1. Driveline Operation
Chapter 75

2. Objectives Describe the operation of universal joints
Explain how a differential works
Understand the differences between types of limited slip differentials
Describe the different types of rear axles and bearings
Select the correct gear oil for different applications

3. Objectives (cont’d.)
Identify differences between four-wheel-drive types
Explain the parts and operation of a transfer case

4. Introduction Driveline Live axles FWD vehicles
Parts that transfer power from transmission to rear wheels
Driveshaft and universal joints
Axles and axle bearings
Differential
Live axles
Turn with the wheels
FWD vehicles
Have a transaxle with two halfshafts

5. Drive Shaft (RWD)
Typically include two universal joints and slip yoke

6. Slip Yoke Attached to universal joint on front end of drive shaft
Other end fits over splines on output shaft
Slides in and out of transmission
As distance between transmission and differential changes
Automatic transmission
Sometimes a seal goes over the output shaft
Keeps ATF from leaking out of slip yoke through its vent hole

7. Universal Joints U-joints are located at ends of drive shaft
Axle moves up or down: U-joint allows changes in angle at ends of drive shaft
Cross and yoke
Most popular design
Usually pressed fit into the yokes on drive shaft
Snap rings fit into grooves in the yoke
Popular method of connecting to the differential
U-bolts hold U-joint centered between tabs in the rear flange

8. Two-Piece Driveshaft During factory balancing
Weights spot-welded to drive shaft
Vehicles with longer wheel base have a two-piece drive shaft
Correctly assembled driveshaft
U-joint cups in alignment
Improperly assembled: severely out of balance
Center support bearing
Holds center of shaft where two shafts attach
Sealed bearing is supported in rubber mount

9. Driveshaft Angle Cardan U-joint operated at an angle
Speed of driven shaft varies as it revolves
Angle is increased: change in velocity increases
Most manufacturers use angles less than three to four degrees with single U-joints
One-piece drive shaft
U-joints arranged so they cancel each other
Angles at each end of drive shaft
Must be almost equal or vibration results

10. Constant Velocity Joints
Vibration caused by drive shaft speed
Canceled by putting two Cardan U-joints next to each other
U-joints: connected by centering socket and yoke
Phased to cancel each other’s angle
Speed change never leaves the joint
CV joints: used on larger luxury vehicles and pickup trucks
Ball and trunnion: used on FWD vehicles

11. Differential and Differential Construction
Differential transfers power to wheels
Increases torque with final drive gear reduction
Differential construction
Parts are housed in axle housing
Pinion gear is splined to flange
Crush sleeve functions
Keeps bearing separate from races
Maintains preload on bearings
Keeps front bearing race from spinning

12. Differential Housing Differential housing holds drive pinion and case
Banjo housing has removable pumpkin
Salisbury axle (integral): third member not removable
Top of housing has vent and breather tube
Breather tube usually runs into fender well
Vent may have one-way check valve

13. Differential Operation
Each axle has splines
Mesh with side gear splines
Differential pinions mesh with side gears
Mounted on pinion shaft
Spider gears
Side gears and differential pinions
Power flow
During corner: side gears rotate against differential pinions

14. Differential Gears Hypoid gearset
Pinion gear: lower than the centerline of ring gear
Teeth of hypoid gear: curved in spiral shape
Each tooth has concave and convex side
Convex side is the drive side
Concave side is the coast side

16. Gearsets Ring and pinion gears: produced as matched set Gearset types
Ring and pinion gears marked
Assembled with marks facing each other
Must be mounted together in exact position
Gearset types
Hunting gearset: pinion gear tooth moves around until it contacts all of the ring gear teeth
Non-hunting gearset: one tooth on pinion gear meshes with same tooth on ring gear
Partial non-hunting gearset: one pinion tooth contacts two to three different ring gear teeth

17. Axle Ratio and Limited Slip Differential
Axel ratio: divide number of teeth on pinion gear into number of teeth on ring gear
Manual transmission has lower ratio
Higher ratio produces better fuel economy
Limited slip differential: locks up spider gears when one wheel loses traction
Puts traction on the still wheel
Spider gears not locked during normal operation

18. Types of Limited Slip Differentials
Several designs
Most popular has clutch packs
Torque applied to clutch pack: side gear locks
Older units: four pinion gears and two pinion shafts
Cone-type: cones forced against case by springs
Viscous coupling: sealed unit contains silicone fluid
Detroit Locker differential: has a ratcheting pair of clutch packs that force it to lock up

19. Drive Axles and Bearings and Semi-Floating Axel Bearing Types
Support weight of the car
Semi-floating axle bearings
Bearing retained axle: bearing with inner race pressed onto axle shaft
Retainer ring pressed onto axle shaft after bearing
Outside of bearing fits tightly into axle housing
C-lock axle: bearing rides on hardened axel areas
Outer bearing race and rollers fit into axle housing
Axle bearing lubricated by oil mist

20. Independent Rear Suspension Axles
Vehicle has independent rear suspension
Axles must pivot independently
Two swing axles
Each axle has universal joint at one or both ends
Similar to those used in front-wheel-drive cars

21. Gear Oils Special heavy liquid lubricant for gears and bearings
Prevents high temperatures and scoring of parts
Additives prevent corrosion and oxidation, reduce friction, limit wear, and prevent foaming
EP additives: cause formation of compounds
API system
Classifies gear lubricants
Limited slip gear oils
Require friction modifier additive

22. Four-Wheel Drive and Four-Wheel Drive Axle Assembly
Types of four-wheel-drives
Operates like RWD with extra differential in front
Operates like FWD with extra differential in rear
All-wheel-drive are always in four-wheel-drive
Axle assembly for four-wheel-drive: similar to two-wheel-drive rear axle
Drive shaft and universal joints transfer by way of transfer case
Ends of axle housing on front axles have to pivot to allow front wheels to be turned

23. Transfer Case
Allows for shifting between low and high range and two-wheel and four-wheel drive
Power flow using gear drive transfer case
2H: through locked planetary gearset to mainshaft and rear differential
4H: input shaft to locked planetary gearset
4L: shifter moves clutch rearward
Planetary low range
Planetary transfer case: ring gear pressed into housing so it is held stationary

24. Locking Hubs Allow four-wheel drive to be used in two-wheel drive
Types
Manual locking hubs: have on and off locks on front spindles
Unlocked: front wheels not driven
Automatic locking hubs: come on when vehicle shifted into four-wheel drive

25. All-Wheel Drive Characteristics All four wheels driven
Used to improve traction on icy or snowy driving
Transfer engine power to wheel with most traction
Lockout must be included when there is a center differential
Viscous coupling allows front and rear wheels to revolve at different speeds
Intelligent AWD flexibly distributes torque to wheels