FAW Main Box Left-Lower Centre Shaft Assembly: Inside The 14 Critical Components That Drive It

Welcome to this critical technical guide on the FAW Main Box Left-Lower Centre Shaft Assembly (الجزء لا. 1701271-A2V). This is a complete, load-bearing gear and shaft set for the main gearbox of the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor.

ال FAW Main Box Left-Lower Centre Shaft Assembly, also known as a “counter-shaft,” is the literal workhorse of the transmission. This gearbox uses a “twin-countershaft” design, meaning it splits the engine’s torque between this shaft and an “Upper Right” shaft. This design is the key to its heavy-duty torque capacity.

This in-depth guide is an essential resource for professional transmission technicians and parts specialists. We will deconstruct the entire FAW Main Box Left-Lower Centre Shaft Assembly into its 14 serviceable components, including the main shaft, all of its drive gears, the critical bearings, and all associated locking hardware.

ال “Twin-Shaft” Logic Explained

The main gearbox of this FAW tractor uses a **twin-countershaft** (أو “twin-shaft”) design. This is the gold standard for heavy-duty applications. Instead of one large countershaft handling 100% of the engine’s torque, the load is “split” 50/50 between two smaller, identical countershafts.

هذا التجميع, the FAW Main Box Left-Lower Centre Shaft Assembly, is one of those two critical shafts. By splitting the torque, the “separating forces” (the forces of the gear teeth trying to push each other apart) are balanced. This dramatically reduces the stress on the transmission housing and the bearings, allowing the gearbox to be lighter, more compact, and significantly more durable.

ال “logic” of this system requires that both the FAW Main Box Left-Lower Centre Shaft Assembly and its “Upper Right” twin are perfectly “timed” so that their helical gear teeth engage the main shaft at the exact same instant. If the timing is off by a single tooth, one shaft will take the entire load, leading to its rapid and catastrophic failure.

Core Component: The ‘Left Countershaft’ (1701271-A2V)

The backbone of the FAW Main Box Left-Lower Centre Shaft Assembly is the ‘Left countershaft’ (1701271-A2V). This is a single, massive, forged component made from high-carbon, case-hardened steel. It is designed to be the primary torque-bearing component in the main box.

Its function is to “counter” the rotation of the input shaft. The input shaft’s gear is in permanent, constant mesh with the “input drive gear” on this FAW Main Box Left-Lower Centre Shaft Assembly. This means that any time the clutch is engaged and the engine is spinning, this countershaft is also spinning.

The shaft itself is precision-machined with multiple “steps,” splines, and bearing journals. The splines are used to mount the various drive gears, while the journals provide a mirror-smooth, ultra-hard surface for the main roller bearings to ride on. A bent or twisted countershaft is a catastrophic failure that requires a full transmission rebuild, making the integrity of this core FAW Main Box Left-Lower Centre Shaft Assembly absolutely critical.

The Main Drive Gears (3rd, 4ذ, 5ذ, Reduction)

ال “logic” of the FAW Main Box Left-Lower Centre Shaft Assembly is embodied in its set of fixed, constant-mesh drive gears. This parts list details the following:

• ‘3rd gear-countershaft’ (1701212-A9K)
• ‘4th gear-countershaft’ (1701213-A9K)
• ‘5th gear-countershaft’ (1701214-A9K)
• ‘Reduction gear-countershaft’ (1701217-A7G)

These are the “drive” التروس. They are fixed (splined or press-fit) to the ‘Left Countershaft’ and are *always* spinning at the same speed as the shaft. They are in permanent, constant mesh with their corresponding “driven” التروس, which spin freely on the main shaft (the “العمود الثاني”).

When the driver selects “3rd gear,” they are actually engaging a clutch (أ “synchronizer”) that locks the *freewheeling 3rd gear* to the main shaft. The power flow is then from the input gear, to the FAW Main Box Left-Lower Centre Shaft Assembly, through this ‘3rd gear-countershaft’, to the main shaft, and out to the wheels. These helically-cut gears are designed for quiet, high-torque operation.

Bearing and Alignment System

The entire FAW Main Box Left-Lower Centre Shaft Assembly is supported at both ends by heavy-duty bearings.

• **Front Bearing (1701225-A2V-C00):** This ‘Cylindrical roller bearing with stop ring’ supports the front of the countershaft. It is a “roller” تحمل, designed for extreme radial loads. ال “stop ring” (a circlip) is critical, as it locks the bearing’s outer race into the front transmission housing, setting the shaft’s position.
• **Rear Bearing (1701215-A2V-C00):** This ‘Cylindrical roller bearing’ supports the rear of the shaft inside the main housing.

These bearings are protected by “baffles,” which are oil slingers. The ‘Baffle-countershaft rear bearing’ (1701233-A9P) is secured by a ‘Hex head bolt’ (CQ1511235S). This disc spins with the FAW Main Box Left-Lower Centre Shaft Assembly and flings oil *away* from the rear bearing seal, preventing leaks and ensuring a long service life.

أخيراً, the ‘Circlip-reduction gear’ (1701229-A7G) and ‘Spacer’ (1701247-A7K) are used to lock the ‘Reduction gear’ in its precise location on the shaft. The ‘Woodruff Key’ (1701226-A7G), ‘Flat Key’ (1701228-A7G), and ‘Spring dowel pin’ (Q5280510) are all used to physically lock the various gears to the shaft, ensuring they cannot spin freely and that 100% of the torque from the FAW Main Box Left-Lower Centre Shaft Assembly is transferred.

FAW Main Box Left-Lower Centre Shaft Assembly Parts List

The following table provides the complete, detailed breakdown of all 14 components identified in the ‘Main Box Left-Lower Centre Shaft Assembly’ diagram for the FAW CA4251P66K24T1A3E5 tractor. هذا FAW Main Box Left-Lower Centre Shaft Assembly is a key to the transmission’s torque capacity.

Technical Specifications and Assembly Context

The specifications for the FAW Main Box Left-Lower Centre Shaft Assembly are defined by its function as the core, torque-handling gear cluster of the transmission. The entire FAW Main Box Left-Lower Centre Shaft Assembly is a precision-balanced and matched set.