What Is the Difference between Constant and Sliding Mesh in a Manual Transmission?

By Mister Transmission

Driving a stick? Get to know more about the gearbox that powers your car or truck

The history of manual transmissions and their evolution is fascinating. For instance, at one time, your car’s manual transmission included either a sliding-mesh gearbox or a constant-mesh gearbox.

A manual transmission sliding mesh is typically found in older vehicles. It is, in fact, one of oldest types of gearbox. To shift between different speeds using a sliding-mesh gearbox, the gears on the main shaft are shifted right or left for meshing them with the appropriate gears on the counter shaft (this is where the phrase ‘shifting gears’ comes from).

The problem with a sliding-mesh gearbox is when changing gears, the speeds of the input and output shafts must be matched first. Otherwise, the sliding dog teeth of the meshing gearwheels do not align, and they “crash” into one another. That is why this type of gearbox is alternatively referred to as a ‘crash box’.

A manual transmission constant mesh, meanwhile, is commonplace in newer manual transmissions – notably those in large trucks and farm vehicles. All of the gears mesh together simultaneously and at all times. In other words, the gears rotate freely on the main shaft, and the gear ratios are selected by clutches that connect them to shafts to power your vehicle.

Why a Constant-Mesh Gearbox Is Your Better Option

A sliding-mesh gearbox may be mechanically efficient, but the noise it generates when changing gears, and the difficulty that was involved when changing gears left much to be desired.

In comparison, the advantages of a constant-mesh gearbox include:

  • The gears used in a manual transmission constant mesh are helical and double helical and are quieter during operation
  • Because the gears in a constant-mesh gearbox are in constantly meshing, it’s less likely to damage the gear teeth, and there’s typically less wear on the gears
  • If a driver makes a “bad” change in gears, any damage that may occur will be limited to the dog clutch

The Synchro-Mesh Gearbox Comes to the Fore

For stick-shift enthusiasts, though a manual transmission constant mesh was an improvement over the sliding-mesh gearbox, drivers still required tremendous skill to operate them. That gave way to the synchro-mesh gearbox, a unit that has many similarities to its constant-mesh predecessor since the gears are always engaged. The exception is the inclusion of a cone clutch that sits between the dog clutch and gears. That means motorists no longer have to trouble themselves with the necessity of double declutching as they would using a constant-mesh gearbox.

 

Are you experiencing transmission troubles or have questions about your vehicle’s transmission? Visit the Mister Transmission location nearest you and get the expert help you need.

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Frank Matchett - You fit our vehichle (Toyota Celica) into the Coquitlam Shop so quickly on Monday, June 29th. I am from Kamloops. This was during Canada Day week too. You found a transmission on Vancouver Island and even offered to pick it up yourself if possible. You personally dropped me off and picked me up at the location I was staying at on Port Moody. I so appreciated that kindness. You went above and beyond and kept me, reassured that I would be home on Thursday. My husband was not with me yet you communicated the updates with both him & myself (he was in Kamloops.) You were wonderful with your communication, swiftness in finding the part, I\'m grateful that you fit my car in during this holiday week & your kindness to drop me off & pick me up was so appreciated. So thankful for all that you did Frank Matchett. Sincerely - Mrs. K Devlin
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