A transmission is a formidable puzzle for most drivers, made up of many intricate connections between a multitude of transmission parts. The complexity of these parts and how they fit together is intimidating, especially when faced with transmission repairs and failing to understand what is happening or why.
While we must trust our transmission mechanics to take care of the details, a little knowledge of the possibly faulty transmission parts can help put you at ease during the transmission repair process.
The first step in having a basic understanding of the transmission parts is understanding the purpose of the transmission as a whole.
Your automatic transmission is responsible for transferring the power of your engine to the driveshaft and wheels so your car can move within its optimal speed range per minute (RPM).
The transmission maintains this optimal range by shifting the transmission as you go faster or slower.
Related Article: What is Gearbox?
What Are the Parts of a Transmission?
A large number of components make up all the parts of an automatic transmission. Still, every automatic transmission has these eight main parts, and they are all integral to the proper workings of your transmission.
But you need to know more than just the part names to know how they get your vehicle moving.
The main transmission parts that need to work together are:
- Transmission Casing
- Planetary Gear Sets
- Hydraulic System
- Torque Converter
- Computer
#1. Torque Converter.
Automatic transmissions don’t have a clutch; instead, they have a torque converter. This replaces the clutch and performs the same function. Your transmission can’t shift gears while it’s still engaged to the engine; otherwise, it would snap gears.
That’s why if you suspect that you might have a bad torque converter, you need to address it immediately.
Your torque converter allows your engine to stay running while disconnecting from the transmission – the equivalent of disconnecting your transmission to shift gears by depressing the clutch on a manual transmission.
The crazy thing about torque converters is that they don’t connect an engine to the transmission with a physical connection of nuts, bolts, or gears. Instead, it’s all through transmission fluid.
While a torque converter’s internal workings can be a bit complicated, it’s much like how you can power a fan by pointing another fan at it. Disconnect the first fan, and you can easily stop the second without hurting yourself.
#2. Oil Pump.
The oil pump inside of an automatic transmission works just like any other oil pump. It delivers transmission fluid from the transmission pan to the valve body, which directs it all the various components throughout the transmission as needed.
It’s not an overly complicated component, but it is an integral part of the system and is one of the few components in a transmission that will occasionally fail.
#3. Planetary Gear Set.
Unlike a manual transmission, which has a set of multiple gears that make up the gear box, an automatic transmission has a one or more (usually more) planetary gear sets.
Planetary gears have three sets of gears. The main gear is the sun gear, and it is in the center of the planetary carrier. The second set is the planetary gears. There are typically three or more of these gears and the mesh between the sun gear and the ring gear.
The ring gear surrounds all of the planetary gears with one ring, connecting the entire system and bringing it together. The system works by locking two of the three gear sets at a time. Since each gear set is a different size, this gives you a multitude of gear ratios by merely locking the other gears in place.
It’s an incredibly efficient system – and allows the transmission to utilize a variety of gear options without the setup that a manual transmission uses.
#4. Clutch Packs.
With a manual transmission, you manually select the gear you want to engage – an automatic transmission is a little more complicated. Instead of a manual shifter to get your output to the desired ratio, your transmission uses a clutch pack.
A clutch pack has multiple plates compressed together – when the valve body sends oil pressure to the clutch pack, it locks a certain number of clutch packs together, giving you your desired output ratio. Different amounts of oil pressure engage different quantities of discs, which gives your hub a different gear ratio.
#5. Output Shaft.
Once your transmission has completed all of its internal magic, it delivers power to the driveshaft, which in turn supplies power to the hubs. But your transmission’s output shaft is what drives the drive shaft.
It’s typically not the most complicated component. On one end, you have a gear that connects to the transmission, and on the other end, you have a splined shaft that connects to the driveshaft via a yoke-type universal joint.
#6. Brake Band.
Brake bands serve one purpose – to temporarily hold planetary gears. They allow the engine RPM to get in line with gear ratio before releasing, which allows for smoother shifting.
Brake bands work much like drum brakes, with a piston squeezing the band around a drum. The harder the piston pushes, the more braking power is applied.
#7. Oil Pan.
Just like your engine has an oil pan on the bottom, so does your transmission. It does exactly what you think it would; it holds the excess transmission fluid (oil) for the oil pump to pull from when needed. It typically has a transmission fluid filter attached, either internally or externally.
It’s one of the most basic components of your transmission, but it’s also one of the components most likely to need repairs. The gasket that sits between the transmission housing and pan will naturally wear over time and will need replacement if any amount of leaking is suspected from the gasket seal.
#8. Valve Body.
Your engine has an ECU, and your automatic transmission has a valve body. This component directs all the pressure from the oil pump to all of your transmission components to get the desired results.
From the torque converter to the clutch packs, nothing gets transmission fluid without the valve body telling it where to go.
In an automatic transmission, it’s controlled by sensors, which work directly with the transmission control module (TCM) to control where all the fluids are sent. It’s a complicated component, but it’s the most important one in your transmission.