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A car transmission is a crucial component in the drivetrain that transfers power from the engine to the wheels.
Transmissions can be either automatic or manual, with manual transmissions requiring the driver to manually change gears. Manual transmissions work by using a clutch pedal and shifter to engage or disengage the engine from the transmission.
There are various types of manual transmissions, including dual-clutch, unsynchronized, synchronized/constant mesh, automated and preselector. Automatic transmissions, on the other hand, use a torque converter to change gears and do not require manual shifting.
If you’ve wondered about how a transmission works, the process varies depending on the type of transmission. Whatever type of transmission it is, the answer to what does a transmission do is it enables 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.
How Does a Manual Transmission Work?
Manual transmissions require the driver to manually change gears using a clutch pedal and a shifter. These types of transmissions consist of a set of gears along a pair of shafts, called the input and output shafts.
How does a manual transmission work? With a manual transmission, the driver must 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 act of “pushing in the clutch” releases the pressure plate, which disengages the clutch from the engine. Every time you make a shift, you have to push in the clutch first.
Types of Transmissions
Dual-clutch
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.
Unsynchronized
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 transmissions use pads to slow down the gears. This eliminates the need for double-clutching action.
Automated
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
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.
Preselector
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
How does an automatic transmission work? 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.
Continuously Variable Transmissions (CVT)
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.
Transmission FAQs
What is a transmission and how does it work?
A car’s transmission helps deliver the power from an engine to the wheels. It changes the gears according to your car’s speed to prevent the engine from getting overloaded. It also keeps fuel consumption lower and keeps a car moving.
What is the difference between a manual transmission and an automatic transmission?
An automatic transmission changes the gears for a driver automatically while a manual transmission allows the driver to decide which gear they want to use.
How does an automatic transmission function in a car?
The gearbox can sense a car’s speed changes by measuring the oil pressure of the vehicle while it moves. Because of this function, it can switch the gears accordingly.
Learn About Transmissions at Universal Technical Institute
Universal Technical Institute (UTI) has a courses on powertrains and transmissions in the Automotive Technology program. Students learn:
- How to disassemble and inspect an electronic automatic transmission
- How to diagnose and service an electronic automatic transmission
- How to perform regular fluid maintenance procedures on an automatic transmission
- How to diagnose and service manual transmission clutch, flywheel and clutch control systems
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.
UTI Campuses That Offer Automotive Technician Training
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1 ) UTI is an educational institution and cannot guarantee employment or salary.
2 ) For program outcome information and other disclosures, visit www.uti.edu/disclosures.
Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.
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