What is a Transmission & How Does it Work?

UTI Profile Image Universal Technical Institute Jul 11, 2020 ·

A car transmission is one of the most important components of a vehicle. It’s what moves the power from the engine to the wheels.

There are a variety of car transmissions. Some are automatic, while manual transmissions in stick-shift cars require the driver to complete extra steps for the vehicle to operate effectively.

If you’ve wondered how does a transmission work, the process varies depending on the type of transmission. Whatever type of transmission it is, the answer to what does a transmission do is to enable the gear ratio between the drive wheels and engine to adjust as the car slows down and speeds up.

When a vehicle is stopped, the transmission disconnects the engine from the drive wheels so that the engine can keep idling when the wheels aren’t in motion. Transmissions also enable quick acceleration from a stop and enable the engine to run more slowly to cut down on wear while the vehicle is driving at consistent speeds.

Manual Transmissions

Manual transmissions have a clutch pedal and a shifter the driver uses to manually change gears. These types of transmissions consist of a set of gears along a pair of shafts, called the input and output shafts.

With a manual transmission, the driver has to select the proper gear and engage or disengage the clutch. The transmission uses a flywheel, pressure plate and clutch to engage and disengage the engine from the transmission.

The flywheel and pressure plate are connected to the engine. The clutch is sandwiched between them and is splined to the transmission input shaft. The term “push in the clutch” means to release the pressure plate, which disengages the clutch from the engine. Every time you make a shift, you have to push in the clutch first.

The following are various types of manual transmissions.


This transmission uses two clutches, which can be wet or dry. One clutch operates the even gears (2, 4 and 6). The other clutch operates the odd gears (1, 3, 5 and reverse). Dual-clutch transmissions were common in older cars and are still found in modern race cars. With today’s dual-clutch automated manual transmissions, sometimes called a double-clutch transmission or a twin-clutch transmission, a computer controls the clutch engagement and shifting, bridging the gap between a manual and automatic transmission.


The first manual transmissions were unsynchronized, or “non-synchro.” They were also called rock crushers because drivers would grind the gears together trying to get them to mesh. Trucks used this type of transmission well into the early 1960s because these transmissions were very strong.

Synchronized/Constant Mesh

Synchronized/constant mesh transmissions keep the cluster gear, drive gear and mainshaft gears constantly moving. These types of transmission use pads to slow down the gears. This eliminates the need for double-clutching action.


An automated transmission, sometimes referred to as an AMT, is a manual transmission with a computer controlling the shifting and clutch. The AMT is used in heavy-duty trucks.


Single-clutch is a manual transmission with the computer controlling the shifting and clutch. Shifting and clutch control can be electric, hydraulic or electrohydraulic. The popularity of single-clutch transmissions started to fade as dual-clutches were able to handle increased torque.


A preselector was a manual transmission with a vacuum or hydraulic shift control that was mostly used in the 1930s through the early 1950s. Some preselectors used bands and planetary gears. Basically, whatever forward gear was selected, the next time the clutch was engaged, it shifted to that gear.

Automatic Transmissions

The main automatic vs. manual transmission difference is that with an automatic transmission, the process that powers a manual transmission happens within the transmission itself. Automatic transmissions typically don’t use clutches. Instead, the automatic transmission relies on a torque converter to change gears.

The first automatic transmission, which was more like a semi-automatic transmission because it still had a clutch, has been around in some form since the early 1900s. The first true automatic transmission used in a production car was the Hydro-Matic, in a 1939 Oldsmobile for the 1940 model year. The inventor was Earl Avery Thompson.

Most large SUVs and trucks have traditional automatic transmissions. Here are some terms commonly associated with automatic transmissions.

  • Direct-shift gearbox: A direct-shift gearbox, also called a DSG, has two clutches that disengage alternately in changing gears. DSGs provide smooth acceleration and fast shifting.
  • Tiptronic: A tiptronic gearbox allows an automatic transmission to be shifted manually, via the shifter and/or the steering wheel controls. The drawback is the computer will override/not allow manual mode if the transmission is outside the set parameters.
  • Hydraulic: Hydraulic is the pressure/fluid inside an automatic transmission.

    What about electric cars? Single-gear systems are used in electric vehicles. The power band of an electric motor enables engineers to use compact single-speed transmissions to transfer power to the drive wheels. This can be integrated with the motor or be a bolt-on.

CVT Transmissions

Continuously variable transmissions, called CVTs, are pulley-based transmissions that are primarily used in small vehicles with small engines. CVTs have been used for years in snow machines, ATVs and side-by-sides, to name a few. They’re also more recently popular in hybrid vehicles.

The basic set-up is a primary small drive and a secondary large driven clutch, with a belt or chain to connect the two. The belt or chain will sit low in the primary drive and sit high in the secondary drive at a stop.

As you accelerate, the primary drive will contract, causing the belt or chain to walk up, while at the same time the secondary will expand, causing the belt or chain to walk down.

Learn About Transmissions at Universal Technical Institute

Universal Technical Institute (UTI) has a whole course on Automotive Powertrains & Transmissions in the automotive mechanic school program. Students learn:

  • How to assemble and disassemble an electronic automatic transmission
  • How to diagnose and service an electronic automatic transmission
  • How fluid flows inside an automatic transmission
  • How to assemble and disassemble a manual transmission

    You don’t need any prior automotive experience to attend UTI. Students graduate prepared for entry-level careers as automotive technicians.1

Get information on automotive technician training online, or call 1-800-834-7308 for information.



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