Jeep Cherokee (XJ): Description and operation

Propeller shaft

DESCRIPTION

A propeller shaft (Fig. 2) is the shaft which connects the transmission/transfer case to the axle differential.

This is the link through which the engine power is transmitted to the axle.

The propeller shaft is designed and built with the yoke lugs in line with each other which is called zero phasing. This design produces the smoothest running condition, an out-of-phase shaft can cause a vibration.

Tubular propeller shafts are balanced by the manufacturer with weights spot welded to the tube.

PRECAUTIONS

Use the exact replacement parts when installing the propeller shafts. The use of the correct replacement parts helps to ensure safe operation. All fasteners must be torqued to the specified values for safe operation.

Also make alignment reference marks (Fig. 1) on the propeller shaft yoke and axle, or transmission, yoke prior to servicing. This helps to eliminate possible vibration.

CAUTION: Do not allow the propeller shaft to drop or hang from any propeller shaft joint during removal. Attach the propeller shaft to the vehicle underside with wire to prevent damage to the joints.

OPERATION

The propeller shaft must operate through constantly changing relative angles between the transmission and axle when going over various road surfaces. It must also be capable of changing length while transmitting torque. The axle rides suspended by springs in a floating motion.This is accomplished through universal joints, which permit the propeller shaft to operate at different angles. The slip joints (or yokes) permit contraction or expansion (Fig. 2).

Fig. 1 Reference Marks on Yokes

Before undercoating a vehicle, the propeller shaft and the U-joints should be covered to prevent an out-of-balance condition and driveline vibration.

CAUTION: Use original equipment replacement parts for attaching the propeller shafts. The specified torque must always be applied when tightening the fasteners.

Propeller shaft joints

DESCRIPTION

Two different types of propeller shaft joints are used:

•  Single cardan universal joint (Fig. 3)
•  Double cardan (CV) universal joint (Fig. 4)

None of the universal joints are serviceable. If one becomes worn or damaged, the complete universal joint assembly must be replaced.

Fig. 2 Propeller Shafts

1 - FRONT AXLE
2 - FRONT PROPELLER SHAFT
3 - TRANSFER CASE
4 - BOOT
5 - REAR AXLE
6 - STRAP
7 - REAR PROPELLER SHAFT
8 - STRAP

Fig. 3 Single Cardan Universal Joint

1 - NEEDLE BEARING
2 - BEARING CAP
3 - SEAL
4 - SPIDER
5 - NEEDLE BEARING
6 - BEARING CAP
7 - RETAINING CLIP
8 - YOKE
9 - SEAL

Propeller shaft joint angle

DESCRIPTION

When two shafts come together at a common joint, the bend that is formed is called the operating angle.

The larger the angle, the larger the amount of angular acceleration and deceleration of the joint. This speeding up and slowing down of the joint must be cancelled to produce a smooth power flow.

OPERATION

This cancellation is done through the phasing of a propeller shaft and ensuring that the proper propeller shaft joint working angles are maintained.

A propeller shaft is properly phased when the yoke ends are in the same plane, or in line. A twisted shaft will make the yokes out of phase and cause a noticeable vibration.

When taking propeller shaft joint angle measurements, or checking the phasing, of two piece shafts, consider each shaft separately.

Ideally the driveline system should have;

•  Angles that are equal or opposite within 1 degree of each other.
•  Have a 3 degree maximum operating angle.
•  Have at least a 1/2 degree continuous operating (propeller shaft) angle.

Fig. 4 Double Cardan (CV) Universal Joint

Propeller shaft speed (rpm) is the main factor in determining the maximum allowable operating angle.

As a guide to the maximum normal operating angles refer to (Fig. 5).

Fig. 5 Maximum Angles And Propeller Shaft Speed