Understand your automatic transmission

The modern automatic transmission, (when to flush and when not to flush) is one of 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 until there occurs a problem. It is necessary to understand the concepts behind what goes on inside these technological marvels and what goes into repairing them when they fail.

How does a Transmission work?

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 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.
There are two basic types of automatic transmissions based on whether the vehicle is rear wheel drive or front wheel drive.
1) 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 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.

2) On a front wheel drive car, the transmission is usually combined with the final drive to form what is called a transaxle. The engine on a front wheel drive car is usually mounted sideways in the car with the transaxle tucked under it on the side of the engine facing the rear of the car. Front axles are connected directly to the transaxle and provide power to the front wheels. In this example, power flows from the engine, through the torque converter to a large chain that sends the power through a 180 degree turn to the transmission that is along side the engine. From there, the power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles.



Spotting Problems before they get Worse

Watch for leaks or stains under the car:
If there is a persistent red oil leak that you are sure is coming from your car, you should have your shop check to see if it is coming from your transmission or possibly from your power steering system (some power steering systems also use transmission fluid and leaks can appear on the ground in roughly the same areas as transmission leaks.) If all you see is a few drops on the ground, you may be able to postpone repairs as long as you check your fluid level often (but check with your technician to be sure.) If transmission fluid levels go down below minimum levels serious transmission damage can occur (the same advice goes for power steering leaks as well.)

Check fluid for color and odor:
Most manufacturers require that you check transmission fluid levels when the vehicle is running and on level ground. Pull the transmission dipstick out and check the fluid for color and odor. Transmission fluid is a transparent red oil that looks something like cherry cough syrup. If the fluid is cloudy or muddy, or it has a burned odor, you should have it checked by your technician who will most likely advise you to have a transmission drain and refill or a transmission flush.

Be sensitive to new noises, vibrations, and shift behavior
A modern transmission should shift smoothly and quietly under light acceleration. Heavier acceleration should produce firmer shifts at higher speeds. If shift points are erratic or you hear noises when shifting, you should have it checked out immediately. Whining noises coming from the floorboard are also a cause for concern. If caught early, many problems can be resolved without costly transmission overhauls. Even if you feel that you can't afford repairs at this time, you should at least have it checked. The technician may be able to give you some hints on what to do and not do to prolong the transmission life until you can afford the repair.