A motor coupler is a device that connects an electric motor to the drive system on an appliance, such as a washing machine. Commonly designed as a three-piece component, a motor coupler uses two drive plates cushioned by a rubber shock absorber. The typical motor coupler is designed to slip fit onto the motor's output shaft and does not require a fastener, in most cases, to remain in place. The coupler inside of an appliance acts in the same capacity as the drive shaft does in an automobile as it transfers the power of the motor to the transmission.
By placing a rubber disk between the two nylon drive gears of the motor coupler, the shock of the motor switching on is absorbed instead of damaging the output shaft of the motor or the input shaft of the transmission. In an appliance, such as a washing machine, this rubber also absorbs the torque of a loaded washing drum as the motor switches off. The rubber is allowed to stretch as the heavy drum tries to continue rotating when the motor is turned off when the wash cycle ends. Conversely, the rubber stretches slightly as the motor switches on and the drum is filled with water. This repeated stretching is typically what causes the motor coupler to wear out or break.
It is very critical that the entire motor coupler be changed when servicing a broken coupler. Often, only one tooth will be broken off of one of the drive gears, tempting a repair person to replace only the broken piece. The entire coupler has experienced numerous cycles of hard work, stretching and contracting prior to the tooth breaking off. This wear has also taken its toll on the unbroken parts and will result in a broken tooth if it is not replaced as a unit at the time of service. In some circumstances, a commercial-grade coupler is available to be switched into place in a home washing machine; this is typically overkill, but it can add longevity to the coupler.
There is no fastener used in the retention of the coupler. The motor coupler is simply sandwiched between the motor and the transmission in the machine. The reason that no fastener is needed to secure the coupler to the shafts is the cut of the shafts and the center drive hub of the coupler. The coupler fits onto a hex shape machined into the shaft on both the transmission and the motor, thereby eliminating any possibility of slip between the components.