Motorcycle Transmission Guide

Key Points

• Motorcycle transmissions are crucial for allowing the engine to operate independently of the wheels when stationary and for keeping the engine RPM within an optimal range for efficiency and power across different speeds.
• Most motorcycles feature manual transmissions operated by a foot lever and a hand clutch, though automatic options like CVT, Honda's DCT and systems used in electric motorcycles are available.
• Key components of a motorcycle transmission include bearings, input/main shaft, output/countershaft, gears (fixed, freewheeling and slider), shift fork, shift drum and shift linkage, which work together to manage engine power and speed.
• Common issues with motorcycle transmissions can include clunking noises, hard shifting, jumping out of gear and difficulty finding neutral, requiring skilled technicians for diagnosis and repair.
• The Motorcycle Technician Training programs at Motorcycle Mechanics Institute (MMI) prepare students for careers in motorcycle maintenance and include training on transmission configurations and troubleshooting.

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.

How Does a Motorcycle Transmission Work?

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 image below:

Automatic motorcycle transmissions

Automatic transmissions exist in motorcycles in a few forms:

• 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.

Manual motorcycle transmissions

While automatic transmissions have made their way to the market, manual motorcycle transmissions are still a staple in the biking world. In fact, most motorcycles feature manual transmissions operated by a foot lever and a hand clutch.

Manual transmissions offer an engaging experience with tactile feedback. Typically, they follow a standardized gear pattern—one down for first gear and the rest up for subsequent gears, with neutral between first and second. This allows riders to smoothly transition through gears.

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.

• 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.

• 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.

• 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.

Motorcycle Gears Explained

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:

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:

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:

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 is common 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 a challenge and 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?

FAQs

What advancements have been made in motorcycle transmission technology?

Advancements in motorcycle transmission technology include semi-automatic gearboxes and dual-clutch transmissions (DCT). These innovations enhance rider experience by offering smoother gear shifts and improved performance without the need for a manual clutch.

How can a rider optimize gear usage for better performance and fuel efficiency?

It’s all about smooth and timely gear shifts, which comes with practice. Maintaining a steady speed, avoiding rapid acceleration and deceleration and using the highest gear possible without straining the engine can improve fuel efficiency.

How many gears does a motorcycle have?

Motorcycles typically have a range of four to six gears, though some models may have as few as three or as many as seven. The number of motorcycle gears can vary based on the type and purpose of the vehicle, such as sport bikes, cruisers or touring bikes.

Do all manual motorcycles have the same gear pattern?

Not all manual motorcycles have the same gear pattern, but most modern motorcycles follow a standard pattern of one down for first gear and the rest up. Neutral is typically between first and second gear. However, some racing motorcycles may use a reversed pattern where the rider clicks down to upshift, allowing for quicker and more efficient gear changes during high-speed maneuvers.

Learn About Motorcycle Transmissions at MMI

In the 48-week Motorcycle Technician Training program at 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.^1.1,7

MMI students can learn complex topics, like motorcycle transmission configurations in program courses. 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, request information to talk with an Admissions Representative!

Campuses That Offer Motorcycle Mechanic Training

• Phoenix, Arizona
• Orlando, Florida