The propeller shaft has the yoke lugs (ears) in line and in phase with each other. This design produces a smooth running shaft.

An out-of-phase propeller shaft causes vibration. The propeller shaft generates vibration from speeding up and slowing down each time the universal joint turns. This vibration is like someone snapping a rope and watching the wave reaction flow to the end.

An in-phase propeller shaft is like two persons snapping a rope at the same time, then watching the waves meet and cancel each other. A total cancellation of vibration produces a smooth flow of power in the driveline. The phasing of a propeller shaft is formed between the front and the center universal joints. Before removal, reference mark the front and rear propeller shafts. Reinstallation will ensure proper phasing. Some splined propeller shaft slip yokes are keyed to ensure proper phasing.