Sliding Mesh Gearbox | 11 Components and Functions You Should Know.

The sliding mesh gearbox is the oldest gearbox used in the automobile industry. A sliding mesh gearbox, also known as a non-synchromesh gearbox or a crash gearbox, is a type of manual transmission used in vehicles. It’s designed to transmit power from the engine to the wheels by using a system of gears with different ratios. In this article, I will discuss the 13 components and also I will discuss how a sliding mesh gearbox works.

Sliding Mesh Gearbox

While sliding mesh gearboxes are less common in modern passenger vehicles due to their operating complexity, they are still used in some specialized applications where their durability and simplicity are valued.

Sliding mesh gearboxs are simple and rugged, making them suitable for heavy-duty applications like trucks and some older vehicles. However, they require more skill to operate smoothly compared to modern synchronized transmissions, where synchromesh mechanisms automatically match gear speeds during shifts, resulting in smoother and quieter gear changes.

These types of gears needs an experienced driver who can easily change the gears with the speed of the vehicle and the road condition. Now these types of gearboxes are used in many harvester machines and some of the low-quality machines.

Components of Sliding Mesh Gearbox

The sliding mesh gearbox needs some important components to operate and change the gears in extreme conditions. These types of gears need experienced hands to operate. The components are-

1. Input shaft.
2. Clutch.
3. Gears.
4. Synchromesh mechanism.
5. Shift forks.
6. Bearing.
7. Main shaft.
8. output shaft.
9. Housing.
10. Seals and gaskets.
11. Mounting brackets.

Each of these components is important to shift the gears from one end to the other. Each of these components is discussed as follows:

#1. Input Shaft

The input shaft is the shaft that connects and helps to transfer the engine power to the sliding mesh gearbox with the help of the components attached to it. This shaft is crucial to connect the clutch and the gearbox in a single unit.

#2. Clutch

The clutch is the important component that cuts off and connects the engine power with the transmission. Without the clutch, the smooth transmission of gears(torque) can’t be possible. When we need to change the gear in the sliding mesh gearbox the clutch disconnects the power from the engine to the gearbox. This disconnection of power helps to protect the sliding mesh gearbox.

#3. Gears

Gears are a set of threaded metals that connect with each other and the torque transfers to the driving shaft. The gears are the important component to transfer and torque to drive the car. Without these gears, the vehicle can run at a single speed without changing the torque ratio.

#4. Synchromesh mechanism

In manual transmissions, the synchromesh mechanism is crucial for smooth gear shifting. It synchronizes the speed of the selected gear with the input shaft to prevent grinding. The gears are the threaded metals, that are in the disconnects position. The synchromesh mechanism helps to connect these gears in a smooth manner.

#5. Shift Forks

Have you seen anyone change the gears in a car? The driver shifts the gear with the lever in hand. Shift forks are used to move the gears on the main shaft, engaging and disengaging them for gear changes. These shift forks help the drivers change the gears without any extra force because of the torque distribution.

#6. Bearing

Bearings are the main reason to operate something in a smooth condition. Bearings support and reduce friction between rotating components, such as shafts and gears. The gears are mounted on the shaft with the help of the bearing for better running conditions.

#7. Main Shaft

The main shaft is the shaft that connects the driving member of the cars. The main shaft connects the input shaft to the output shaft and carries the gears that provide different gear ratios. In the main shaft, there are also a set of gears mounted to transfer and fluctuate the torque ratio of the vehicle.

#8. Output shaft

The output shaft is the shaft that transfers the torque to the differential or the other driving member. The output shaft is responsible for transmitting power from the gearbox to the vehicle’s wheels.

#9. Housing

Housing is the main room where these components are operated safely and freely. The gearbox components are housed within a protective casing to prevent contamination and ensure proper lubrication.

#10. Seals and Gaskets

The seals and gaskets are used in any system to prevent any leakage. Seals and gaskets are used to prevent oil leakage and maintain the integrity of the gearbox housing.

#11. Mounting Brackets

Each and every part of the vehicle needs to be mounted to the chassis for protection. Mounting brackets secure the gearbox to the vehicle’s chassis or frame.

Function of Sliding mesh gearbox

It is the simplest type of gearbox. The clutch gear is rigidly fixed to the clutch shaft. it remains always connected to the drive gear of the countershaft. Three other gears are also rigidly fixed to the countershaft. They are the second-speed gear, first-speed gear, and reverse-speed gear.

Two gears are mounted on the splined main shaft which can be slid by the shifter yoke when the shift lever is operated. These gears are the second speed gear and first and reverse speed gear. They can be connected to the corresponding gears of the countershaft. A reverse idler gear is mounted on another shaft and always remains connected to the reverse gear of the countershaft.

In the sliding mesh gearbox, there is the three-speed gear combination available. These three gear combinations are –

1. First or low-speed gear.
2. Second speed gear.
3. Third, top or high-speed gear.

Each of these gear combinations is discussed below.

