How a manual gearbox works
Fig. 6.4. Five-speed manual gearbox in section: 1 – dual mass flywheel; 2 – driven disk; 3 – clutch pressure plate; 4 – clutch release bearing; 5 – Front cover of the manual gearbox; 6 – manual gearbox housing; 7 – rear cover of the manual gearbox; 8 – output shaft flange; 9 – secondary shaft; 10 – primary shaft
The torque from the engine is transmitted via the driven disk 2 (Fig. 6.4) to the primary shaft 10 of the gearbox. The forward gear pinions and the reverse gear pinion are located on it. These pinions are engaged with the pinions located on the secondary shaft 9. The reverse gear pinion engages via the intermediate pinion, which changes the direction of rotation to the opposite.
Gears and shafts
If the gear is not engaged at all, the gears of the primary shaft rotate without transmitting torque. When a gear is engaged, one of the gears of the primary shaft connects with the gear of the secondary shaft, and the torque with the corresponding gear ratio is transmitted to the secondary shaft of the gearbox. The ratio of the number of teeth of a pair of gears forms the gear ratio. All gears are synchronized. Thanks to the synchronizers, the speeds of the shaft and the gear located on this shaft are equalized, after which the synchronizer clutch connects with the gear without impact. As a result, the gears are engaged easily and silently. Rubbing elements, braking faster rotating parts, ensure the alignment of the parts coming into contact. Synchronization occurs within fractions of a second, so when changing gears, it is important to move the lever smoothly, with some delay.
Re-throttle is usually not required when operating a fully synchronized gearbox. Only at low temperatures and with thick transmission oil can it help when downshifting.
Forward and reverse gears
Fig. 6.5. Location of gear shift rods in a five-speed manual transmission
The first three forward gears increase torque. The 4th, so-called direct gear, transmits torque in a ratio of approximately 1:1. In 5th gear, the frequency of revolutions of the driven shaft is higher than the frequency of revolutions of the engine. In order for the car to move in reverse, there is an additional gear that changes the direction of rotation of the wheels to the opposite. When you select the desired gear with the shift lever, the movement of the lever through the rods (Fig. 6.5) is transmitted to the shift mechanism in the gearbox.
Sequence of works
1. Move the gear shift lever to neutral position.
2. Place the vehicle on stands and remove the lower engine guard.
Fig. 6.6. Fixing the intermediate levers of a manual gearbox using a drill (arrow) with a diameter of 5.9 mm
3. Fix the intermediate levers (under the shift lever support), inserting a 5.9 mm diameter drill into the holes of the shift mechanism support and intermediate levers (Fig. 6.6). At service stations, a special 5.9 mm diameter locking pin is used for this purpose.
Fig. 6.7. To adjust the rods, loosen the bolts shown by the arrows and move the rods to the set position
4. If the length of each rod is as required, the rods should fit into the intermediate levers of the shift mechanism without additional offset. Otherwise, loosen the bolts (fig. 6.7, arrows) mount the rods to the gearbox and move the rods to the installed position.
5. Move the gearshift lever to neutral position and tighten the bolts in this position.
6. Remove the drill and check the gear shifting with the engine running.