312001182 - INTRODUCTION - 6 SPEED GEARBOX

CONSTRUCTION SPECIFICATIONS

The structure of the gearbox consists of:

• a gearbox casing containing and supporting the main and layshafts, the gear engagement forks and rods and the gear selector/engagement device;
• the rear cover which contains the 5^th and 6^th speed gears and the bearing retaining plate for the main and layshafts;
• a casing joining the gearbox to the engine, containing the clutch, the thrust bearing and the control linkage.

1. Thrust bearing2. Main shaft3. Satellite gears4. Planet gears5. Toothed ring gear6. 1^st speed driven gear7. 2^nd speed driven gear8. Gearbox casing9. 3^rd speed driven gear10. 4^th speed driven gear11. Rear bearing retaining plate12 - 5^th speed driven gear13. 6^th speed driven gear14. Layshaft15. Rear cover16. 6^th speed driven gear17. Gearbox bell housing

Main shaft

The main shaft consists of:

• gears for 1^st and 2^nd speeds and reverse formed directly on the shaft;
• gears for 3^rd, 4^th and 5^th speeds fitted on the shaft.

The main shaft is supported by a front roller bearing and a rear ball bearing.1. Reverse gear2. Reverse shaft3. Oil seal4. Main shaft front mounting ball bearing5. Main shaft6. 1^st speed gear (formed on the shaft)7. Reverse gear (formed on the shaft)8. 2^nd speed gear (formed on the shaft)9. 3^rd speed driven gear10. 3^rd speed synchroniser ring11. Presynchronisation block12. 3^rd - 4^th speed synchronizer hub13. 3^rd - 4^th speed synchronizer sleeve14. 4^th speed synchroniser ring15. 4^th speed driven gear16. Main shaft rear mounting ball bearing17. 5^th speed meshing bush18. 5^th speed driven gear19. 5^th speed synchroniser ring20. 5^th speed synchroniser sleeve21. 5^th - 6th speed synchroniser hub22. 6^th speed synchroniser ring23. 6^th speed driven gear24. 6^th speed meshing bush25. Roller bearing26. Nut securing the gears

Layshaft

The layshaft consists of:

• 1^st, 2^nd, 3^rd, 4^th, 5^th and 6^th speed gears fitted on the shaft.

The layshaft mounting consists of:

• a front roller bearing
• a rear ball bearing.

1. Layshaft2. Layshaft front mounting ball bearing3. Needle cage4. 1^st speed driven gear5. 1^st speed synchroniser rings6. Presynchronisation block7. 1^st - 2^nd speed synchronizer hub8. 1^st - 2^nd speed synchronizer sleeve9. 2^nd speed synchroniser rings10. 2^nd speed driven gear11. 3^rd speed driven gear12. Spacer13. 4^th speed driven gear14. Layshaft rear mounting ball bearing15. 5^th speed driven gear16. Spacer17. 6^th speed driven gear18. Ball bearing19. Nut securing the gears

Gears

The gears are the following type:

• helical toothed for the forward gears
• straight toothed for reverse gear.

The teeth for all the gears are HCR (High Contact Ratio).The 2^nd and 5^th speed and final drive gears are superfinished after the thermal treatment to guarantee absolute precision for the teeth, as well as quiet operation.

The gears and drive chain components inside the gearbox are lubricated dynamically, by means of the oil flowing along channels and through ports in the casings, the 3rd/4th speed rod and the main shaft. This allows:

• improved torque transmission and greater efficiency against the effects of wear
• manoeuvrability even at low temperatures thanks to the use of synthetic multigrade oil.

Synchronisers

The synchronisers for the forward speeds are Borg-Warner.The layout for the synchronizers is known as the split type, where the synchronizers for 1^st and 2^nd speeds are fitted on the layshaft, whilst those for 3^rd, 4^th, 5^th and 6^th speeds are on the main shaft.This solution reduces gearbox noise when parked in neutral because 3 of the 6 pairs of gears are not driven.The engagement and synchronization loads are also reduced as a result of the corresponding reduction in the inert rotating masses downstream of the crankshaft.The synchronizer on 1^st and 2^nd speeds, (the gears that are most used by the customer and thus subject to the most stress) is a double cone requiring far less engagement force than for a conventional single cone synchronizer of the same size (- 40%).A new pre-synchronizer system comprising thrust bearing blocks is used on all the gears for smoother, more positive gear shifts: in 1^st and 2^nd speeds the sliding gears are supported by a needle cage. The geometry of the reverse gear teeth has been improved to guarantee excellent manoeuvrability and rapid and precise engagement.

Differential

The differential unit is located in the rear part of the gearbox casing.

It comprises:

• a reduction cylinder pair
• a differential housing in a single piece which incorporates the planet and satellite gears.

The differential is supported by two taper roller bearings.The planet gears have a splined internal profile that mesh with the two joints connected to the two driveshafts that transmit the drive to the wheels.1. Differential gear casing2. Ring gear3. Planet gear4. Planet gear5. Satellite gear6. Satellite gear7. Satellite carrier retaining pin8. Satellite carrier pin9. Ring gear retaining bolt