head flange lock nuts’ (CQ32614), to ensure total system integrity.

FAW Brake Line Parts List (1/2)

The following table provides the first part of the detailed breakdown for the FAW Brake Line (539) diagram for the FAW CA4251P66K24T1A3E5 tractor.

FAW Brake Line Parts List (2/2)

This table details the remaining components for the FAW Brake Line (539) diagram.

Technical Specifications and Assembly Context

The specifications for the FAW Brake Line system are defined by its function as a complete, multi-circuit, high-pressure pneumatic system. The FAW Brake Line is a safety-critical system for vehicle control.