The drive shaft connects the transmission output shaft to the rear axle assembly. It consists of a slip yoke, universal joints, and drive shaft. The universal joints allow the drive shaft to flex and transfer power smoothly as the rear axle moves up and down. The drive shaft must be balanced to reduce vibration during high speeds. A transfer case splits power between front and rear axles for four-wheel drive vehicles. It has different ranges like 2H, 4H, and 4L to provide different gear ratios for various terrain.

1. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

2. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
Connects the transmission output shaft with the rear
axle assembly

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Components
 Slip yoke
 Front universal joint
 Drive shaft
 Rear universal joint
 Rear yoke

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

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Operation
 The transmission output shaft turns the slip yoke
 The slip yoke turns the front universal joint,
driveshaft, rear universal joint, and rear yoke on the
differential

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Driveline Flex
Universal joints let the driveline flex as the rear axle
moves up and down

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Slip Yoke
 Splined to the transmission output shaft
 Allows for changes in driveline length by sliding in
and out of the transmission
 The outer diameter is machined smooth, providing
a bearing surface for the bushing and oil seal in the
transmission

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Slip Yoke

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Drive Shaft
 Hollow steel tube with permanent yokes welded on
each end
 Very strong and light
 Lightweight units may be made of thin-wall
aluminum with longitudinally aligned graphite
fibers for added strength
 May be single-piece, or two-piece

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Drive Shaft
Typical drive shaft assembly

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Drive Shaft Balance
 In high gears, the drive shaft turns at the same
speed as the engine
 The shaft must be accurately balanced
 The shaft is rotated on a balancing machine at the
factory
 Steel balancing weights are welded to the shaft to
reduce vibration

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Drive Shaft Balancing Weights

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Vibration Damper
 The drive shaft may be equipped with a large, ring-
shaped weight mounted on rubber
 Helps keep the shaft turning smoothly by
absorbing torsional vibration

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Universal Joint
 Swivel connection capable of transferring a turning
force between shafts at an angle to one another
 Made of two Y-shaped yokes, connected by a cross
 Bearings on each end of the cross allow the yokes to
swing into various angles while turning

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Universal Joint

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Types of Universal Joints

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Cross-and-Roller

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Cross-and-Roller
 Cardan universal joint
 Most common type of joint
 The bearing caps are held stationary in the drive
shaft yoke
 The roller bearings reduce friction
 The cross is free to rotate inside the caps and yokes

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Bearing Cap Retention
Several methods are used to retain the bearing cap in
the yoke

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Cross-and-Roller Drive Shaft
Assembly

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Constant Velocity Joint
 A cross-and-roller joint tends to accelerate and
decelerate during each revolution, setting up
torsional vibrations
 A constant velocity joint has two cross-and-roller
joints connected by a centering socket and center
yoke
 By using two joints, the output shaft speed
fluctuations are counteracted

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Constant Velocity Joint
Speed changes at the output of the first joint are
offset by speed changes
at the other joint

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Constant Velocity Drive Shaft

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Ball-and-Trunnion Joint
 Constant velocity design
 Eliminates shaft speed fluctuations
 Allows for slight length changes in the driveline

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Center Support Bearing
 Holds the middle of a two-piece drive shaft
 Bolts to the vehicle’s frame or body
 Common on pickup trucks and large vehicles with
long wheel bases
 The rubber mount prevents noise and vibration
from transferring into the passenger compartment

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Center Support Bearing

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Center Support Bearing

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Two main types—Hotchkiss
driveline and torque
tube driveline

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Hotchkiss Driveline
 An exposed drive shaft operates a rear axle
assembly mounted on springs
 Most common type of driveline
 Universal joints are used at both ends of the drive
shaft
 Cross-and-roller universal joints are most
commonly used

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Torque Tube Driveline
 Uses a solid steel drive shaft enclosed in a large
hollow tube
 Only one swivel joint is used at the front
 The rear of the torque tube is a rigid part of the rear
axle housing

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 Used to send power to both the front and rear axle
assemblies in a four-wheel-drive vehicle
 Mounted behind, and driven by, the transmission
 Two drive shafts run from the transfer case, one to each
drive axle

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Transfer Case

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Four-Wheel Drive versus All-Wheel
Drive
 Four-wheel drive has a transfer case separate from
the transmission
 drive ranges such as 2H, 4H, and 4L are provided
 All-wheel drive has the transfer case included as
part of the transaxle

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Four-Wheel Drive versus All-Wheel
Drive

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Transfer Case Construction
 Constructed much like a manual transmission
 uses shift forks, splines, gears, shims, and bearings
 Made of cast iron or aluminum
 Filled with lubricant (oil) that cuts friction

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Transfer Case Construction

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Transfer Case Ranges
 Two-wheel drive, high range (2H)
 normally provides a gear ratio of 1:1
 Four-wheel drive, high range (4H)
 normally provides a gear ratio of 1:1
 Four-wheel drive, low range (4L)
 normally provides a gear ratio of approximately 2:1

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Power Flow

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Two-Wheel Drive
(High Range)
 Provided for normal driving when four-wheel drive
is not needed
 Torque flows from the input gear to the locked
planet gears and ring gear, which rotate as a single
unit
 Torque is transferred to the main shaft through the
planet carrier
 Power flows out the rear yoke

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Four-Wheel Drive
(High Range)
 Torque flows through the input gear, the planet
gears, and ring gear as in 2H
 The sliding clutch is shifted into the main clutch
gear
 Torque flows through the drive chain, to the front
output yoke, to drive the front axle assembly
 Both axles drive the vehicle

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Four-Wheel Drive
(Low Range)
 Torque transfer is almost the same as in 4H
 The ring gear is shifted forward into the lock plate,
holding the ring gear stationary
 The planet gears walk inside the ring gear,
producing a gear reduction

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All-Wheel Drive
 Does not use a conventional transfer case
 Designed for a front-wheel-drive transaxle or a
transmission
 The transmission or transaxle is modified to allow
power flow to the front and rear drive axles

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All-Wheel Drive
A fluid coupling controls the power split to the front
and rear axle assemblies