Generally, the car
transmission has gears which shift to help to move faster. If the transmission starts to slip or the car won't move, the transmission requires to be replaced. The transmission is also possible automatically and manually. Automatic transmission shifts by itself and a manual transmission uses a gear shift. Both have to be taken out differently.
The requirement for a transmission in an automobile is a consequence of the characteristics of the internal combustion engine. As usual engines work over a range of 600 to about 6000 revolutions per minute, when the car's wheels rotate between 0 rpm and around 2500 rpm.
The engine provides its highest torque outputs roughly in the middle of its range, while often the greatest torque is required when the vehicle is moving from rest or traveling slowly.
Therefore, a structure that transforms the engine's output so that it can provide high torque at low down speeds, but also run at highway speeds with the motor still operating within its limits, is required.