Inoperative Conditions
ANALYSIS OF INOPERATIVE CONDITIONSIf the axle fails to operate, there will be broken or jammed-up parts. Analyze why the parts have broken to prevent the condition from recurring.
BROKEN AXLE SHAFT
Inspect a broken axle shaft for a twist in the spline next to the break.
Breaks that occur away from the spline or that are not accompanied by a twist in the spline may be caused by forging flaws and/or fatigue of the axle shaft.
Conditions that can cause a broken axle shaft include forging flaws or excessive impact load to the axle shaft as a result of a collision or other factors.
BROKEN PINION STEM
The drive pinion stem can break at any time if the differential pinion bearing preload is not set up properly. If there is no preload, the differential pinion bearing will turn relative to the axle shaft. This galls the roller shaft and generates heat which can draw the temper away from the shaft.
Too much preload also generates bearing heat with the same result. The break normally occurs between the two differential pinion bearings.
SHOCK FAILURES
Shock failure is another common type of carrier failure. This failure results from a rapidly applied load or force that exceeds the strength of the carrier component. If the failed part separates into two or more pieces, the operator will usually realize it immediately. If the part is only cracked, however, the operator may not be aware of the damage until sometime later. The failure may occur even under normal operating conditions. There are a number of operating conditions which can result in shock failure:
- Hitting Dry Pavement With A Spinning Wheel
This can induce a severe shock load in the axle and drivetrain. When the wheel is spinning, the axle components are rotating at high speed. As the wheel contacts a dry surface or one with greater traction, it slows down very rapidly. If the deceleration is great enough, forces sufficient to exceed the strength of the axle may result, and cause a failure.
- Missing A Shift
A missed shift is especially damaging when the operator is downshifting on a down grade. The impact to the coast side of the gearset can cause a failure.
- Popping The Clutch
A certain amount of torque is required at the drive wheels to start a vehicle moving. If the wrong transmission gear is selected, there may not be enough torque available at the rear wheels. In this situation the driver may speed up the engine and rapidly release the clutch, rather than selecting a lower gear. This severe load can result in a shock failure.
LUBRICATION FAILURES
Another common cause of axle failures originates with the lubricant, or with lubricant change practices. The lubricant that protects the axle components has three key functions:
^ to reduce friction between parts
^ to carry heat away from parts
^ to carry dirt and wear particles away from parts
When a lubrication failure occurs, it is generally the result of improper maintenance and had its roots in one of three basic problem areas:
^ low lubricant level
^ improper type of lubricant or lubricant with depleted additives
^ contaminated lubricant