What is the function of the rear axle?
A rear axle has to change the axis of rotation of the propeller shaft to that of the rear wheels. It provides a reduction speed from the propeller shaft to the two axle half shafts, and it has also to provide a differential mechanism for allowing a different speed of rotation of the two rear wheels when the vehicle is cornering.
What is the commonest early symptom of trouble in a rear axle assembly? The first indication that all is not well is the production of excessive noise. The type of noise produced often gives a very good indication of the nature of the trouble.
If the noise is a hum, mainly heard when the "car is driving the engine", i.e., when the foot is removed from the accelerator, it is an indication that the pinion is not meshing deeply enough in the crown wheel. If the noise is a grinding one and is heard most loudly when the car is accelerated, it is a sign that the pinion is meshing too deeply in the crown wheel.
What should be looked for when examining the rear axle?
1) Wear in oil seals
2) Wear or pitting of bearings
3) Wear on splines of axle shafts
4) Worn or damaged teeth on gears and pinions. Slight pitting or burrs can be stoned off teeth but badly worn or scored teeth indicate need for renewal.
5) Straightness of axle shafts.
6) Wear on differential spider or spindle journals
7) Runout of crown wheel
8) Burrs between mating surfaces e.g., crown wheel and differential case
9) Alignment of the axle housing.