this assembly a true full-floating axle, but nevertheless, it is called a floating axle. A true full-floating axle transmits only turning effort or torque.

Driving Wheels

Wheels attached to live axles are the driving wheels. The number of wheels and number of driving wheels is sometimes used to identify equipment. You, as a mechanic, may identify a truck by the gasoline or diesel engine that provides the power. Then again, you may refer to it as a bogie drive.

Wheels attached to the outside of the driving wheels make up DUAL WHEELS. Dual wheels give additional traction to the driving wheels and distribute the weight of the vehicle over a greater area of road surface. They are considered as single wheels in describing vehicles; for example, a 4 x 2 could be a passenger car or a truck having four wheels with two of them driving. A 4 x 4 indicates a vehicle having four wheels with all four driving. In some cases, these vehicles will have dual wheels in the rear. You would describe such a vehicle as a 4 x 4 with dual wheels.

A 6 x 4 truck, although having dual wheels in the rear, is identified by six wheels, four of them driving. Actually, the truck has ten wheels but the four wheels attached to the driving wheels could be removed without changing the identity of the truck. If the front wheels of this truck were driven by a live axle, it would be called a 6 x 6.

The tracks on tracklaying vehicles are driven in much the same manner as wheels on wheeled vehicles. Sprockets instead of wheels are driven by live axles to move the tracks on the rollers. These vehicles are identified as either full-track, half-track or vehicles that can be converted.

Full-Track Vehicles

Full-track vehicles are entirely supported, driven, and steered by two tracks that replace all wheels.

SERVICE AND MAINTENANCE

There are very few adjustments to be made in power trains during normal operation. Most of your duties concerned with power trains will be limited to preventive maintenance. You will be working with the disassembly, repair, and reassembly of transmissions, rear axles, and propeller shaft assemblies when they break down. You will also inspect these units for indications of major repairs needed. Major repairs can be reduced by proper lubrication and periodic inspection of gear cases, propeller shafts, and wheel bearings.

Proper lubrication depends upon the use of the right kind of lubricant which must be put in the right places in the amount specified by the LUBRICATION CHARTS. The charts, provided with the vehicle, will also show what units in the power train will require lubrication, and where they are located. These units are similar to the ones described and illustrated in this chapter.

In checking the level of the lubricant in GEAR CASES and before you add oil, keep these two important points in mind: first, always carefully wipe the dirt away from around the inspection plugs and then use the proper size wrench to remove and tighten them. A wrench too large will round the corners and prevent proper tightening of the plug. For the same reason, never use a pipe wrench or a pair of pliers for removing plugs. Second, be sure the level of the lubricant is right-usually just below or on a level with the bottom of the inspection hole. Before checking the level, allow the vehicle to stand for a while on a level surface so the oil can cool and find its own level. Oil heated and churned by revolving gears expands and forms bubbles. Although too little oil in the gearboxes is responsible for many failures of the power train, do not add too much gear lubricant. Too much oil results in extra maintenance.

Excessive oil or grease can find its way past the oil seals or gear cases. It maybe forced out of a transmission into the clutch housing and result in a slipping clutch; or it may get by the rear wheel bearings from the differential housing to cause brakes to slip or grab. In either case, you will have extra work to do. Always clean differential and live axle housing vents to prevent pressure buildup (caused by heat), which can result in leaking seals.

UNIVERSAL JOINTS and SLIP JOINTS at the ends of propeller shafts are to be lubricated if fittings are provided. The same holds true for WHEEL BEARINGS. Some of these joints and bearings are packed with grease when assembled; others have grease fittings or small plugs with screwdriver slots that can be removed for inserting grease fittings. Do not remove these plugs until you consult the manual for instructions.

Some passenger cars and trucks have a leather boot or shoe covering the universal and slip joint. The boot prevents grease from being thrown from the joint and it also keeps dirt from mixing with the grease. A mixture