CHAPTER 5 DRIVE LINES, DIFFERENTIALS, DRIVE AXLES, AND POWER  TRAIN  ACCESSORIES INTRODUCTION Learning   Objective:  Identify   the   components   and explain the functions and the maintenance procedures for  a  drive  line  assembly,  differentials,  drive  axles,  a transfer  case,  and  a  power  takeoff  unit.  Describe  the different types of universal and constant velocity joints. Explain the adjustments and measurements of the ring and  pinion  gears.  Describe  the  procedures  for  removing and replacing axle bearings and seals. One  important  function  of  the  power  train  is  to transmit  the  power  of  the  engine  to  the  wheels.  In  a simple situation, a set of gears or a chain could perform this   task,   but   automotive   vehicles   usually   are   not designed  for  such  simple  operating  conditions.  They are  designed  to  have  great  pulling  power,  move  at different   speeds,   operate   forward   and   reverse,   and travel  on  rough  as  well  as  smooth  surfaces.  To  meet these  widely  varying  conditions,  a  number  of  units have been added. In this chapter we will discuss drive lines,  differentials,  drive  axles  (rear  and  front  drive), and power train accessories (transfer cases and power takeoffs). DRIVE  LINE  ASSEMBLY Learning   Objective:   Identify   the   parts   and   the functions of different types of drive lines. Describe the different types of universal joints. The   drive   line   assembly   has   several   important functions. It must perform the following: Send turning power from the transmission to the rear axle assembly. Flex and allow up-and-down movement of the rear axle assembly. Provide a sliding action to adjust for changes in drive line length. Provide a smooth power transfer. The  assembly  provides  a  path  through  which power is transmitted from the transmission to the drive axle   assemblies   or   auxiliary   equipment.   Vehicles, having  a  long  wheelbase,  are  equipped  with  a  drive shaft  that  extends  from  the  transmission  or  transfer case to a center support bearing and a drive shaft that extends  from  the  center  support  bearing  to  the  rear axle. The drive line assembly (fig. 5-1) consists of the following: SLIP YOKE—connects the transmission output shaft  to  the  front  universal  joint. FRONT  UNIVERSAL  JOINT—the  swivel connection that fastens the slip yoke to the drive shaft. DRIVE  SHAFT—a  hollow  metal  tube  that transfers turning power from the front universal joint to the rear universal joint. REAR  UNIVERSAL  JOINT—a  flex  joint  that connects the drive shaft to the differential yoke. REAR  YOKE—holds  the  rear  universal  joint and transfers torque to the gears in the rear axle assembly. SLIP YOKE (JOINT) The  type  of  transmission  (manual  or  automatic) determines how the slip joint is connected to the drive shaft.  On  a  manual  transmission,  the  slip  yoke  is splined to the drive shaft with the yoke for the universal joint directly behind the transmission or transfer case, whereas,   with   the   automatic   transmission,   the   slip yoke  is  splined  to  the  output  shaft.  Either  way  they serve   the   same   purpose—to   provide   the   necessary telescopic   action   for   the   drive   shaft.   As   the   axle housing  moves  forward  and  backward,  the  slip  joint gives  freedom  of  movement  in  a  horizontal  direction and yet is capable of transmitting rotary motion. The slip yoke used with an automatic transmission has the outer diameter machined smooth. This smooth surface provides a bearing surface for the bushing and rear oil seal in the transmission. The transmission rear oil  seal  rides  on  the  slip  yoke  and  prevents  fluid leakage  out  of  the  rear  of  the  transmission.  The  seal also keeps dirt out of the transmission and off the slip yoke. 5-1