Auto Questions: How Manual Transmissions Work

Learn the mechanics behind manual transmissions and how to drive more smoothly and safely.

Manual transmissions shift by means of shifter forks. The shifter forks ride in a groove that is cut into a synchronizer assembly and sliding gear. The shifter forks are connected to the cam and shaft assembly in a vehicle. There are spring-loaded steel balls that pop into the notches cut in the cam assembly. This holds the shifting mechanism so that it stays in whatever gear is selected by the driver. The shaft assembly passes through the housing and is then fastened to the shift levers.

Older vehicles that have three-speed transmissions have shift levers that can be operated through the shift linkage. The shift linkage is what is attached to the steering wheel's shift controls. On newer vehicles, the manual transmission uses a console or floor-mounted stick shift. The late models of four, five or six-speed transmissions have shift forks that operate by means of a floor stick shift. The floor stick shift actually enters the housing of the transmission where there are sliding shift fork rails engaged. Other floor stick shift designs will use linkage or cables, while other shift sticks are designed with a ball-like pivoted assembly.

When you shift a manual transmission, you should remember to always hesitate for a brief moment in the neutral gear. This is because the synchromesh unit always depends on a limited amount of friction in order for it to synchronize the speeds. If you hesitate for a moment and then shift smoothly into gear, the synchromesh unit has time for it to function properly.

When the transmission is in neutral, the input shaft is what drives the cluster gear. This then will turn the second speed gear so that there is no output power. The constant mesh of the second gear is actually revolving around the output shaft so that no power can be transmitted.

When you shift the transmission into first gear, the clutch needs to be depressed in order for the clutch disc to be released. When this happens, the input shaft and the cluster gear will no longer turn. The output sliding low gear will then shift forward so that it meshes with the cluster low gear. This is so that the cluster gear turns at a slow speed, but the output second gear does not mesh with the cluster gear during first gear shifting. It is the cluster low gear that turns the output shaft at a slow speed.

When the transmission is ready to be shifted into second gear, you will need to depress the clutch again in order to stop the flow of power to the engine. When this happens, the low sliding gear will move into the neutral position and then the second sliding gear will mesh with the cluster gear. You will then release the clutch so that the power flow to the engine is resumed, but with less torque multiplication.

Once the vehicle has reached and sustained a sufficient speed, you will need to depress the clutch once more. The sliding second gear will then move forward until the splined recess is able to slip over the splined stub along the input shaft. The low sliding gear will then become unmeshed. Once you release the clutch, the transmission will go into direct drive with no torque multiplication needed.

When you need to put the transmission into reverse, the sliding gear will need to be placed in the neutral position. The low reverse sliding gear will then move back until it is able to engage itself with the reverse idler gear. When the reverse idler gear revolves, it revolves in the same direction as the input shaft's motion. This will allow a reverse rotation to the output shaft. The output shaft will then cause the vehicle to drive backward.

When shifting the vehicle, always remember that speed shifting is not recommended on any manual transmission unless the vehicle has been modified to withstand such abuse. When a driver does speed shifting, it causes the synchronizer cones to wear faster because of the excessive friction being applied. It will also damage the gears and the drive train.

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