Manual Transmissions

In the first week we had to disassemble and measure the components of the gear box.

The purpose of a transmission is to produce the torque required to get the vehicles wheels moving along the road. the transmission provides a range of gearing which allows the engine to operate at different speeds  to suit the condition of the terrain the vehicle is on. for example on take off you want a lot of torque to get moving.

Before dismantling we had to do a visual check of the exterior, looking for cracked housings, bolts missing, threaded holes blocked etc. We also had to check that it selects each gear. The gearbox we where given only selected 2nd gear. The cause of the fault could be incorrect re-assembly, we found out that was problem. The end bearing cir clips were not installed properly so the gears were not meshing properly.

There are many types of bearings within the gearbox, they all have different properties to them. Cage roller, Ball race, Tapered roller, Needle bearings just to name a few. We checked all the bearings for pitting and signs of damage. Reverse gear doesn't all ways have a bearing, it has a bush. This is because reverse gear is not a main drive gear and not used as heavily as the forward moving gears.

The gearbox uses a synchromesh system to select gears. The syncromesh system is made up of a hub, sleeve, baulk rings, inserts,and springs. 

The hub is splined to the mainshaft and the sleeve is splined to the hub. The inserts fit between the hub and the sleeve. They lie in slots in the hub and are held outward by a spring at each end. They have a small bead which locates them in a groove in the sleeve. The baulk rings located at each end of the hub have slots for the inserts. they are made of bronze or aluminium and have a coned inner surface to match the steel cones on the gears. the teeth on the outer edge of the baulk rings, the small teeth on the gears, and the splines inside the sleeve are all the same size. How the synchro system works. When the sleeve is moved to select a gear the inserts move and hold the bead of the insert into the slot in the sleeve. the inserts push the cone of the baulk ring against the cone of the gear, friction between these two surfaces slow the shaft or speed the shaft up so that the parts turn at the same speed. once the speed is synchronised the sleeve can slide over the small teeth of the baulk ring and gear. Once the sleeve is engaged with the gear teeth, the gear will be connected to the mainshaft and gear selection complete.

Gear Ratios.
The gear ratio is determined by the number of teeth in each gear. To work out the gear ratio of each gear you can use a formula, ratio=driven gear/driving gear.  gear ratios are used to get the optimum output of the engine   under different circumstances.