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What Is a Motorcycle Transmission?

Mar 15, 2021 ·
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There are a number of key components that make up your motorcycle, and each one helps keep it operational on the road. One of the major parts is the transmission. Before getting into what a transmission is and how it works, let’s start with the basics.

In any vehicle (motorcycle or otherwise) a transmission has two main purposes:

  • It allows the engine to spin free of the wheels when the vehicle is at rest.
  • It keeps the engine speed in the correct range relevant to vehicle speed.

Internal combustion engines have a relatively narrow power band. If the engine speed, measured in revolutions per minute (RPM), is either too high or too low, engine power and efficiency will not be optimal. Transmissions contain multiple gear ratios, which keep the engine RPM in an ideal range and allow the vehicle to accelerate from a stop, cruise at high speed, and everything in between.

Motorcycle Transmission Specifics

A motorcycle transmission accomplishes the same two main objectives mentioned above. However, it is packaged in a compact manner so it remains small and lightweight.

Many Harley-Davidson motorcycles use a stand-alone transmission fastened to the engine and driven by an external primary drive. Most other motorcycles use a design where the transmission and engine are one complete unit, as seen in the below image:

Motorcycle transmission graphic

Image credit: Suzuki Motor Corp.

Automatic Motorcycle Transmissions

Most motorcycle transmissions shift manually via a foot-operated lever and a hand-operated clutch. Automatic transmissions exist in motorcycles in a few forms, which we will cover in more detail in a later blog post:

  • Continuously Variable Transmission (CVT) in scooters and mopeds
  • Honda’s Dual Clutch Transmission (DCT) with full automatic mode
  • Electric motorcycles — not exactly automatic, but no manual shifting needed

An automatic motorcycle transmission completes the same tasks as a manual transmission. It allows the vehicle to come to a full stop without stopping the engine and requiring the rider to shift through a range of gear ratios for multiple speeds.

Motorcycle Transmission Parts

Motorcycle transmissions use a series of internal and external parts to maintain an ideal RPM range. These include:

  • Bearings: Pressed into the outer engine or transmission case, bearings allow the transmission shafts to spin free and true.
  • Input/main shaft: Driven by the engine via the clutch pack, the input/main shaft is how the transmission receives power.
  • Output/countershaft: Driven by the main shaft, the output/countershaft delivers power to the final drive via a sprocket or driveshaft.
  • Gears: Motorcycle transmissions have three gear types — fixed, freewheeling and slider. Two constantly meshed gears make up each gear ratio, meaning a six-speed transmission will have 12 gears. See more on the types of gears and related mechanisms below:
    • Fixed gears are part of, or locked to, the main shaft or countershaft and rotate at the same speed.
    • Fixed gears graphic

      Image credit: Suzuki Motor Corp.


    • Freewheeling gears spin independently of the main shaft or countershaft. They have dogs (protrusions) or slots on their sides so they can engage with a neighboring gear.
    • Freewheeling gears

      Image credit: Kawasaki Motors Corp. USA


    • Slider gears spin with the shafts (main or counter); however, they are free to move horizontally on the shaft. As they slide to engage their neighboring freewheeling gear, they make the freewheeling gear temporarily fixed.
    • Slider gear

      Image credit: Suzuki Motor Corp.


    • Shift fork: The shift fork(s) control the horizontal movement of the slider gears.
    • Shift drum: The shift drum controls the movement of the shift forks.
    • Shift linkage: The shift linkage connects the foot-controlled gear selector to the shift drum. As a rider moves the gear selector up or down, the shift linkage rotates the shift drum, causing the shift forks to move slider gears to engage with their neighboring freewheeling gear.

    • In the image below, you can see how the shift forks engage with the sliding gears. As the rider shifts the gear selector, slider gears move back and forth.

      Shift forks engaging with slider gears

How Does a Motorcycle Transmission Work?

Analyzing a power flow diagram is a great way to understand how a motorcycle transmission works. This power flow diagram shows what happens when a motorcycle is in first gear:

Motorcycle first gear graphic

Image credit: Yamaha Motor Corp. USA

  1. Engine power enters the transmission main shaft via the clutch.
  2. Gear M1 is a fixed gear (spins at same speed as the main shaft).
  3. Gear C1 (freewheeling gear) is in constant mesh with M1.
  4. C5 is a slider gear; when it engages C1, the countershaft spins.
  5. Power exits the transmission via the sprocket to the drive chain.

This power flow diagram shows what happens to the transmission when the motorcycle is in fourth gear:

Motorcycle fourth gear graphic

Image credit: Yamaha Motor Corp. USA

  1. Engine power enters the transmission main shaft via the clutch.
  2. Gear M4 is a fixed gear (spins at the same speed as the main shaft).
  3. Gear C4 (freewheeling gear) is in constant mesh with M4.
  4. C2 is a slider gear; when it engages C4, the countershaft spins.
  5. Power exits the transmission via the sprocket to the drive chain.

And this power flow diagram shows what happens to the transmission when the motorcycle is in neutral:

Motorcycle in neutral graphic

Image credit: Yamaha Motor Corp. USA

  1. Power enters the transmission main shaft via the clutch.
  2. All three fixed gears (M1, M4 and C3) mesh with freewheeling gears.
  3. The countershaft does not spin.

Common Problems With Motorcycle Transmissions

While modern motorcycles are reliable and well-built, transmission issues may still occur at some point. It isn’t uncommon for a motorcycle owner to complain about:

  • Clunking noises
  • Hard/difficult shifting
  • Jumping out of gear
  • difficulty finding neutral

A skilled technician can determine the difference between a transmission issue and a clutch issue, as both can present similar concerns for a motorcycle owner.

Gaining access to a motorcycle transmission can be challenge, and it can be a time-consuming process. A motorcycle technician will often eliminate all other possible causes of the complaint before “splitting the cases” to access transmission components.

Read: What Is a Small-Engine Mechanic?

How Does This Knowledge Apply to a Career in the Field?

Transmissions may be the most intimidating driveline component for motorcycle owners. Riders believe transmissions are complex, expensive and hard to access. This translates into job security for a technician who understands transmissions and has the ability to repair them.

Like anything else, experience and practice will allow an entry-level technician to gain confidence in their ability to troubleshoot and repair transmission issues.

Train for the Motorcycle Industry in Less Than a Year

In the 42-week7 Motorcycle Technician training program at Motorcycle Mechanics Institute (MMI), students can learn the foundations of motorcycle, all-terrain vehicle (ATV), side-by-side and personal watercraft maintenance to prepare for an exciting career as a technician.1

MMI students learn a lot in program courses, including transmission configurations. This includes disassembling and troubleshooting transmission issues to become familiar with how they work and what to do if something goes wrong.

To learn more, visit our program page and request information to talk with an admissions representative today.

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