FAW Central Bridge Differential Assembly: A Critical Analysis of 12 Core Components

Welcome to this critical technical analysis of the FAW Central Bridge Differential Assembly (Part No. 2503010QA6T). This is the “logic” core of the “centre” or “forward” drive axle for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This is the component that allows the truck to make turns without wheel hop.

The FAW Central Bridge Differential Assembly, also known as the “inter-wheel differential carrier,” is a complex set of gears. It is responsible for receiving power from the driveshaft via the main “ring gear” and then splitting that power between the two “half-shafts” (axles) that go to the wheels.

This in-depth guide is an essential resource for professional driveline technicians and parts specialists. We will deconstruct the entire FAW Central Bridge Differential Assembly into its 12 serviceable components, including the main ‘Differential case assembly’, the ‘Ring gear’, the internal ‘Planetary’ and ‘Half-shaft’ gears, and the critical tapered roller bearings.

Core Component: The Differential Case (2403015FA6T)

The heart of the FAW Central Bridge Differential Assembly is the ‘Rear axle differential case assembly’ (2403015FA6T). (Note: “Rear axle” is used as a generic term for the diff case, but this assembly is for the *centre* bridge). This is the heavy-duty cast iron “cage” or “carrier” that houses the entire internal gearset.

This component is machined with extreme precision, as it must hold the “spider” and “side” gears in a perfect mesh. As shown in the parts list, this case is a two-piece assembly, bolted together to form a sphere:

• ‘Rear axle differential right case’ (2403018FA6T) – 1 unit
• ‘Rear axle differential left case’ (2403017FA6T) – 1 unit

These two halves are machined as a **matched set** and must never be interchanged with halves from another FAW Central Bridge Differential Assembly. The ‘Centre axle driven bevel gear’ (the ring gear) is bolted to the large flange of this case. When the driveshaft spins the ring gear, it is *this case* that rotates, which in turn carries the internal spider gears with it.

The “Reduction” Logic: Ring Gear (2502037EA6T) and Ratio (io=2.867)

The ‘Centre axle reduction gearbox assembly (io=2.867)’ (2503010QA6T) and the ‘Centre axle driven bevel gear’ (2502037EA6T) define the axle’s “reduction” logic. The “io=2.867” is the critical “logic” – it is the **Input/Output ratio**.

This ratio means that for every 2.867 revolutions of the truck’s driveshaft (spinning the pinion gear), this ‘Centre axle driven bevel gear’ (the ring gear) will rotate exactly *once*. This is the final gear reduction in the entire powertrain. It multiplies the torque from the transmission, providing the immense force needed to move a fully-loaded trailer. This is a core function of the FAW Central Bridge Differential Assembly.

The ‘Centre axle driven bevel gear’ (ring gear) is bolted to the ‘Rear axle differential case assembly’ using the 16 ‘Hex flange bolts’ (Q1851845TF2KS). These are critical, high-shear, single-use fasteners that must be torqued in a precise star pattern to prevent the ring gear from warping or shearing off under load. This gear is the primary input to the FAW Central Bridge Differential Assembly.

The “Differential” Logic: Spider and Side Gears

The “logic” of the FAW Central Bridge Differential Assembly is its ability to allow the left and right wheels to turn at different speeds. This is achieved by the internal gearset:

• **’Planetary gear’ (2403056D1H) – 4 units:** These are the “spider gears.”
• **’Half-shaft gear’ (2403051D1HB1) – 2 units:** These are the “side gears.”

Here is how this FAW Central Bridge Differential Assembly works: The four ‘Planetary gears’ are mounted on two shafts (the ‘Long’ 2403061-A6T and ‘Short’ 2403062-A6T) that are fixed *inside* the differential case. The two ‘Half-shaft gears’ are splined to the axle shafts (half-shafts) and mesh directly with these four spider gears.

**When driving straight:** The entire case, spider gears, and side gears all spin as one solid unit. The spider gears do not rotate on their shafts; they simply act as a “solid block,” forcing both side gears (and thus both wheels) to turn at the same speed.

**When turning a corner:** The inner wheel must slow down, and the outer wheel must speed up. The differential “logic” allows this. The inner wheel’s side gear slows down. This forces the spider gears to “orbit” or “walk” around the slower side gear. This “walking” motion, in turn, *accelerates* the other side gear, allowing the outer wheel to spin faster. This action is the core logic of the FAW Central Bridge Differential Assembly.

Thrust Washers and Bearings: The Unsung Heroes

The internal gears of the FAW Central Bridge Differential Assembly are under immense separating forces. The parts list includes ‘Gasket-half-shaft gear’ (2403053D1H) and ‘Planetary gear gasket’ (2403058-A9T). These “gaskets” are actually critical **thrust washers**.

These are hardened, anti-friction washers placed *behind* the side gears and spider gears. They prevent the steel gears from grinding themselves into the soft cast iron of the differential case. A worn-out thrust washer will create excessive “backlash” or “slop” in the differential, leading to a “clunk” on acceleration and eventual gear failure.

The entire FAW Central Bridge Differential Assembly (the case with the ring gear bolted to it) spins within the main axle housing on two massive ‘Tapered roller bearing assembly’ units (2403060-A8T-C00 and 2403070-A6T-C00). These are the main “carrier bearings.” They support the entire weight of the differential, the torque from the driveshaft, and the entire weight of the truck. A failure of these bearings is a critical fault, often heard as a “whine” or “growl.” These bearings are a key serviceable part of the FAW Central Bridge Differential Assembly.

FAW Central Bridge Differential Assembly Parts List

The following table provides the complete, detailed breakdown of all 12 components identified in the ‘Central Bridge Differential Assembly (io=2.867)’ diagram for the FAW CA4251P66K24T1A3E5 tractor. This FAW Central Bridge Differential Assembly is a precision-matched set.

Technical Specifications and Assembly Context

The specifications for the FAW Central Bridge Differential Assembly are defined by its function as a high-torque, final-drive reduction gearset with an integrated differential. The FAW Central Bridge Differential Assembly is the “logic” core of the centre axle.