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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Ab H
I just wanted to say that the Orillia Mr T is amazing! Christina is very pleasant to deal with. They tested my car and told me the power issue and engine light was an engine problem and that the transmission was in good shape. They also said it was probably a turbo related problem. I had my mechanic fix the issue which was a cracked air intake pipe for the turbo. It's great to deal with a very professional and honest operation!
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Great stuff. Very nice people . Do good job.
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Fast, friendly, efficient! Came in with a blown. Clutch. He got me in Same day and had my truck back to me in a few days! Definitely recommend this guy to anyone in the arena that needs transmission work! 👍🏻👍🏻
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I was driving into the city from out of town when I suddenly got warning lights. I called and spoke to Tanya who was so helpful, she worked to get me in quickly. The team diagnosed the problem quickly, ordered in the part and had the work done within 24 hours. I really felt they went out of their way for me because they knew I was in a tough position. Excellent service! Thank you!
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I could not be happier with the service that I received, this is a first class shop. When I took my sons car in they went above and beyond to help us out not only with the transmission but also the engine, what a fantastic group they have. I strongly recommend this shop to anybody with transmission issues I’m sure you will be very satisfied as was I. Right from Denise in front office to her husband Sean and and the crew in the shop you have my utmost thanks. Dave Traves
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