Understanding the Parts of a Transmission
Transmission Case
The transmission case is the metal housing that contains and protects all the internal components of the transmission. It's built to withstand high heat and pressure, and it's typically made from aluminum or cast iron. Think of it as the skeleton of the transmission.
Gears
Gears are the heart of the transmission. They determine how much power is transferred to the wheels and how fast the car can go. In a manual transmission, you shift the gears yourself; in an automatic transmission, the system shifts them for you based on speed and load.
Types of gears include:
- Input gear: Connected to the engine
- Counter gear: Transfers power between the input and output shafts
- Output gear: Delivers power to the driveshaft
Gears must be perfectly synchronized for smooth operation. Worn or damaged gears can cause grinding noises or slipping.
Clutch (Manual) / Torque Converter (Automatic)
These components manage the connection between the engine and the transmission.
- Clutch: In a manual transmission, the clutch allows the driver to manually engage or disengage power from the engine to the transmission. It includes a clutch disc, pressure plate, and release bearing.
- Torque Converter: In an automatic transmission, this fluid coupling replaces the clutch and allows the engine to spin somewhat independently of the transmission. It uses transmission fluid to transfer power.
If these parts wear out, you may experience slipping, shuddering, or complete transmission failure.
Planetary Gear Set (Automatic Transmissions)
Automatic transmissions rely on a complex system called a planetary gear set. It includes:
- A sun gear (center)
- Planet gears that rotate around the sun gear
- A ring gear that encloses the system
This setup allows the transmission to provide multiple gear ratios automatically without manually changing gears. It’s the key to smooth shifting in automatics.
Hydraulic System
The hydraulic system uses transmission fluid under pressure to engage and disengage gears. It consists of:
- Pump: Pressurizes the fluid
- Valve body: Directs fluid to various clutches and bands
- Transmission fluid: Lubricates parts, cools the system, and helps transmit power
Low or dirty transmission fluid can lead to overheating and gear slippage, so regular fluid checks and changes are critical.
Bands and Clutches (Automatic)
Bands and clutches inside an automatic transmission control which gears are engaged. These parts are activated by hydraulic pressure.
- Bands wrap around sections of the gear train to hold them in place.
- Clutches lock different gears together.
When these wear out, the transmission might slip, shift harshly, or fail to engage gears at all.
Valve Body (Automatic)
The valve body is the control center of the automatic transmission. It contains a maze of channels and passages that direct transmission fluid to the appropriate clutch or band to shift gears.
Symptoms of a faulty valve body include erratic shifting, harsh engagement, or being stuck in one gear.
Output Shaft
The output shaft connects the transmission to the driveshaft (or CV axles in front-wheel-drive vehicles). This is the final stop before the power reaches the wheels. If damaged, it can cause vibrations, strange noises, or loss of motion.
Synchronizers (Manual Transmission)
In manual transmissions, synchronizers help match the speed of the gear you're shifting into with the speed of the engine, allowing for smooth gear changes. When synchronizers wear out, you'll feel grinding when trying to shift—especially into second or third gear.
Shift Linkage and Sensors
- Shift linkage connects the gear shifter to the transmission. In automatics, this includes the shifter cable and mechanism.
- Sensors (like speed sensors and transmission range sensors) communicate with the vehicle’s computer to manage shifting patterns, especially in modern vehicles.
A broken linkage or faulty sensor can prevent the car from going into gear or cause incorrect shifting.