How does gear selection work in a manual transmission?

The purpose of a transmission is to allow the engine to operate at its optimum efficiency while transmitting the power to the vehicle’s wheels. In a manual transmission, gears are changed by the vehicle operator, which is achieved by using a clutch to disengage the engine and a gear stick to change the gear. The number of gears in a manual transmission has traditionally been 4 or 5, but most modern manual transmissions now have 6 gears to enable better efficiency.

The animation below demonstrates how gear selection works in a 5-speed manual transmission.

Manual Transmission fluids (MTF) are essential to the smooth operation of these complex pieces of engineering. Basic gear fluids are no longer sufficient to meet the lubrication needs of a modern manual transmission. A dedicated MTF based on a carefully formulated Additive Package is essential to ensure gears and bearings are protected and components such as synchronisers operate smoothly and efficiently. 

While gear and bearing protection is critical in a manual transmission, MTF Additive Packages differ significantly from Axle Additive Packages. MTF Additives typically contain less EP (Extreme Pressure) chemistry and more anti-wear chemistry due to the different gear types used in the transmission, which are generally operating under different lubrication regimes due to more rolling and less sliding in the gear tooth contact. Using less EP (Extreme Pressure) additives also ensures that the Manual Transmission Fluid is compatible with Brass and Sinter alloys found within many transmissions.

In addition to gear protection, the MTF Additive must provide a suitable level of friction to enable the synchronisers within the transmission to operate. Synchronisers are at the heart of the transmission and allow the user to change gears. 

The role of an MTF is made more challenging by the increasing power density trend. As hardware is made smaller and lighter to reduce overall vehicle weight in the pursuit of efficiency targets, operating temperature, and thermal stresses on the lubricant increase. A modern MTF additive package must ensure a high level of oxidation and thermal control to maintain the efficient operation of components within the transmission.

Therefore, a careful selection of additive components is required to give the right mix of performance from the additive package and meet any additional economic and environmental requirements.

Afton’s range of gear additives are formulated to meet these increasingly complex manual transmission designs and severe operating conditions. In addition, our portfolio encompasses a variety of customer needs, including bespoke and marketable claims, field performance demonstration, base stock compatibility, and cost efficiency requirements, to name a few. They meet the very latest performance requirements for extended drain, fuel economy, and temperature stability.

All this information is now available to you on your iPhone and iPad via our app! This is the first digital edition of the Getting into Gear™ book and has been designed as an interactive reference tool for our oil company partners, our distributors, OEMs, and our employees. Indeed, it is for anyone Getting into Gear™.

It includes other detailed animations and gives readers access to a wealth of information covering the different types of gears, applications, market trends in hardware and fluids, and the additives and specifications for manual transmissions and axles.

Complete the form below to request a printed copy of the Getting into Gear™ Book.