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Common Parts of an Automatic Transmission

A large number of components make up all the parts of an automatic transmission.

Every automatic transmission has these eight main parts, all of which are essential for the proper functioning of your transmission.

But to know how they get the vehicle moving, you need to learn more than just the part names.

1. Torque Converter

There is no clutch on automatic transmissions; they have a torque converter instead.

This replaces the clutch and the same function is performed.

Your transmission can’t shift gears while it’s still engaged to the engine; otherwise, it would snap gears.


TORQUE CONVERTER: FUNCTIONS, PARTS, WORKING PRINCIPLES, AND TYPES

TORQUE CONVERTER: FUNCTIONS, PARTS, WORKING PRINCIPLES, AND TYPES
TORQUE CONVERTER: FUNCTIONS, PARTS, WORKING PRINCIPLES, AND TYPES

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.

Depressing the clutch on a manual transmission is the equivalent of disconnecting the transmission to shift gears.

The interesting about torque converters is that they don’t connect an engine to the transmission with a physical connection of bolts, nuts, or gears.

Instead, it’s all through transmission fluid.


Read: 5 CAUSES OF TRANSMISSION FLUID LEAKS AND REPAIR COST

5 Causes of Transmission Fluid Leaks and Repair Cost
5 Causes of Transmission Fluid Leaks and Repair Cost

While the internal workings of a torque converter can be complicated, but, it’s much like how you can power a fan by pointing another fan at it.

Once you’ve disconnected the first fan, you can quickly turn off the second without hurting yourself.

2. Oil Pump

An automatic transmission’s oil pump functions similarly to any other oil pump.

It delivers the transmission fluid to the valve body from the transmission pan, which directs all the various components throughout the transmission as needed.


Read: THE MUST-KNOW OIL PUMP FAILURE SYMPTOMS


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 gearbox, an automatic transmission has 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 centre of the planetary carrier.


Read: MAIN GEAR CONSTRUCTION

Main Gear Construction
Main Gear Construction

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.


Read: WHAT ARE THE MAIN COMPONENTS OF THE GEAR BOX?

What are the Main Components of the Gearbox?
What are the Main Components of the Gearbox?

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.


Read:

GEAR RATIO AND TIRE SIZE CHART

WHAT’S THE DIFFERENCE BETWEEN BRAKE SHOES AND BRAKE PADS?

HOW A CAR CLUTCH WORKS


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.


WHAT IS DRIVESHAFT? WORKING OF DRIVESHAFT

WHAT IS DRIVESHAFT? WORKING OF DRIVESHAFT
WHAT IS DRIVESHAFT? WORKING OF DRIVESHAFT

6. Brake Band

Brake bands serve one purpose – to temporarily hold planetary gears. 

They allow the engine RPM to get in line with the 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.


DIFFERENCE BETWEEN DRUM BRAKE AND DISC BRAKE
DIFFERENCE BETWEEN DRUM BRAKE AND DISC BRAKE

DIFFERENCE BETWEEN DRUM BRAKE AND DISC BRAKE

CONVERT DRUM BRAKES TO DISC BRAKES IN 3 STEPS!

RENEWING DRUM-BRAKE SHOES

WHAT’S THE DIFFERENCE BETWEEN BRAKE SHOES AND BRAKE PADS?


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.


Read: HOW DOES AN OIL SUMP WORK IN YOUR CAR?


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 gaskets around the oil pan often leak transmission fluid and need to be replaced.


Symptoms Of A Blown Head Gasket? How To Prevent And Fix It
Symptoms Of A Blown Head Gasket? How To Prevent And Fix It

HOW TO CHOOSE THE RIGHT GASKETS

DETECTING HEAD GASKET ISSUES AND THE SOLUTION

WHAT ARE THE INTAKE MANIFOLD GASKET LEAK SYMPTOMS?


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.


ECU CHIP TUNE | IGNITION TIMING | INCREASE HORSEPOWER

VALVE MECHANISM CONSTRUCTION

Valve Mechanism Construction
Valve Mechanism Construction

Download: VALVE SELECTION HANDBOOK | PDF


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.

See More:

Ekster EU

8 Comments

  1. Kimetto Nathan February 6, 2020 Reply

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