68 Chapter Drive Shaft and Transfer Case Technology

Objectives After studying this chapter, you will be able to: Identify and describe the parts of a modern drive shaft assembly. Explain the functions of a drive shaft. Describe the different types of universal joints. List the different types of drivelines. Explain the basic operation of a transfer case. Correctly answer ASE certification test questions that require a knowledge of drive shafts and transfer cases.

Drive Shaft Assembly Drive shaft assembly components Slip yoke Connects transmission output shaft to front universal joint Drive shaft Hollow metal tube that transfers turning power from front universal joint to rear universal joint

Drive Shaft Assembly (Cont.) Rear universal joint Flex joint connecting drive shaft to rear yoke Rear yoke Holds rear universal joint and transfers torque to gears in rear axle assembly and differential

Drive Shaft Assembly (Cont.) (Mazda)

Functions of Drive Shaft Assembly Sends turning power from transmission to rear axle assembly Flexes and allows vertical movement of rear axle assembly Provides sliding action to adjust for changes in driveline length Provides smooth power transfer

Drive Shaft Operation Transmission output shaft turns slip yoke Slip yoke then turns front universal joint, drive shaft, rear universal joint, and rear yoke on differential Differential contains gears that transfer power to rear drive axles Axles rotate wheels

Driveline Flex When tires strike a bump in the road, rear suspension moves upward and springs are compressed Universal joints Let driveline flex as rear axle moves up and down Protects drive shaft from any damage caused by movement

Slip Yoke Slip yoke, or slip joint Splined to transmission output shaft Allows for changes in driveline length by sliding in and out of transmission (Ford)

Slip Yoke (Cont.) Extension housing bushing Transmission rear seal Supports slip yoke as it spins in transmission Transmission rear seal Rides on slip yoke and prevents fluid leakage from rear of transmission

Rear Yoke Rear yoke is yoke bolted to outer end of pinion gear on rear axle assembly It transfers torque to gears in rear axle assembly Rear universal joint held by this yoke

Drive Shaft Drive shaft or propeller shaft Hollow steel tube with permanent yokes welded on each end Very strong and light Spins much faster than wheels and tires It must be straight and perfectly balanced

Drive Shaft Assembly (Toyota)

Drive Shaft Balance Drive shaft must be perfectly balanced, with its weight evenly distributed around its centerline Drive shaft balancing weights Welded to shaft to reduce vibration Drive shaft vibration damper Large, ring shaped weight mounted on rubber Helps keep shaft spinning smoothly by absorbing torsional vibration

Universal Joints Universal joint or U-joint Swivel connection capable of transferring turning force between shafts at angle to one another Simple universal joint made of two Y-shaped yokes (knuckles) connected by cross (spider)

Cross-and-Roller Universal Joint Cross-and-roller joint or cardan universal joint Most common type of drive shaft universal joint Bearing caps are held stationary in drive shaft yokes Roller bearings fit between caps and cross to reduce friction Cross is free to rotate inside caps and yokes

Cross-and-Roller Universal Joint (Cont.) (Chrysler)

Constant Velocity Universal Joint Constant velocity universal joint or double-cardan joint Two cross-and-roller joints connected by centering socket and center yoke Two joints operate together on one end of drive shaft Output shaft speed fluctuations are counteracted

Constant Velocity Universal Joint (Cont.) (Ford)

Ball-and-Trunnion Universal Joint Ball-and-trunnion joint Another joint designed for constant velocity Eliminates shaft speed fluctuations Allows for slight length changes in driveline Ball-and-trunnion joint seldom used

Center Support Bearing Holds middle of two-piece drive shaft Center bearing bolts to vehicle’s frame or underbody Supports center of drive shaft where two shafts come together

Center Support Bearing (Cont.) (Fiat)

Driveline Types Hotchkiss driveline Torque tube driveline Exposed drive shaft that operates rear axle assembly mounted on springs Usually has cross-and-roller universal joints Torque tube driveline Solid steel drive shaft enclosed in large hollow tube With independent rear suspension, drive shaft can be one piece without universal joint

Hotchkiss Driveline (Ford)

Transfer Cases Transfer case Sends power to both front and rear axle assemblies in four-wheel-drive vehicle Mounts behind and is driven by transmission Two drive shafts normally run from transfer case, one to each drive axle

Transfer Cases (Cont.) (Ford)

Two-Wheel-Drive, High Range (2H) 2H range provided for normal driving when four-wheel-drive traction not needed Sliding clutch remains in neutral position Torque is not transferred to front axle assembly

Four-Wheel-Drive, High Range (4H) Sliding clutch is shifted into main shaft clutch gear Torque then flows through drive chain, front output yoke, and front drive axle assembly Both front and rear axles drive vehicle

Four-Wheel-Drive, Low Range (4L) Torque transfer is almost same as in 4H Ring gear is shifted forward into lock plate This holds ring gear stationary Planet gears walk inside ring gear, producing gear reduction

All-Wheel Drive All-wheel drive Four-wheel-drive system that does not use conventional transfer case Designed for front-wheel-drive transaxle or transmission Transmission or transaxle in all-wheel-drive system is modified to allow power flow to front and rear drive axles

Drive Systems