FAW Sub-Box Output Shaft Assembly: Why These 14 Critical Parts Define Drivetrain Performance

Welcome to this critical technical guide on the FAW Sub-Box Output Shaft Assembly. This is the complete “final drive” assembly within the auxiliary “sub-box” of the manual transmission, designed for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor.

The FAW Sub-Box Output Shaft Assembly is the final link in the chain of torque multiplication. It receives power from the main box and the sub-box countershaft, and its “logic” lies in the 2-speed (High/Low range) synchronizer that is built onto it. This assembly is responsible for delivering the final, selected gear ratio to the truck’s driveshaft.

This in-depth guide is an essential resource for professional transmission technicians and parts specialists. We will deconstruct the entire FAW Sub-Box Output Shaft Assembly into its 14 serviceable components, including the main shaft, the ‘Low gear’ and ‘High gear’ synchronizer hubs, the main bearing, and the final output flange.

Core Component: The Output Shaft (1701541-A7G)

The backbone of the FAW Sub-Box Output Shaft Assembly is the ‘Output shaft-sub box’ (1701541-A7G). This is a single, massive, forged component made from high-strength, case-hardened steel. It is the final output shaft of the entire transmission system.

This shaft is precision-machined with multiple splined sections and bearing journals. Its “nose” or “tip” is supported by a pilot bearing inside the transmission’s main shaft, while its “tail” is supported by the large ‘Dual-row tapered roller bearing’ (350614 X4DR-1).

The splined sections of this shaft are the “logic” hubs. They are designed to hold the “sliding sleeves” of the range synchronizer, which are the components that lock either the “High” or “Low” gear to the shaft. The integrity of these splines is critical, as they must transfer 100% of the vehicle’s final drive torque. Any twist or shear in this component of the FAW Sub-Box Output Shaft Assembly is a catastrophic failure.

The “Range” Logic: High and Low Gear Synchronizers

The core “logic” of the FAW Sub-Box Output Shaft Assembly is the 2-speed range selector. This is a single, large synchronizer assembly that provides two speeds: “Low” (a reduction gear) and “High” (direct drive).

**1. Low Range:** The ‘Low gear-sub box’ (1701542FA0L) is the main “driven” gear for the low range. It is in constant mesh with the counter-shaft. When the driver selects “Low,” the ‘Sliding sleeve-sub box synchronizer’ (1701561FA0L) is moved (by a shift fork) to engage its “dog teeth” with this gear, locking it to the ‘Output shaft’. This routes power through the reduction gearset, providing maximum torque. This gear is held in place by the ‘Limit stop ring-low gear’ (1701543-A7G) and ‘Locating washer-low gear’ (1701544-A7G).

**2. High Range:** The ‘High gear synchronizer assembly’ (1701555FA0L) provides the “High” speed. This is typically a “direct drive” 1:1 ratio. When the driver selects “High,” the *same* ‘Sliding sleeve’ (1701561FA0L) is moved in the opposite direction. It disengages from the low gear and locks directly to the transmission’s main input shaft (which is also the “input” to this sub-box). This action “locks” the main shaft and the output shaft together, causing them to spin at the same speed (1:1 ratio), bypassing the reduction gears entirely.

This entire High/Low clutch is a single unit on the FAW Sub-Box Output Shaft Assembly, comprised of the ‘Sliding sleeve’, the ‘High gear’ hub, and the ‘Low gear’. The ‘Spring-sub box synchronizer [outer]’ (1701558-A7G) units are the “detent” springs that provide the “feel” and holding power for the synchronizer keys. The FAW Sub-Box Output Shaft Assembly‘s function is defined by this clutch.

The Output End: Bearing, Flange, and Speedometer

The rear of the FAW Sub-Box Output Shaft Assembly is where power is delivered to the truck and where speed is measured.

**Main Bearing (350614 X4DR-1):** The ‘Dual-row tapered roller bearing’ is the main output shaft bearing. This is a massive bearing pressed onto the ‘Output shaft’ and seated in the ‘Rear housing assembly’. Its dual-row tapered design is critical, as it is designed to absorb the immense radial loads *and* the extreme axial (thrust) loads of the driveshaft pushing and pulling on the transmission. This is a non-negotiable, heavy-duty component of the FAW Sub-Box Output Shaft Assembly.

**Output Flange (1701616-A7G):** The ‘Output flange’ is the final piece. This heavy, forged-steel flange is splined onto the tail of the ‘Output shaft’. The truck’s main driveshaft (propshaft) is then bolted to this flange. This component must be secured with immense force, which is the job of the ‘Locking nut assembly’ (1701620-A7G). This is a prevailing-torque nut designed to never back off.

**Speedometer (1701571-A9P):** The ‘Rod-speedometer driven gear’ (1701571-A9P) is the “drive” gear for the speedometer. It is pressed onto the ‘Output shaft’. As the shaft spins, this gear (often called a “tone ring”) turns a sensor, providing the “vehicle speed” signal to the ECU and dashboard. The ‘Tachometer gear gasket’ (1701572-A7G) is a shim used to set the correct air gap for this sensor.

Finally, the ‘Dust cover’ (1701617-A7G) is a metal shield that is pressed on behind the flange to protect the main output shaft seal (in the rear housing) from road dirt, water, and debris. This small part is critical to the long-term, leak-free operation of the FAW Sub-Box Output Shaft Assembly.

FAW Sub-Box Output Shaft Assembly Parts List

The following table provides the complete, detailed breakdown of all 14 components identified in the ‘Sub-Box Output Shaft Assembly’ diagram for the FAW CA4251P66K24T1A3E5 tractor. A rebuild of the FAW Sub-Box Output Shaft Assembly requires careful attention to the synchronizer components.

Technical Specifications and Assembly Context

The specifications for the FAW Sub-Box Output Shaft Assembly are defined by its function as the final, range-shifting output of the transmission. The entire FAW Sub-Box Output Shaft Assembly is a precision-balanced set.