FAW Rear Axle Reduction Gearbox Logic Assembly: Why These 39 Critical Parts Determine Torque and Traction

Welcome to this critical technical guide on the FAW Rear Axle Reduction Gearbox Logic Assembly (Part No. 2402010QA6T). This is the complete “differential” or “carrier” assembly for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This assembly is the “brain” of the drive axle, responsible for both the final gear reduction and traction management.

The FAW Rear Axle Reduction Gearbox Logic Assembly has two vital functions. First, its “reduction gearbox” (the ring and pinion) provides the final torque multiplication (with an io=2.867 ratio). Second, its “logic assembly” (the differential lock) allows the driver to pneumatically lock the axles, forcing both wheels to spin at the same speed for maximum traction.

This in-depth guide is an essential resource for professional driveline technicians and parts specialists. We will deconstruct the entire FAW Rear Axle Reduction Gearbox Logic Assembly into its 39 serviceable components, including the main housing, the ring/pinion set, the differential lock mechanism, and the critical bearings and shims.

Core Component: The Axle Housing Assembly (2402015-A6T)

The foundation of the FAW Rear Axle Reduction Gearbox Logic Assembly is the ‘Rear axle reduction gearbox housing assembly’ (2402015-A6T). This is the main “carrier” or “pumpkin,” a massive, heavily-ribbed casting made from high-strength ductile iron. This component is the “skeleton” that holds every other part in this list in perfect alignment.

This housing (2402018-A6T) is precision-machined with bores for the main differential bearings (2402049-A6T) and the pinion shaft bearings. These bores are secured by ‘Reducer bearing cap’ (2402024-1H) and ‘Reducer bearing cap’ (2402019-A6T), which are line-bored as a matched set.

The primary logic of this FAW Rear Axle Reduction Gearbox Logic Assembly housing is to maintain the **gear mesh**. The alignment between the ring gear and the pinion gear must be perfect, down to a few thousandths of an inch. Any misalignment will cause a “howl” or “whine” and will quickly destroy the gearset. This housing is the zero-tolerance foundation for the entire FAW Rear Axle Reduction Gearbox Logic Assembly.

The “Reduction” Logic: Ring and Pinion (io=2.867)

The “Reduction Gearbox” part of the FAW Rear Axle Reduction Gearbox Logic Assembly is the main gear set, specified here as ‘Rear axle reduction gearbox assembly (io=2.867)’ (2402010QA6T and 2403010QA6T). This is the “ring and pinion” set.

The “io=2.867” is the critical “logic” – it is the **Input/Output ratio**. This means that for every 2.867 revolutions of the driveshaft (the pinion gear), the ring gear (and thus the wheels) will rotate exactly *once*. This is the final gear reduction in the entire powertrain, multiplying the torque from the transmission to provide the immense power needed to move a fully-loaded trailer.

The ‘Pinion shaft assembly’ (2402065-A6T) is the “input” gear, which is connected to the driveshaft. It is supported by a ‘Tapered roller bearing assembly’ (2402050-A8T-C00) and a ‘Cylindrical roller bearing assembly’ (2402075-A6T-C00). This shaft is sealed by the critical ‘Pinion shaft oil seal assembly’ (2402055-A8T-C00), which prevents oil from leaking out the front of the FAW Rear Axle Reduction Gearbox Logic Assembly.

The “Logic” Assembly: The Differential Lock (2406025-A3C)

The most important “logic” in the FAW Rear Axle Reduction Gearbox Logic Assembly is the **Differential Lock**. A standard differential (which this assembly also contains) is designed to let the outside wheel spin faster than the inside wheel during a turn. However, in low-traction (mud, ice, gravel), this logic is a weakness, as it will send 100% of the power to the one wheel that is spinning uselessly.

The ‘Fork assembly’ (2406025-A3C) and its ‘Fork’ (2406024AA6T) are the heart of the “diff lock” system. When the driver flips the “diff lock” switch in the cab, a pneumatic ‘Air cylinder’ (2406016-A6T) (powered by air from the ‘Air cylinder inlet bolt’ 2406017-A0E) moves a shaft. This shaft moves the ‘Fork assembly’, which in turn slides a ‘Sliding gear’ (2406032AA6T) into place.

This sliding gear physically *locks* the differential’s “spider gears,” forcing both axle shafts to rotate at the *exact same speed*. This bypasses the differential action and ensures that both wheels receive equal torque, providing maximum traction. The ‘Return spring-inter wheel differential lock’ (2406028-A0E) disengages this lock when the air pressure is released. This “on-demand” traction logic is what makes the FAW Rear Axle Reduction Gearbox Logic Assembly so effective.

Precision Shimming: The Adjustment Gaskets

The long-term survival of the FAW Rear Axle Reduction Gearbox Logic Assembly depends on its “shimming.” The parts list details a large number of ‘Adjustment gaskets’ and ‘Adjustment rings’ (2402088D1HB2, 2402091D1H, 2402098-A6T, 2402099-A6T, 2403072-A6T, 2403074-A9T, 2403073-A6T, 2403070-A6T).

These are not standard gaskets; they are **selective shims**. They are used by a technician to set two critical, non-negotiable tolerances:

1. **Bearing Preload:** The precise “squeeze” on the tapered roller bearings (2402049-A6T, 2402050-A8T-C00). Too loose, and the shaft “walks”; too tight, and the bearing seizes.
2. **Gear Backlash:** The tiny “gap” between the ring and pinion gear teeth. Too much gap, and the teeth “hammer” each other, “clunking” and eventually breaking. Too little gap, and the gears bind, whine, and are destroyed by friction.

A technician must use a dial indicator to measure these tolerances and then select the *exact* combination of these “as needed” (按需) shims to build the FAW Rear Axle Reduction Gearbox Logic Assembly to perfect factory specifications. This shimming logic is the most advanced part of servicing the FAW Rear Axle Reduction Gearbox Logic Assembly.

FAW Rear Axle Reduction Gearbox Logic Assembly Parts List (1/2)

The following table provides the first part of the detailed breakdown for the FAW Rear Axle Reduction Gearbox Logic Assembly.

FAW Rear Axle Reduction Gearbox Logic Assembly Parts List (2/2)

This table details the remaining components for the FAW Rear Axle Reduction Gearbox Logic Assembly.

Technical Specifications and Assembly Context

The specifications for the FAW Rear Axle Reduction Gearbox Logic Assembly are defined by its dual function as a final-drive reduction gear and a pneumatically-actuated differential lock. The FAW Rear Axle Reduction Gearbox Logic Assembly is the “logic” of the drive axle.