Manual Gearbox Technical Information

INPUT SHAFT

Connects the clutch to the gearbox.

The end nearest the engine forms a splined shaft which connect in to the clutch friction plate.

The other end has gear teeth that drive the other gears.


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BAULK or SYNCHRO RING

This is at the heart of the gear shift. The ring, usually made of brass locks on to the gear cone. Small external lugs prevent the synchrohub from engaging until the speed of the gear matches the speed of the shaft.


Synchromesh repaired

SYNCHRO HUB

Connects the gear to the Mainshaft.

An outer slider is splined to and inner member that is connected to the mainshaft by a spline.

Small ‘Dog Teeth’ on the gear engage with an internal spline in the outer sliding hub when it is engaged by the selector fork.

Within the Hub the synchro or baulk ring enables smooth and quiet gear changes. The hub applies pressure to the ring that locks on to a tapered cone on the gear. When the speed of the gear is matched to the speed of the output shaft the outer hub is able to engage with the dog teeth

Stop gears crunching

SELECTOR FORK

Each pair of gears has it’s own selector fork.

Engages in a channel in the outer surface of the synchrohub sliding sleeve to engage or disengage gears. Some selector forks have a plastic surface at the ends of the fork.

It is moved back and forwards by the gearbox selector mechanism and is located on a sliding shaft or rail.

A blocker mechanism prevents more than one fork moving at a time.

Gearbox selectors

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crownwheel and pinion

MAIN SHAFT

The output from the transmission. Gears are located on bearing surfaces on the shaft and lock on to synchrohubs to engage drive, which are splined to the shaft.

Rear wheel drive gearboxes are connected to the rear axle by a spline at the rear end of the main shaft while front wheel drive mainshafts have a pinion gear at the end to drive the crownwheel.

CLUTCH

Connects the engine to the gearbox.

Bolted to the engine flywheel is the pressure plate squeezes against the driven plate using a diaphragm spring, the friction plate has surfaces covered in a friction lining.

Either hydraulic pressure or a cable presses the thrust bearing against the pressure plate to release the drive.

clutch repairs taper roller ball bearing thrust bearing

BEARINGS

Bearings are used to locate the gears and shafts.

They have to deal with radial and thrust loading.

Taper roller bearings are very good at dealing with thrust while also locating rotating parts. They are used in most modern transmissions’ also in differentials.

Ball bearings are best for radial thrust

Torrington bearings are suitable for thrust only, they are used to take end thrust on gears to control end float.

Wear eventually makes bearings go noisy, it is worth remembering that it is only the bearings that are holding your gearbox together, when they break up your gearbox will suffer very expensive damage to the gears.


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