03-07-29-004H Manual Transmission Operating Characteristics - (May 30 2012) Manual - part 2
Backlash noise is created when changing engine or driveline loading. This can occurwhen accelerating from a stop, coming to a stop, or applying and releasing the throttle(loading and unloading the driveline). This will vary based on vehicle type, buildvariations, driver input, vehicle loading, etc. and is created from the necessaryclearance between all of the mating gears in the transmission, axle(s) and transfercase (if equipped).
Shift effort will vary among different style transmissions and synchronizer designs.Usually the more heavy duty the transmission, the higher the shift effort becauseof the increased mass of the components. Shift effort can also be higher in cold weatherbecause the fluid will be thicker. Medium duty transmissions will not shift as quicklyas a Corvette transmission. To reduce shift effort, do not attempt to rush the shift– allow thesynchronizers to work as designed. Shifting harder will only increase the chance ofrushing past the synchronizer leading to grinding while shifting.
Some light duty truck transmissions in 1st gear (creeper-gear) and reverse gears invarious transmissions, along with all gears in some medium duty transmissions, maybe non-synchronized. This means there is not a mechanism to match input and outputshaft speeds to allow for a smooth shift. This function is left up to the driver.This can be noticed if a shift into 1st or reverse is attempted while the vehicleis rolling or before theinput shaft stops rotating leading to a gear grind. The grinding can be reduced bycoming to a complete stop and pausing for a moment before shifting into the 1st orreverse gear. Some slight grinding can be expected. In medium duty non-synchronizedtransmissions, the driver must match input shaft (engine) speed to output shaft (driveshaft)speed with every shift. This can be accomplished by double clutching, or by usingother methods. If thedriver is not able to perform this function properly, there will be gear grindingwith each improperly completed shift. Driver training may be required to correct thiscondition. Clutch brakes are used in medium duty non-synchronized transmissions toallow a shift into gear at a stop. The clutch brake is used to stop the input shaftfrom spinning, allowing a shift into gear at a stop without grinding. The clutch brakeis activated by pressingthe clutch pedal all the way to the floor. When the clutch brake is used, it is possibleto have a blocked shift with the vehicle stationary. If this occurs, engage the clutchslightly to rotate the input gear to allow the shift.