What Is Constant Mesh Gearbox

Constant Mesh Gearbox

Here is the complete guide about Constant Mesh Gearbox. Here we provide Constant Mesh Gearbox working Main Parts, Advantages and Disadvantages etc.

As the name indicates that all the gears on the layshaft and main shaft are in constant mesh with each other and the dog clutch decides the transmission of the required gear to be engaged. For the smooth engagement of dog clutches, it is required that the speed of main shaft gears and the dog clutch must be equal.

Therefore to obtain lower gear, the speed of the layshaft, clutch shaft, and the main shaft must be increased. The shifting of gears was not at all an easy task and only a skilled driver can drive such a vehicle and the special technique required was Double-declutching.

Constant Mesh Gearbox

For a smooth operation of the engine, the constant mesh gearbox is used. They are used to increase the torque, followed by a speed reduction. The transmission is a kind of manual. The first manual machinery system was invented in the nineteenth century. Different gear ratios have different torque and speed ratios. This is also followed by the reverse process. This newly developed manual transmissions contain all the gear mesh at any time.

It can be described technically as a gearbox in which all gears are always meshed. In the original positions, the gears remain fixed. The gears are constantly engaged. Read more in this article about construction, operating, advantages, drawbacks and applications.

Main Parts of Constant Mesh Gearbox


There are 3 shafts present in this gerabox which are :

  • Main Shaft: It is also known as output shaft. It is the splined shaft over which the dog clutches along with gears are mounted. Gears on this shaft are free to rotate.
  • Lay Shaft or Counter Shaft: It is an intermediate shaft between the Main Shaft and Clutch Shaft. The gears of counter shaft are in constant mesh with gears of main shaft. Also the gears of counter are shaft are not free to rotate as they are directly connected to the Counter Shaft.
  • Clutch Shaft: The clutch shaft carries the engine output to the gearbox but act as input for the gearbox. It is also known as input shaft.

Dog clutch

Dog embroidery is a special feature of a continuous mesh transmission. It is used to connect two shafts. This takes place through intervention. Specific gears can be connected to the input and output shafts with a dog clutch.


The principal function of the gears is the power transfer between the shafts. The main shaft operates at an acceleration that is lenter than the counter shaft and vice versa when the gear ratios are more than one. The reverse and forward gear arrangements are available.

Line Diagram of Constant Mesh Gearbox

The line diagram of Constant Mesh Gearbox is shown below.

Working of Constant Mesh Gearbox

  • When the dog clutch is engaged with different gears of main shaft different gear ratios are obtained as gears of main shaft are always paired with gears of counter shaft to form different gear ratios.
  • If the dog clutch is not in contact with any gear of main shaft the gears of main shaft rotates freely and does not rotates the main shaft as they are connected with main shaft using bearings.
  • The main shaft rotates only when one of the dog clutch is engaged with any of the gear of the main shaft.
  • Reverse gear is obtained in this gearbox using the same technique that was in sliding gearbox i.e using the idle gear between main shaft gear and counter shaft gear.


  • First Contsant Mesh Gearbox are quiter because helical or herringbone gears can be used in this gearbox instead of spur gears.
  • Since the gears are engaged with the aid of using canine clutches, if any harm takes place while attractive the gears, the canine unit individuals get broken and now no longer the gear wheels.


  • It is less efficient than the others due to higher mesh teeth. Skill is required for it.
  • The double clutch mesh is required. This is required to have the spinning movements of the shaft.


  • Constant mesh gearbox become in particular utilized in farm trucks, motor motorcycles and heavy machinery.
  • It is likewise utilized in vehicles like Ford Model T.
  • Constant Mesh Box become used in motor motorcycles earlier than the creation of synchromesh gearbox in 1928 through General Motors.


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