The propeller shaft (on FR vehicles and 4WD vehicles) transmits power from the transaxle/transmission to the differential. The propeller shaft can move up and down in response to the road conditions and absorb the change of length by the spline. The propeller shaft is installed at a position that makes the differential lower than the transaxle/transmission, so it is sloped. For these reasons, the propeller shaft is designed in such a way that it transmits power smoothly from the transaxle/ transmission to the differential without being affected by such changes.
Construction and Operation
1. Propeller shaft
The propeller shaft is a lightweight hollow carbon steel tube which is strong against enough to resist twisting and bending. The propeller shaft is normally a single piece tube having two joints at both ends that form universal joints. Since there is little vibration at high speed, the three-joint type propeller shaft is used more often today.
(1) Two-joint type
The overall length of each segment of the two-joint type propeller shaft is relatively great. This means that, when the propeller shaft is rotating at a high speed, the shaft tends to bend slightly and vibrate more because of the residual imbalance.
The length per shaft of the two-piece, three-joint type propeller shaft is shorter and bending due to imbalance is therefore less. Vibration at high speeds is also reduced for the same reason.
(3) Center bearing
The center bearing supports the two parts of the propeller shaft in the middle, and is installed via a flange to the splines located at the end of the intermediate shaft. The center bearing itself, consists of the rubber bushing that covers the bearing which, in turn, supports the propeller shafts, and is fitted to the body by a bracket. Because of the fact that the propeller shaft is separated into two sections, vibration in the propeller shaft is absorbed by the rubber bushing to prevent vibration from reaching the vehicle body. As a result, vibration and noise from the propeller shaft in high speed ranges are reduced to an absolute minimum.
Before disassembling the center bearing, match marks must be made on the flange yoke and intermediate shaft to ensure accuracy when the flange yoke is assembled after servicing. If parts are assembled without reference to the match marks, vibration and/or noise may result when the vehicle is driven.
2. Universal joint
The purpose of the universal joint is to absorb the angular changes brought about by changes in relative positions of the differential in relation to the transmission, and in this way to smoothly transmit power from the transmission to the differential. Hooke’s joint Hooke’s joints are commonly used because of their simple construction and functional accuracy. One of the two yokes is welded to the propeller shaft, and the other yoke forms an integral part of a joint flange or a sleeve (slip joint). In order to prevent the bearing cup from flying off when the propeller shaft is turning at high speed, either a snap ring or a lock plate is used to fasten the bearing cup in the solid bearing cup type. The shell bearing cup type cannot be disassembled.
Flexible joint The straighter the centerline connecting the transmission, propeller shaft, and differential, the less vibration and noise that will occur. Therefore, in some of the latest FR passenger cars, a zero angle propeller shaft is used. Such a propeller shaft also has flexible joints to ensure less vibration and noise.
When removing and installing the propeller shaft: Since there is a shaft length adjusting mechanism, the adjusting nut should be loosened first before removing the propeller shaft. The bolts (A) inserted in the propeller shaft companion flange should not be removed. Be careful not to apply undue force to the flexible couplings when handling the propeller shaft, and make sure the transmission, propeller shaft, and differential are always straight when removing and reinstalling the propeller shaft. After installation, be sure to check the joint angles.
(2) Constant velocity joint A constant velocity joints transmits torque more smoothly than a Hooke’s joint, but is more expensive.