Transmission parts knowledge for people researching how transmissions work.
A transmission is an impressive puzzle to most drivers, made up of many intricate connections among a multitude of transmission parts. The complexity of these parts and how they fit together is intimidating, especially if you’re facing transmission repairs and you don’t understand what’s happening or why.
While we need to trust our transmission mechanics to take care of the specifics, knowing a little bit about the transmission parts that might be malfunctioning can help to set your mind at ease during the transmission repair process.
The first step to a basic understanding of transmission parts is to understand the purpose of the transmission as a whole. Your automatic transmission is responsible for transferring the power of your engine to the drive shaft and wheels so that your car can move within its optimal range of revolutions per minute (RPM). The transmission maintains this optimal range by shifting transmission gears as you drive faster or slower.
Manual transmissions use a clutch to connect the engine and transmission. They require the driver to shift the transmission gears, which means actually moving the gears in a somewhat linear, sliding transfer to engage with the coordinating gears needed to maintain the proper RPM ratio. Automatic transmissions keep the transmission gears in one place, in a more circular structure. This is not unlike a small solar system, hence the name Planetary Gear Sets.
Using the combination of an outer ring gear, a central “sun” gear, and two or more smaller “planet” gears, which are all constantly meshed together, the transmission takes over the gear shifting from the driver. Much like the solar system, the sun gear is in the centre and remains stationary and the smaller planet gears engage with it and the ring gear to keep the car moving smoothly.
The ring gear is connected to the input shaft, which brings power from the engine. The planet gears exist within a casing or carrier that is connected to the output shaft which carries power to the drive train and wheels. The planet gears are also connected to a clutch pack. The sun gear is connected to a drum, which is connected to the other half of the clutch pack.
Transmission clutch packs are a series of disks, half with splines on the outside edge, and half with splines on the inside edge. These alternating disks are made to fit together to lock and turn together. They do this using hydraulic functionality.
All of the transmission parts are constantly submersed in transmission fluid. This fluid is manipulated to create pressure, which pushes the transmission clutch pack together at the right time. A complex system of tubes moves the fluid around the transmission and torque converter to create this pressure. The transmission hydraulic system has three main purposes: to help control transmission gear shifting, to lubricate the transmission parts to prevent friction damage, and to keep the transmission cool. The fluid pressure within the transmission must be maintained at all times to prevent damage.
The tubes that transfer the transmission fluid have two major external seals at the front and back. The seal at the front protects the connection with the torque converter and the rear seal contains the fluid where the transmission meets the output shaft. Seals are made of neoprene. Within the transmission exists another type of seal, called a gasket, which connects and protects two stationary transmission parts. Gaskets may be made of any of a variety of materials, such as rubber or silicone. Seals and gaskets can harden over time, which might cause leaks and a drop in transmission fluid pressure, both of which can lead to damage to the transmission.
When driving a manual transmission, the driver must engage the clutch or shift into neutral when the vehicle comes to a stop, such as at a red light, or the engine will stall. The torque converter in an automatic transmission allows the engine to continue running when the vehicle is stopped yet still in gear. Torque is defined as a force that causes rotation. The torque converter uses the pressure of the transmission fluid to control the rotation of its parts. When you are stopped at that red light, one half of the torque converter is turning while the other is stationary. When you accelerate, the fluid pressure forces the other half to spin in conjunction with the first half so that vehicle moves forward.
In most cars today, a computer controls the transmission’s function allowing all vehicle systems to work together for optimum fuel economy and power. As many as 30 sensors read all of the various factors such as vehicle speed, engine temperature, engine speed, etc, that control transmission gear shifting to ensure the optimal shift points are used.
The many transmission parts in your vehicle may remain a puzzle, but understanding some of the basics can help you to have a more informed conversation with your transmission mechanics before leaving it in their capable hands.
As Gene Lewis at the Moncton Mister Transmission says,
For a more in-depth explanation, please visit our Transmission School