# Gears in Natural

When the engine is running and the clutch is engaged, the clutch shaft gears drive the countershaft gear. The countershaft rotates in the direction of the clutch shaft. Note that in a neutral position, only the clutch shaft gear is connected to the clutch shaft gear. Other gears are free and hence the transmission main shaft is not turning. The vehicle is stationary.

#1. First or Low-Speed Gear

By operating the gear shift lever, the larger gear on the main shaft is moved along the shaft to mesh with the first gear of the countershaft. The main shaft turns in the same direction as the clutch shaft. Since the smaller countershaft gear is engaged with the larger main shaft gear, a gear reduction of approximately 3:1 is obtained. That is, the clutch shaft turns three times for each revolution of the main shaft. further gear reduction in the differential at the rear wheels produces a still higher gear ratio, approximately 12:1, between the engine crankshaft and the wheels.

#2. Second Speed Gear

By operating the gear shift lever, the larger gear of the main shaft is demolished from the first gear of the countershaft and then the smaller gear of the main shaft is meshed with the second gear of the countershaft. The main shaft turns in the same direction as the clutch shaft. A gear reduction of approximately 2:1 is obtained. The differential gear reduction increases this gear ratio to approximately 8:1.

#3. Third, top or high-speed gear

By operating the gear shift lever, the second gear of the main shaft and countershaft are demolished, and the second and top gear of the main shaft are forced axially against the clutch shaft gear. External teeth on the clutch shaft gear mesh with the internal teeth in the second and top gear. The main shaft turns with the clutch shaft and a gear ratio of 1:1 is obtained. The differential reduction produces a gear ratio of about 4:1 between the engine crankshaft and the wheels.

#Reverse Gear

By operating the gear shift lever, the larger gear of the main shaft is meshed with the reverse idler gear. The reverse idler gear is always in mesh with the countershaft reverse gear. Interposing the idler gear between the countershaft reverse gear and the main shaft bigger gear, the main shaft turns in the direction opposite to that of the clutch shaft. This reverses the rotation of the wheels so that the vehicle backs.

Diagram of Sliding Mesh Gearbox

A simplified diagram of this gearbox is displayed below.

Advantages of Sliding Mesh Gearbox

This type of gearbox is very simple and efficient in operation. The advantages are-

1. Sliding mesh gearboxes are known for their robust and simple design.
2. These gearboxes can handle high torque loads effectively, which is especially important in applications where the vehicle needs to carry heavy loads or perform heavy-duty tasks.
3. These generally have less slippage in the transmission of power compared to some other transmission types, resulting in more efficient power transfer.
4. These gearboxes are easier to understand, repair, and maintain, making them ideal for situations where specialized mechanics may not be readily available.
5. Because of their efficient power transfer, these gearboxes tend to generate less heat during operation.
6. These gearboxes can provide a smooth and steady power delivery, which can be advantageous in some situations.

Disadvantages of Sliding Mesh Gearbox

In this gearbox, there is a lack of speed variations that make this gearbox unusable in the current situation. The disadvantages are-

1. One of the most significant drawbacks is the need for manual synchronization of gear speeds when shifting. Drivers must match the engine speed with the new gear ratio, which can result in grinding or damage to the gears if not done correctly. This requires a higher level of skill and experience.
2. Gear changes in sliding mesh gearboxes are often less smooth and can be accompanied by a jolt or noise, making for a less comfortable driving experience compared to synchronized transmissions.
3. This type of gearbox is noisy during gear shifts, which can be distracting and unpleasant for drivers and passengers.
4. These types of gearboxes require more effort and attention from the driver, making them less user-friendly for individuals who are accustomed to automatic or synchronized manual transmissions.
5. Novice drivers may find sliding mesh gearboxes difficult to operate smoothly, leading to a steeper learning curve compared to automatic or synchronized manual transmissions.

Conclusion

The sliding mesh gearbox is old in age and discontinued in current times. But, these are the first gearbox that was introduced to the automobile transmission system. The transmission of gears is hard and noisy making this gearbox unusable for the current time.

---

Frequently Asked Questions(FAQ’S)

What types of vehicles commonly use sliding mesh gearboxes today?

Sliding mesh gearboxes are still found in some heavy-duty trucks, agricultural machinery, industrial equipment, and vintage or classic vehicles where their durability and torque-handling capabilities are valued.

Are sliding mesh gearboxes fuel-efficient?

Sliding mesh gearboxes are generally less fuel-efficient than synchronized transmissions due to the inefficiencies and power interruptions associated with manual synchronization during gear changes.

What is “double-clutching,” and why is it necessary with sliding mesh gearboxes?

Double-clutching is a technique used to shift gears in sliding mesh gearboxes. It involves disengaging the clutch twice during a gear change to synchronize the gear speeds. It’s necessary to prevent grinding and damage to the gears.