For special applications, the truck's frame strength and proper gear capacity need to checked to make sure it can handle the gross vehicle weight. Some applications and suspensions require a thicker axle housing wall for added durability. Automatic traction control or driver-controlled differential lock may be required for off-road applications.
• Transfer cases - These direct power to both ends of an axle through separate driveshafts. Transfer cases are used for more than conventional power split and driveline drop. Many single-speed units are selected to provide additional features, such as PTO mountings to drive vehicle accessories, such as pumps, winches, etc.
Dependent on torque requirements, many transfer case configurations are selected to improve driveline angles and/or ground clearance, the officials say. Various transfer cases offer flexibility to reverse engine rotation into vehicle designs, as well as have feature options such as park brakes, power torque control and torque differentiation between front/rear axles.
Here again, ArvinMeritor officials counsel referring to the axle manufacturer's applications guides or contacting the transfer case manufacturer for the correct on-off-highway usage requirements to avoid a failure and the denial of a warranty for a condition that voids the warranty.
• Front drive axles - Similar to a rear drive axle, it is important to match these axles with the exact application of the vehicle. Determine whether the axle will be used in drive full-time or part-time. If used with the front axle engaged more then 20 percent of the time, a differential transfer case should be specified, suggest the officials.
ArvinMeritor officials also point out a number of other factors to be aware of with regard to engine and drivetrain performance and life:
• Vehicle and drivetrain performance can be impacted by improper use and specification of engine and driveline retarders. The amount of power and torque developed by such retarders needs to be calculated when specifying a drivetrain. Be certain not to use more brake retardation than is specified by the component and vehicle maker.
• Wide-base tires can affect bearing life. The officials recommend consulting tire dealers and manufacturers on these issues.
• Use lift axles properly to save on tire wear and to extend life of the drive axle. Overloading the drive axle - resulting in cracked housings - can be caused by too much vertical load and not employing the tag or pusher axle. One tip is to look for the sticker(s) on the cab door to understand all load limits.
• When spec'ing standard hubs (not the long-life package), it is a good idea to insist that the manufacturer install inner and outer bearing components from the same manufacturer.
• Know the difference in specifying and using a driver-controlled differential lock (DCDL), automatic traction control (ATC) and inter-axle differential (IAD) lock. A driver's behind-the-wheel performance can extend drivetrain life through the proper use these devices.
The driver-controlled differential lock positively locks the wheel differential to provide improved traction under adverse road conditions. The differential lock is controlled through an electric switch or air valve mounted in the cab.
The locking mechanism is air operated to engage a mechanical clutch that locks the wheel differential. It is spring operated to disengage the lock and permit the wheel differential to operate normally.
Automatic traction controls are integrated with antilock brake systems and electronic engine controls in such a way as to prevent loss of stability and control caused by excessive drive-axle wheel slip.
The inter-axle differential lock is a driver-controlled, air-actuated traction device that allows for speed differences between the forward and rear tandem axles, while providing equal pulling power from each axle of the tandem to help ensure that the vehicle maintains traction.
• Match tires on tandem wheel ends. For example, placing an older steer tire in a drive wheel position can make the inter-axle differential work harder and cause undue wear. Also, tires with different tread depths or air pressures can lead to a premature loss of axle life. Another result of mismatched tires is elevated lubricant temperatures and thus shorter lubricant and axle life.