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© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Objectives (cont’d.)• Identify differences between four-wheel-drive
types• Explain the parts and operation of a transfer case
© 2012 Delmar, Cengage Learning
Introduction• Driveline
– 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
© 2012 Delmar, Cengage Learning
Drive Shaft (RWD)• Typically include two universal joints and slip yoke
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Gearsets• Ring and pinion gears: produced as matched set
– 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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Drive Axles and Bearings and Semi-Floating Axel Bearing Types
• Drive axles – 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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
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