Manual Transmisson

   What is a manual transmission? There is a shift level, a gear box with 3 selector folks, an Interlock mechanism, 5 different gear ratio, engine provide a constant amount of horsepower with a range of speed 0-7000,8000 etc... rpm, and a manual clutch system.
   now let say the engine is running @ 4000 rpm, 1st gear selected, clock says 33 kph; 2nd says 57 kph; 3rd say 77kph, but then acceleration @ 1st from 0-33 kph is just 2 secs; while @ 2nd 0-57 kph in 5-6 secs, and 3rd gear takes like 9-10 secs just to get up to 4000 rpm.( fictional theoretically relevant in game figures)
  What does that tells you when the formula relating Torque/ RPM/ HP say: "HP = Torque x RPM ÷5252"    (source: http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm). So basically the engine can only provide a limited maximum HP; then Torque and RPM is directly disproportional to each other. Gears allow the driver to select the right torque and speed ratio desired for suitably adapt different speed and load condition. Why in first gear @ same rpm the top speed is low but acceleration is quick, because @ 1st a high gear reduction ratio(3.7:1) between the driven and the driver multiplies the torque transfer up to for example 3.7 times, while it takes the driver 3.7 revs just to make 1 rev output. As we change into higher gear, our speed desire must be over the load desire, therefore a 3.33:1 multiply speed while reducing torque: its only take the driver 3.33 turns to make 1 rev output.
Notable gear: 1st; 2nd; 3rd: gear reduction. In these gear, speed ratio is reduced compare to direct output speed, crowning torque multiplications. Drive is transferred from input, to driver, then driven gear to output to final drive.
                      4th: direct drive ratio, drive from input straigh through output.
                      5th: Overdrive ratio actually for speed multiplication n the reduction of torque, therefore its ratio is 0.86:1=> driver drive less than 1 turn to complete 1 output=> speed improved.

How is drive transferred? What exactly happen?
The magic of the manual is the gear synchronizer assemply, 4 example between 1st n 2nd driven; 3rd n 4th driver, or 5th gear; there are synchro hubs that consist of a cone gear, baulk ring and the sliding hub, what it does is allowing the next gear to be selected smoothly by synchronizing gear teeth to alignment in order to engage the selected gear ratio with the output shaft.
When the next geat is selected, from the driver's shift knob to the shift folk that exert a force on the sliding hub. This pushes the baulk ring to engage in friction against the cone gear(the selected gear) , these 2 start the movement until both's dog teeth are aligned and matched with the grooves inside the sliding hub, then the gear is locked with the engaged shaft.
Reverse is a lil bit special it needs an additional gear to counter the drive direction, this gear is an idler, because of this, it is cost effective n quite reliable to use spur gears cuz they are simple and cheap. 

When selecting gears, it is possible that 2 gears r selected @ the same time, this is no good, an interlock mechanism with its detent ball is used for this reason. it restricts to only 1 gear to be selected at a time, becasue there are 3 shift shafts, and when a gear selected the detent ball n spring locks the shaft 1 place, also pushes the other balls into locking grooves on other shaft, locking them from moving.