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A vehicle's transmission is one of the most crucial components. It is responsible for transmitting power from the engine to the wheels.

Car transmissions come in a range of styles. Some are automated, while manual transmissions in stick-shift cars necessitate additional steps from the driver in order for the vehicle to function properly.

If you've ever wondered how a transmission works, the procedure differs depending on the transmission type. What does a gearbox do, regardless of the type, is to allow the gear ratio between the drive wheels and the engine to vary when the car slows down and accelerates up.

When a vehicle comes to a complete stop, the transmission disconnects the engine from the driving wheels, allowing the engine to idle while the wheels are not moving. Transmissions also allow for swift acceleration from a stop and let the engine to run at a lower RPM to reduce wear while the vehicle is travelling at a constant pace.

Manual Transmissions

A clutch pedal and a shifter are used by the driver to manually change gears in a manual transmission. These transmissions have a series of gears that run along two shafts called the input and output shafts.
The driver of a manual transmission must pick the appropriate gear and engage or release the clutch. The engine is engaged and disengaged from the transmission using a flywheel, pressure plate, and clutch.

The engine is connected to the flywheel and pressure plate. The clutch is splined to the transmission input shaft and sandwiched between them. The expression "push in the clutch" refers to disengaging the clutch from the engine by releasing the pressure plate. Every time you make a shift, you must first engage the clutch.

The numerous varieties of manual transmissions are listed below.

Dual-Clutch


This transmission has two clutches, one of which is wet and the other is dry. The even gears are controlled by a single clutch (2, 4 and 6). The odd gears are controlled by the other clutch (1, 3, 5 and reverse). Dual-clutch transmissions were widespread in older cars and are still used in racing cars today. A computer regulates clutch engagement and shifting in today's dual-clutch automated manual transmissions, also known as double-clutch transmissions or twin-clutch transmissions, bridging the gap between manual and automatic transmissions.

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 transmission 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

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.

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