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.

(2)Three-joint type

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.

HINT:

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.

HINT:

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.

The drive shaft/axle shaft transmits the drive force to the wheel. 1. Drive shaft (Independent suspension type) They must have a mechanism which absorbs changes in the length of the drive shafts accompanying the up and down movements of the wheels. In the case of FF vehicles, since the same wheels are used for steering and for driving, they must be capable of maintaining the same operating angle while the front wheels are being steered, and they must rotate the wheels at uniform speeds. 2. Axle shaft (Rigid suspension type) The right and left wheels are connected to the axle shaft. The axle housing supports the weight of the vehicle while also holding the differential in its center.

Construction and Operation

1. Constant velocity joints

The constant velocity joints prevent a rotation difference from occurring between the drive shaft and driven shaft no matter what the angle of the joint. These joints are mainly used in the drive shafts of vehicles with independent suspensions. There are various kinds of different types of constant velocity joints.

(1) Rzeppa (Birfield) joint The inner race fits into the bowl-shaped outer race, with six steel balls held by a ball cage between them. The construction of this system is simple and its transmission capacity is great. This type of joint is used on the drive shaft tire side.

(2) Principle of constant velocity joint (Rzeppa joint) A special curvature is provided on the ball seat in such a way that intersecting point (O) of the centerlines of the drive and driven shafts are always on the line connecting the center (P) of each steel ball. As a result, the angular velocity (speed of rotation through an angle) of the drive shaft is always identical to that of the driven shaft. (1/3)

2. Tripod joint In this joint,

there is a tripod with three trunnion shafts on the same plane. Three rollers are fitted on these trunnions, and fitted to each of the rollers are three tulips with grooves which are parallel to each other. The construction of this system is simple and it is inexpensive. Generally, this type of joint can move in the axial direction. This type of joint is used on the drive shaft differential side.

3. Double-offset constant velocity

The construction of this type of joint closely resembles that of the Rzeppa (Birfield) type, but it can slide in the axial direction. The outer and inner surfaces of the ball cage are offset axially from each other.

4. Cross-groove constant velocity

This is a small, light-weight joint in which the ball grooves of the outer race and those of the inner race are set at angles to each other. These are two types, one which slides axially, and one which dose not.

SERVICE HINT:

If there is a crack in dust boots of the constant velocity joint, the grease will deteriorate and flow out, which will cause abnormal sounds and make it impossible to drive. Since there are various types of boot clamps that hold the drive shaft boots, refer to the Repair Manual and handle them correctly. The type and amount of grease used inside the drive shaft boots varies depending on the model, so refer to the Repair Manual.

Drive Shaft Length

In the FF vehicles, differences in the length of the left and right drive shafts can also causes the steering wheel to jerk to one side or the vehicle to veer during quick starts or sudden acceleration. This phenomenon is known as “torque steer”. For this reason, some models use an intermediate shaft in combination with right and left drive shafts of the same length to prevent torque steer from occurring.

Center Differential and Transfer

1. Transfer

This transfer is a two-speed (Low- High) type. The center differential is located inside the low speed output gear of the output shaft. Power is transmitted to the center differential from the transmission via the input shaft, the high or low speed idler gear and the high or low speed output gear.

2. Power transmission

Low-speed Mode

3. Center differential

The center differential gear is the bevel gear type and the center differential limit control mechanism is the mechanical locking type. The center differential gear unit consists of two pinion gears. During straight-ahead driving, when there is no speed differential between front and rear wheels, the center differential pinion gears do not revolve. When a speed difference between the front and rear wheels occurs due to cornering, etc., the center differential pinion gears revolve, absorbing the speed difference.

4. Shift fork slide system

A shift fork slide system which uses a shift fork shaft to switch between the “L4″ range and the “H4″ range, and to carry out locking of the center differential, is used. Switching between low and high speeds is accomplished by the transfer lever, while locking of the center differential is accomplished electrically by a motor driven transfer shift actuator.

5.Transfer shift actuator

Drives motor and changes driving mode (“Free” or “Locked”) in accordance with signals from 4WD control relay.

<1>Motor control limit switch When the contact plate slides under the contact springs while turning with the rotation of the driven gear, the electrical connection between it and the contact springs changes, causing the motor to stop in the optimal position at all times.

<2>Spiral springs If the operating resistance of the front drive shift fork shaft is large, the rotational force of the motor is partially “stored” in these springs. Afterward, when the operating resistance is reduced, the spring force causes the front drive fork shaft to slide.

Center Differential Locking System

1. General

The center differential locking system mechanically locks the center differential, forcing power to be transmitted evenly to front and rear differentials. If any one of the wheels is stuck, the other three wheels also spin. Therefore, locking the center differential distributes power it equally to all four wheels and makes it possible to get out.

2. Components

The system consists of the following parts.

(1)Center differential lock indicator light Indicates condition (free or locked) of center differential to driver

(2)Center differential lock switch Switches center differential control mode between “Lock” and “Free”.

(3)Center differential lock indicator switch Detects that center differential is locked.

(4)”L4″ position switch Detects transfer shift lever position (“H” or “L”)

(5)Center differential lock control relay Locks or unlocks center differential depending on signals from various sensors.

(6)Transfer shift actuator (1/2) 1. Features of range switching mechanism The chart on the left shows in which conditions each position of the transfer shift lever and differential lock switch are used.

HINT:

When the transfer shift lever is in the “L” range position, the L4 position switch is on, so center differential lock control relay operates regardless of whether the differential lock switch is on or off, and the motor turns, causing the center differential to be locked.