A Complete Guide of Transmission Shafts

Table of Contents

I. Introduction

Transmission shafts are vital elements in several mechanical transmissions and especially in vehicles. They are primarily the axle that holds the gears on your vehicle in place and transmits power through the gearbox. 

This guide will explain transmission shafts, the functions and different categories of transmission shafts, the materials used to manufacture transmission shafts, design considerations for transmission shafts and the various customizations available for transmission shafts.

II. What is a Transmission Shaft?

Transmission Shafts

A transmission shaft can be explained as a shaft that spins, transferring movement from the engine to the differential gear. The transmission shaft can be manual or automatic whereby the manual transmission operates with several gears to the drive shaft, whereas an automatic transmission uses the planetary gear set to generate various gear ratios.

  • Basic anatomy of a transmission shaft

The transmission shaft consists of several parts. 

Main Case: The main case or casing can be constructed from steel, plastic or aluminum. 

Bearings: Bearings provide support and rotation by rotating under load. 

Bearing Housing – A bearing housing is essential in supporting and protecting a bearing from damage. 

Caps: Caps keep dirt, water and other elements out of the gears. 

Covers: Covers shield both differential housing and gears against dirt and moisture penetration. 

III. Types of Transmission Shafts

  • Main shaft: The main shaft which is also defined as the primary shaft of the gearbox. It is the output shaft and it receives its power from the engine conveying it to other parts. It stretches from the engine block to the back of the transmission.
  • Countershaft: The countershaft passes the motion from the main shaft to the required place. It runs alongside the gearbox’s main shaft and has pinion wheels.
  • Idler shaft: The idler shaft refers to a shaft conveying a gearwheel or more than one gearwheel between the driver and the driven shaft. Its role is to switch direction and allow the change in the direction of rotation by the output shaft for the reverse gear. It also helps give various positioning of gear wheels.
  • Comparison of different types of transmission shafts

All of the transmission shafts mentioned above have different functions and roles when it comes to their applications. Below is the comparison of the functions of each type of transmission shaft:

Main Shaft – This shaft transmits power from the engine to the gearbox.

Transmission Shaft – A transmission shaft is part of a vehicle’s drivetrain (the collection of gears and components connected to an axle). It transmits power from an engine to another component such as a driveshaft or differential.

Idler Shaft – An idler shaft acts as a support for rotating elements in transmissions, such as gears, pulleys and sprockets.

Transmission Shafts

IV. Materials Used for Transmission Shafts

A gear and shaft have toothlike structures, so each tooth can attach to the other, making power pass through. To create different speeds and forces, shafts and gears of varying measurements are used in matching order. Mild steel is used to manufacture shafts, whereas alloy steel, like nickel, is preferred for shafts with more strength. Hot rolling forms the shafts, and cold drawing is used to finish, turn, and grind.

Materials used in the making of shafts should have specific characteristics for efficiency. The machine should bear the characteristic of being effortlessly machined and should contain high strength. It must also be of low sensitivity and ductile and categories of 40 C 8, 45 C 8, 50 C 4, and 50 C 12 of carbon steel should be the ones to be used. The strength and resistance are the core factors to consider when making the shafts.

V. Manufacturing Process of Transmission Shafts

Transmission shafts are usually manufactured using the process of mold designing, rapid prototyping, and CNC machining. Molding is a manufacturing process that molds liquid or other ductile materials through a fixed frame. The mold is normally a space, often metallic, where the liquid plastic or metal or ceramic flows through. The mold is constructed according to the desired end product’s shape.

CNC turning is a type of CNC machining that is the most commonly used procedure in manufacturing shafts. This process involves attaching portions of materials of high-grade steel to chucks and spinning them. While spinning, the materials are cut and shaped into the desired end product by different tools, each at a time. Holes are also drilled through the center of the materials to desired measurements, and later a mill drills holes to give room for lubricant to pass through during its operation. The next step is whereby the inner teeth are shaped using a gear shaper machine and differ from one gear to another. Later, the external teeth are cut, and the gear is inspected to ensure it is aligned well and passed through the heat to strengthen the steel. Carbon is inserted, and the shaft sucks it in, making the steel even stronger, and then it is cooled and hardened. Carburizing is the next step which involves heat to make the part with low carbon steel harder and later soaking, which helps to harden the metal more. Rapid prototyping is crucial at the beginning of the manufacturing process to remember the image of the desired end product and ensure it is identical to the outcome.

VI. Design Considerations for Transmission Shafts

Certain factors need to be checked in a shaft design for its efficiency. They include;

  •   Static stress, whereby a shaft must resist stress from applying torque.
  •   Twist, since too much twisting, can result in problems with timing
  •   Fatigue, because there can be recurring stresses hence making fatigue a crucial factor to be considered
  •   Critical speed should also be known to not work around it.
  •   Slope at the bearings must be maintained within the stated limits to avoid early wearing out.
Transmission Shafts

VII. Maintenance and Replacement of Transmission Shafts

Sticking to a gearbox’s intended role is important to avoid wearing out and malfunctioning. Also, ensuring no oil leaks at the shafts in a gearbox is crucial. Leaking could result in the absence of lubrication.

It is important to ensure that the working environment of the gearbox is clean to avoid contamination which alters the required operating temperature.

Lubricating often is also a factor to keep in mind to ensure the right functioning of the gearbox.

VIII. Customization of Transmission Shafts

Customized transmission shafts are available and carry more benefits than buying a brand-new one. To start with, their performance is of higher capacity and smooth operation, making a vehicle move and a new one since the transmission is built in a way that suits the automobile. Also, customizing is more financially friendly in the long run since one does not keep on losing money to technicians to deal with various issues with the transmission. It also helps to eliminate worries since the transmission is usually built to work efficiently like a new one, and all issues are dealt with. Lastly, it helps increase the life of a vehicle.

DEK is considered the leading manufacturer of shafts from China and has the desired experience in manufacturing shafts. For example, in the case of a worm shaft manufacturer, DEK is aware of its usefulness and provides the best standard worm shaft for efficiency in tuning mechanisms. Also, the bearing shafts from DEK are well recognized for their capacity to decrease energy consumption, the same case as DEK’s motor shaft, which is of very high quality and hollow shaft, which ensures its durability and top-notch strength.

IX. Conclusion

In conclusion, transmission shafts play a very critical role in automotive, and each element plays an important role in the effectiveness of the whole machine.

This guide has described the functions and anatomy of transmission shafts, different categories such as main, countershaft and idler shaft, materials used to manufacture them and their manufacturing process. It emphasizes the significance of designing transmission shafts with effortless machinability, high strength and low sensitivity/flexibility. Furthermore, considerations like static stress, twist fatigue and critical speed must also be considered to guarantee maximum efficiency from each transmission shaft.

Understanding transmission shaft types, materials used in their manufacture, and design considerations are essential to guarantee their efficacy and durability. With technological advances in shaft manufacturing, transmission shafts continue to be customized and improved for different applications and industries – underscoring their significance in mechanical engineering.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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