General information

Manual transmission / General information

Description
1 The manual transmission is mounted transversely in the engine bay, bolted directly to the engine. This layout has the advantage of providing the shortest possible drive path to the front wheels, as well as locating the transmission in the airflow through engine bay, optimising cooling. The unit is cased in aluminium alloy.

2 Drive from the crankshaft is transmitted via the clutch to the transmission input shaft, which is splined to accept the clutch driven plate.

3 All forward gears are fitted with syncromeshes. When a gear is selected, the movement of the cabin floor-mounted gear lever is communicated to the transmission by a selector rod. This in turn actuates a series of selector forks inside the transmission which are slotted onto the synchromesh sleeves.

The sleeves, which are locked to the transmission shafts but can slide axially by means of splined hubs, press baulk rings into contact with the respective gear/pinion. The coned surfaces between the baulk rings and the pinion/gear act as a friction clutch, that progressively matches the speed of the synchromesh sleeve (and hence the transmission shaft) with that of the gear/pinion. The dog teeth on the outside of the baulk ring prevent the synchromesh sleeve ring from meshing with the gear/pinion until their speeds are exactly matched; this allows gear changes to be carried out smoothly and greatly reduces the noise and mechanical wear caused by rapid gear changes.

4 Drive is transmitted to the differential crownwheel, which rotates the differential case and planetary gears, thus driving the sun gears and driveshafts. The rotation of the planetary gears on their shaft allows the inner roadwheel to rotate at a slower speed than the outer roadwheel during cornering.

5 Transmission fluid drain and filler plugs are provided, and a magnetic swarf collector is located in the bottom of the transmission casing.

6 When overhauling the transmission, due consideration should be given to the costs involved, since it is often more economical to obtain a service exchange or good secondhand transmission rather than fit new parts to the existing transmission.

7 This Chapter covers the 084 4-speed and 085 5-speed transmissions.

Manual transmission overhaul - genera/ information
8 The overhaul of a manual transmission is a complex (and often expensive) engineering task for the DIY home mechanic to undertake, which requires access to specialist equipment. It involves the dismantling and reassembly of many small components, the precise measurement of clearances and if necessary, adjustment by the selection shims and spacers. Internal transmission components are also often difficult to obtain and in many instances, extremely expensive.

Because of this, if the transmission develops a fault or becomes noisy, the best course of action is to have the unit overhauled by a specialist repairer or to obtain an exchange, reconditioned unit.

9 Nevertheless, it is not impossible for the more experienced mechanic to overhaul the transmission if the special tools are available and the job is carried out in a deliberate stepby- step manner, to ensure that nothing is overlooked.

10 The tools necessary for an overhaul include internal and external circlip pliers, bearing pullers, a slide hammer, a set of pin punches, a dial test indicator and possibly a hydraulic press. In addition, a large, sturdy workbench and a vice will be required.

11 During dismantling of the transmission, make careful notes of how each component is fitted to make reassembly easier and accurate.

12 Before dismantling the transmission, it will help if you have some idea of where the problem lies. Certain problems can be closely related to specific areas in the transmission which can make component examination and renewal easier. Refer to “Fault finding” at the end of this manual for more information.