vehicle  with  rear-wheel  drive.  A  few  of  these  advan- tages are the following: Improved  efficiency  and  reduced  drive  train weight Improved traction on slippery surfaces because of increased weight on the drive wheels Increased   passenger   compartment   space   (no hump in floorboard for rear drive shaft) Less unsprung weight (weight that must move with  suspension  action),  thereby  providing  a smoother ride Quieter  operation  since  engine  and  drive  train noise  is  centrally  located  in  the  engine  com- partment Improved safety because of the increased mass in front of the passengers Most transaxles are designed so that the engine can be transverse (sideways) mounted in the engine com- partment. The transaxle bolts to the rear of the engine. This  produces  a  very  compact  unit.  Engine  torque enters  the  transaxle  transmission.  The  transmission transfers  power  to  the  differential.  Then  the  differ- ential turns the drive axles that rotate the front wheels. Both  manual  and  automatic  transaxles  are available. Manual transaxle uses a friction clutch and a standard   transmission-type   gearbox.   An   automatic transaxle   uses   a   torque   converter   and   a   hydraulic system to control gear engagement. MANUAL  TRANSAXLE A  manual  transaxle  uses  a  standard  clutch  and transmission.   A   foot-operated   clutch   engages   and disengages the engine and transaxle. A hand-operated shift  lever  allows  the  operator  to  charge  gear  ratios. The  basic  parts  relating  to  a  manual  transaxle  are  as follows: Transaxle Input Shaft—main shaft splined to the clutch disc turns the gear in the transaxle. Transaxle Input Gears—either freewheeling or fixed gears on the input shaft and meshes with the output gears. Transaxle  Output  Gears—either  fixed  or  free- wheeling gears driven by the input gears. Transaxle Output Shaft—transfers torque to the ring gear, pinion gears, and differential. Transaxle  Synchronizers—splined  hub  assem- blies  that  can  lock  freewheeling  gears  to  their shafts  for  engagement. Transaxle   Differential—transfers   gearbox torque to the driving axle and allows the axles to turn at different speeds. Transaxle  Case—aluminum  housing  that encloses and supports parts of the transaxle. The  manual  transaxle  can  be  broken  up  into  two separate units—a manual transaxle transmission and a transaxle   differential.   A   manual   transaxle   trans- mission provides several (usually four or five) forward gears  and  reverse.  You  will  find  that  the  names  of shafts,  gears,  and  other  parts  in  the  transaxle  vary, depending  on  the  location  and  function  of  the components. For example, the input shaft may also be called the main shaft, and the output shaft is called the pinion shaft because it drives the ring and pinion gear in  the  differential.  The  output,  or  pinion,  shaft  has  a gear or sprocket for driving the differential ring gear. The  clutch  used  on  the  manual  transaxle  trans- mission is almost identical to the manual transmission clutch for rear-wheel drive vehicles. It uses a friction disc  and  spring-loaded  pressure  plate  bolted  to  the flywheel. Some transaxles used a conventional clutch release  mechanism  (release  bearing  and  fork);  others use a long pushrod passing through the input shaft. The  transaxle  differential,  like  a  rear  axle  differ- ential,  transfers  power  to  the  axles  and  wheels  while allowing one wheel to turn at a different speed than the other. A small pinion gear on the gearbox output shaft or  countershaft  turns  the  differential  ring  gear.  The ring gear is fastened to the differential case. The case holds  the  spider  gears  (pinion  gears  and  axle  side gears) and a pinion shaft. The axle shafts are splined to the differ-ential side gears. AUTOMATIC  TRANSAXLE An automatic transaxle is a combination automatic transmission  and  differential  combined  into  a  single assembly. The basic parts of an automatic transaxle are as follows: Transaxle  Torque  Converter—(fluid-type  clutch that slips at low speed but locks up and transfers engine power at a predetermined speed; couples and  uncouples  engine  crankshaft  to  transmission input  shaft  and  gear  train). 4-42