1. Front-Wheel-Drive (Transaxle and CV Joint) Fundamentals
Chapter 77

2. Objectives
Describe differences between front- and rear-wheel drivetrains
Tell the names of parts of a transaxle
Trace the power flow through four- and five-speed transaxles

3. Introduction Most automobiles today have front-wheel drive
FWD car has transaxle
Drive axles extend to front wheels out of each side of transaxle
Each end of the drive axle is a CV joint
Transaxle can be either manual or automatic

5. Front-Wheel Drive Advantages
More efficient drivetrain
Better fuel economy
Combined with MacPherson struts: less unsprung weight for better handling
Transmission hump is eliminated
A few FWD engines have been mounted longitudinally
Most transaxles mounted sideways

8. Manual Transaxle Manual transaxles and transmissions
Use same kind of clutch
Three parallel paths for power flow
Input shaft located above intermediate shaft
Input shaft gears directly drive output shaft gears
Differential assembly
Gear shafts
Supported by larger ball, roller, or tapered roller bearings
End play is controlled by thrust washers

9. Shift Linkage Transverse transaxles Two shift cables or rods Advantage
Shifted by cables or shift linkage
Two shift cables or rods
One moves a selector on transaxle
Other moves shift fork back and forth
Advantage
Engine shake is not transmitted back to driver’s hand on shift lever

12. Transaxle Differential
Allows wheels to turn at different speeds when rounding corners
Same as rear-wheel-drive differential
Ordinary helical gearset
Used instead of bevel gears
Power from differential side gears is transmitted to front drive axles through axle shafts

13. Transaxle Power Flow Five-speed power flow
Fixed gears for first, second, and reverse on input shaft
Fixed gears for third, fourth, fifth on intermediate shaft
Power flow leaves transmission intermediate shaft
Continues through drive pinion to axles
Engine is mounted sideways
Axles run parallel to input shaft

16. Automatic Transaxle
Combination of automatic transmission and differential
Same parts and operation apply
Transverse engine
Power flow is through gears or sprocket and chain
Chain drive
Allows transaxle to be mounted slightly below and to the side of the engine

17. Front Drive Axles
Difference between rear-wheel drive and front-wheel drive axles
Front-wheel drive axles have CV joints at ends
Axles driven at sharper angles
Allow steering front wheels during power transmission
Universal joint changes output speed twice in every revolution when run at an angle
Rear-wheel drive vehicle drive shaft turns very fast
Positioned before gear reduction of differential

18. Axle Shaft Parts Drive axle is called half shaft or axle shaft
Stub shaft (stub axle)
Short shaft at outside end
Splined to front hub so it can drive front wheels
CV joint classifications
Inboard and outboard
Fixed and plunge
Ball and tripod

19. CV Joint Construction Most common joint combination Fixed joints
Rzeppa joint for outside fixed joint and a tripod for inside plunge joint
Fixed joints
Rzeppa joint: ball-and-socket type
Types of plunge joints
Tripod tulip
Double offset plunge joint
Cross groove plunge joint

22. Axle Shafts Characteristics May be solid or hollow
May have damper weights to absorb vibration
Turn much slower than rear-wheel drive shaft
Balance not as important
When different lengths: long one twists and lags before puts its torque to the wheel
Torque steer is prevented by longer axle shaft of larger diameter tubing

25. CV Joint Boots Boots at each end of axle contain grease CV joint boot
Protect joint from the elements
CV joint boot
Attached to axle and stub shafts with plastic or steel bands or straps
Made of natural rubber, neoprene, silicone, or urethane