in the Toyota 3k/4k gear boxes we were stripping and rebuilding the reverse gears were straight cut instead of helical cut gears this is because the reverse gear runs off of a neutral third sprocket which fits in between the driven and driver to change the way the output shaft is rotating. if the gears we helical cut it would make it very difficult to mesh 3 gears, whereas straight cut teeth slide straight in.
What type of gears are used for all the forward gears in a manual gear box? Explain?
the type of gears used in a manual gearbox to go forward are all helical style gears this is because more than one tooth is engaged at one time making it quieter than straight cut gears and stronger because of the amount of gear that is meshing with one another, this however causes thrust because of the angle of the teeth meaning thrust bearings are required. On heavy duty equipment like bulldozers etc a herringbone cut gear is used this is because more than one gear is engaged at one time and there is no thrust pressure on the shaft.
What is the purpose of a syncromesh unit? Explain
The purpose of a syncro mesh unit is to make the gear changes smooth. The name gives its job away -
it makes sure that the theeth on the two gears about to be enguaged or meshed together are spinning at roughly the sames speed so that your gears dont clunk as they mesh at different speeds. The way that the two gears are slowed to rotate at the same speed is with the brass baulk ring (a brass ring with a row of teeth and a tapered face). it is brass so that the soft metal will wear out faster than the hard shaft, it is also cheeper to replace. it is tapered because two tapers grip extremely thourghly but can also split easily.
How do you check a baulk ring for serviceability?
to check a baulk ring you need to see how close the ring is to the gear if it is able to touch the gear, the taper on the baulk ring has worn down too much, there needs to be a gap. (measured with a feeler guage) The gap would suggest that the tapers are tight against eachother and would do their job.
what is the pupose of a baulk ring?
the purpose of a baulk ring is to mach the speed of the two gears about to be engaged, it does this by having a tapered face which maches the taper on the gear causing the two to spin at the same speed when the two tapered faces are pressed. this system is important because it means that the gears when selected and changed are not under as much load because the speeds of the two rings are spining at almost the same speed.
What type of bearings are used in a gear box?
tapered roller bearings and thrust bearings, both of these bearings are to minimise any side to side/end to end movement.
Give an explanation of a gear ratio.
the way that gear ratios work is from low ratio (torque) to high ratio (power), the input shaft, 1st gear is the smallest gear, 4th gear is usually 1:1 or close meaning the same size gear on the input and output shafts whereas 5th gear on the input shaft is bigger than the corresponding output gear (also known as an overdrive gear).
