FAW Roof Assembly: Le 33 Critical Components That Control Your Gears

Bienvenue dans ce guide technique critique sur le FAW Roof Assembly (Partie no. 1702111BA9P). Ce composant est le “Top Cover” ou “Shifter Tower” assembly for the main gearbox in the FAW Jiefang CA4251P66K24T1A3E5 6×4 tracteur semi-remorque diesel. C'est le complet “logique” system that translates driver input into gear selection.

Le FAW Roof Assembly is the command center for the manual transmission. It is not part of the vehicle’s cabin, but rather the complex, utilisable “top lid” of the transmission housing. It contains all the forks, arbres, and interlocks that physically move the synchronizers inside the gearbox. The precision of this FAW Roof Assembly is what ensures a smooth, faire le ménage, and reliable shift.

This in-depth guide is an essential resource for professional transmission technicians and fleet managers. Nous déconstruirons l'ensemble FAW Roof Assembly dans son 33 composants réparables, including the main ‘Shift arm’ (1702226AA0L), the ‘Shift shaft’ (1702121BA9P), the ‘Neutral switch’ (3774010-367), and all the critical detent springs and seals.

Composant principal: The ‘Top Cover’ Logement (1702111BA9P)

Le coeur du FAW Roof Assembly is the ‘Top cover’ (1702111BA9P). This is the main structural housing, precision-cast from aluminum or iron, that bolts to the top of the main transmission case. Ce composant est le “squelette” for all the other internal control components.

This housing is not just a lid. It is precision-machined with multiple parallel bores that are designed to hold the shift shafts (ou “rails”). The alignment of these bores must be perfect, as they ensure the shift forks are held in the exact correct position over the synchronizer sleeves. Any warping or damage to this main housing will make shifting impossible. This core component is the foundation of the FAW Roof Assembly.

This ‘Top cover’ also serves as the main sealing surface. It is sealed to the transmission case by a large gasket (non répertorié) to prevent gear oil from leaking out. The ‘Dust cover-top cover’ (1702231EA7G) is a critical rubber boot that seals the point where the main shift arm (1702226AA0L) exits the housing, preventing water, poussière, and road grime from entering the transmission and contaminating the oil. L'ensemble FAW Roof Assembly is designed as a sealed unit.

Le “Logique” 1: Shift Linkage (Shafts, Bras, and Forks)

Le “logique” de la FAW Roof Assembly is how it converts the driver’s “H-pattern” shift into the movement of a single, specific shift fork. This begins with the ‘Shift arm’ (1702226AA0L), which is the main lever that the external gear stick connects to. This arm pivots on the ‘Shaft-shift’ (1702121BA9P), a hardened steel shaft.

When the driver moves the stick left or right (selecting a “gate,” Par exemple, 1-2 contre 3-4), this ‘Shift arm’ moves the ‘Shaft-shift’ to line up with a specific ‘Shift fork head/lug’ (1702226BA9P). When the driver pushes the stick forward or back, the arm then pushes or pulls this specific lug.

This ‘Shift fork head/lug’ is attached to a rail, which in turn is attached to the main shift forks (detailed in Assembly 153). This action slides the fork, engaging the gear. The ‘Sliding bushing-top cover’ (1702168BA9P and 1702214BA9P) units are the low-friction bronze bushings that allow the shift shafts to slide smoothly with minimal effort. This mechanical logic is the “muscle” de la FAW Roof Assembly.

Le “Logique” 2: Detent and Interlock System

Le FAW Roof Assembly also contains a critical “détente” système. This is what gives the shifter its positive “cliquez” and prevents the transmission from vibrating out of gear. This system is comprised of springs, plungers, and balls:

• ‘Return spring-high gear’ (1702131B73B)
• ‘Return spring-low gear’ (1702132BA9P)
• 'Printemps’ (1702146-A6H)
• ‘Steel ball’ (Q967105)
• ‘Spring-reverse pin’ (1702147BA9P)
• ‘Plunger’ (1702146-A8L)

Each shift rail (arbre) has small grooves or “detents” machined into it (one for each gear, and one for neutral). A ‘Plunger’ and ‘Spring’ are aligned with each rail. When a gear is selected, the ‘Steel ball’ or ‘Plunger’ is forced by the spring into one of these grooves. Ce “écluses” the rail in place, preventing vibration from “popping it out of gear.” Le “cliquez” the driver feels is this ball dropping into its groove. These springs are a critical part of the FAW Roof Assembly‘s “feel.”

Ce FAW Roof Assembly also contains the interlock system, which is a set of pins (like ‘Parallel cut pin’ 1701656-A2K and ‘Post pin’ 1702242-A9P) that physically block the *other* shift rails from moving once one rail has been selected. This is the safety logic that makes it impossible to select two gears at once.

Electronic Sensor: Neutral Switch (3774010-367)

A key electronic component of the FAW Roof Assembly is the ‘Neutral switch assembly’ (3774010-367). This is a simple but critical sensor. It is a plunger-style switch that is threaded into the ‘Top cover’.

When all the shift rails are in their “neutre” position, a groove aligns under this switch, allowing its plunger to drop, which closes an electrical circuit. This sends a “Neutral” signal to the truck’s main ECU. This signal is essential for:

• **Safety Start:** It is part of a safety interlock that prevents the engine from being started “in gear.”
• **Idle Control:** It tells the ECU that the engine is not under load, allowing it to enter its “idle” map for fuel efficiency.
• **PTO Logic:** It is often used as a prerequisite for engaging a Power Take-Off (Prise de force).

A failure of this single switch on the FAW Roof Assembly can lead to a “no-start” condition that can be very difficult to diagnose.

Scellés, Vents, and Fasteners

Le FAW Roof Assembly must be perfectly sealed from the elements but also able to “breathe.” The ‘Breather plug assembly’ (1702165-A8L) is a one-way “capuchon” that allows internal pressure (which builds as the gear oil heats up) to vent *out*, but prevents water and dust from getting *in*.

The ‘Oil seal assembly’ (1702235-A7G) is a critical radial seal that is installed on the main ‘Shaft-shift’ (1702121BA9P). It prevents the gear oil inside the FAW Roof Assembly from leaking out where the shift shaft enters.

L'ensemble FAW Roof Assembly is held together and mounted with a large number of high-grade fasteners. This includes ‘Hex cap bolts’ (CQ1501040), « Boulons à bride hexagonale’ (Q1840825), ‘Hex screw plugs’ (1702148-A6H, 1702149-A8L), ‘Spring gaskets’ (Q40310), and ‘Elastic retaining rings’ (Q43322, Q43226, Q43034, Q43230) to secure all the pins and shafts.

FAW Roof Assembly (Couvercle supérieur de transmission) Parts List

Le tableau suivant fournit l'intégralité, ventilation détaillée de tous 33 components identified in the ‘Top Cover Assembly’ (referred to as the FAW Roof Assembly) schéma du tracteur FAW CA4251P66K24T1A3E5.

Spécifications techniques et contexte d'assemblage

Les spécifications pour le FAW Roof Assembly are defined by its function as the transmission’s mechanical “logique” board. Ce FAW Roof Assembly (Top Cover) is responsible for all gear selection.