Mechanical Transmission/en

Diesel-mechanical vehicles are propelled by an onboard diesel engine and a mechanical transmission. The engine power is conveyed to the wheels using a gearbox, similar to that of large road vehicles.

By operating the throttle control, the driver adjusts fuel injection to the engine and thus the rotating speed of its crankshaft. Using a gearbox, the power from the engine is mechanically transmitted to the wheels. Gears are typically changed manually, by one or more transmission levers.

With the vehicle in first gear, adding throttle will propel it forward with relative ease, but it won't reach a high speed just yet. By shifting gears sequentially, the driver can make the vehicle reach higher speeds, but also have a gradually harder time accelerating. Gear ratios are designed to be used sequentially, so that the peak power of the engine is utilized as much as possible in each suitable gear, at all speeds.

Gear selection is typically done by operating a lever. Some vehicles may have multiple gear selectors, depending on the gearbox design and usage. To avoid damage when changing gears, throttle must be fully disengaged.

On vehicles with mechanical transmission the load on the wheels directly affects the engine. While diesel-mechanical vehicles have a fluid coupling to help prevent stalling at a standstill, they can still stall when under heavy load. For example, if the driver were to attempt taking off in too high of a gear, the engine wouldn't have enough power to propel the vehicle, its rotational speed would drop below the minimum tolerance, and stalling would occur.

In order to appropriately time the gear changes while on the move, it is necessary to monitor the RPM gauge. Upshifting should be done when the needle comes close to the red line, and downshifting should be done when the needle is close to the idle RPM, and the engine is losing power.

Any load on the fluid coupling, either from the wheels or from the engine trying to accelerate or slow down, will heat up the transmission fluid. Overheating is a critical danger to beware of, as, depending on the session difficulty settings, it could cause catastrophic damage to the vehicle.

See also: Internal Combustion Engine, Powertrain Overheating, Mechanical Powertrain Damage, Throttle, Hydraulic Transmission, Engine & Compression Brake, Difficulty