The modern automatic transmission is by far the most complicated mechanical component in today’s automobile. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony.
What is a transmission?
The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels. An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range and it is the transmission’s job to make sure that the power is delivered to the wheels while keeping the engine within that range. It does this through various gear combinations. In first gear, the engine turns much faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be going in excess of 70 MPH. In addition to the various forward gears, a transmission also has a neutral position which disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction allowing you to back up. Finally, there is the Park position. In this position, a latch mechanism (not unlike a deadbolt lock on a door) is inserted into a slot in the output shaft to lock the drive wheels and keep them from turning, thereby preventing the vehicle from rolling.
On a rear wheel drive car, the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal position. A drive shaft connects the rear of the transmission to the final drive or rear differential, which is located in the rear axle and is used to send power to the rear wheels. Power flow on this system is simple and straight forward going from the engine, through the torque converter, then through the transmission and drive shaft until it reaches the final drive where it is split and sent to the two rear wheels.
The highly complex functional nature of a transmission brings with it a requirement for regular scheduled replacement of the critically important fluid which is required to lubricate all of the seals and moving parts. Parts that move at intense speed create significant friction and friction builds heat. We warm our hands by rubbing them together. Add a little oil to the palm of your hands before rubbing them together and you will experience the simple effect of lubricating moving parts to reduce friction and heat. The moving parts inside your transmission require proper lubrication so as not to prematurely wear and overheat. Don’t be fooled however into thinking that your transmission gears, clutches and bands aren’t wearing as you drive. Over time, regular use will cause the metal parts to wear normally and we will find microscopic metallic particles suspended in the transmission fluid. When you combine the intense heat that is created and the normally occurring wear the result is burnt and contaminated transmission fluid that is not providing adequate viscosity or lubricating properties. Contaminated fluid smells burnt and looks dark and opaque. Fresh vital transmission fluid has a nice clear vivid, normally dark pink colour. What does your fluid look and smell like? Vehicle manufacturers have established maintenance intervals for transmission fluid change. These intervals are established to ensure that your vehicles transmission functions efficiently and does not experience premature wear or overheating. The maintenance interval will depend greatly on the driving application. Do you drive primarily city or highway? Do you tow a trailer or carry heavy loads? Each driving application brings different maintenance requirements.
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