Driveshaft – Lesson 4 | Manual Transmission and Drivetrain

Driveshaft – Lesson 4 | Manual Transmission and Drivetrain


Manual Transmission and Drivetrain : Lesson 4 – Driveshaft



Upon completion of this lesson, you will be able to:

! Explain the purpose and function of a driveshaft.

! Describe a driveshaft and identify the types.

! Identify the components of a driveshaft.

Explain the theory and operation of a driveshaft.


At a glance


order for a rear axle to be driven, a rear-wheel-drive vehicle needs a driveshaft. The driveshaft transfers the rotation torque of the transmission output shaft to the differential, causing the rear wheels to turn.

Front-wheel drive vehicles and vehicles with independent front or rear suspension require unique driveshafts called half shafts.



Typical rear-wheel-drive driveshaft

  1. Driveshaft
  2. Transmission tail shaft
  3. Universal joints (U-joints)
  4. Rear-axle assembly


At a glance

Drivetrain angles



Drivetrain side view and top view

  • Acceleration
  • Deceleration


As a vehicle is driven, the angle of the drivetrain constantly changes due to the movement of the axle assembly. As the vehicle load changes or the wheels hit bumps or holes in the road, the axle moves up and down in relation to the frame. When driving or braking torque is applied, the rear axle may also wind up or down on the suspension.

The transmission, however, is fixed to the frame. Without flexibility, the driveshaft would bend and eventually break. U-joints and slip yokes provide the drivetrain with the flexibility needed. The driveshaft can smoothly transfer torque while rotating, changing length, and moving up and down.



At a glance

Split driveshafts



Split driveshaft components

  • Driveshaft
  • Center bearing
  • Driveshaft
  • Slip yoke
  • U-joint



Driveshaft components

Universal joints



Single Cardan U-joints

  • End yoke
  • Grease seal
  • Needle rollers
  • Bearing cup
  • Thrust washer
  • Slip yoke
  • Cross shaft (spider)
  • Snap rings
  • Driveshaft

Single Cardan U-joints (named after the designer) consist of a center cross shaft assembly and two yokes. Each yoke can rotate around the axis made by mating ends of the cross shaft. Snap rings to secure the bearing cup to the yoke and may be internal or external. Original U-joints are lube-for-life. Some U-joints are equipped with a nylon thrust washer at the base of the bearing cup.



Driveshaft components (continued)



Double Cardan U-joint

  • Cross shaft assembly
  • Center yoke
  • Cross shaft assembly
  • Slip yoke
  • Centering spring
  • Socket yoke
  • Companion flange


Double Cardan U-joints are used when the operating angle is too large for a single joint to handle. The double Cardan U-joint consists of two individual Cardan U-joints closely connected by a center yoke and a socket yoke. The center yoke, socket yoke, and centering spring keep both U-joints in line with each other. This assembly splits the angle of the two shafts between the two joints.



Driveshaft center bearing




Typical center bearing

  • Driveshaft and coupling shaft
  • Dust slinger
  • Rubber insulator
  • Driveshaft center bearing bracket
  • Bearing shield (retainer)
  • Center bearing
  • Splined stub shaft end
  • Blind spline

The two-piece driveshaft used in some vehicles consists of two shafts, three U-joints, and rubber insulated, frame-mounted center bearing. The center bearing is needed to support the two-piece driveshaft assembly during operation and is pre-lubricated and sealed for life. The front U-joint is positioned almost straight so that it does not generate a speed fluctuation, and the other two joints are phased to prevent vibration.



Driveshaft components (continued) Flex couplings




Typical flex coupling driveshaft assembly

  • Flex coupling
  • Center bearing retaining ring
  • Center bearing
  • Slip yoke
  • U-joint
  • Pilot bearing
  • Balance nut
  • Center locknut
  • Driveshaft

Some vehicles use flex couplings in place of the U-joints. Flex couplings are made of rubber. Flex coupling operating angles must be within one degree.



Driveshaft operation

Operating angles and balance



Drivetrain operating angles

  • Transmission to driveshaft angle
  • Driveshaft to axle angle
  • Axle 4 Transmission

U-joints, accommodate the changes in the operating angles at each end of the driveshaft. The slip yoke accommodates driveshaft motion by adjusting the length of the shaft. To operate properly, driveshafts must be balanced and sized. The range of the operating angles must also be matched. In a one-piece driveshaft system, there are two driveshaft operating angles. The first is the angle between the transmission, or transfer case output shaft and the driveshaft. The second is the angle between the driveshaft and the rear axle input shaft.



Driveshaft operation (continued)

Driveshaft phase



Each shaft must be assembled with yokes in the same plane

The U-joints on each end of the driveshaft must also be in phase. Being in phase means that the driven yoke must have the same point of rotation, or the same plane, as the driving yoke. Phasing will allow each shaft to speed up and slow down at the same time during each rotation, which will minimize any vibrations during normal operations. If the shafts are not in phase, the slowing down and speeding up of the driveshaft will be transmitted to the axle even if the operating angles are parallel, resulting in damaging vibrations.


Halfshaft overview

Half shafts

Front-wheel drive vehicles require unique drive axles called half shafts. The half shafts transfer power from the differential in the transaxle to the wheels.

Half shafts are connected between the side gears of the differential and the wheel hub. Half shafts must be able to smoothly transmit torque during turns and to change length as the vehicle travels over bumps, or as vehicle load changes.



Typical halfshaft assembly

  • Left halfshaft assembly
  • Right halfshaft assembly


Halfshaft overview

Halfshafts (continued)

Varying halfshaft length

The half shaft provides this smooth transfer of power because of the constant velocity (CV) joints located at each end of the shaft. CV joints are designed to allow a smooth transfer of torque while allowing for steering and front suspension movement.

As the suspension moves, the CV joints allow the half shafts to change the length and operate smoothly through varying angles. The outer CV joints allow the steering system to turn the wheels, as well as allow for the up and down movement of the suspension. The inner CV joint allows for halfshaft length change (plunge) due to suspension movement.



Halfshaft length change

  • Halfshaft extended
  • Halfshaft compressed


Halfshaft operation

Halfshaft operation

During vehicle operation the outer CV joint pivots, allowing the shaft to change angles quickly and smoothly. Power is transferred even when the vehicle is being turned sharply. At the same time the inner joint also allows pivoting, but it also can change length. Pivoting and length change is done because the components of the inner joint ride in a sleeve and can move in and out along its length as needed when the suspension is reacting to the contours of the road. This ability is called “plunge”.



Halfshaft assembly

  • Inner CV joint
  • Outer CV joint is fixed


Halfshaft components

Basic halfshaft components

Inner CV joint

Common components found on all halfshafts include:

! CV joint boots

! Inner CV joint

! Shaft

! Outer CV joint



The inner CV joint is splined to the side gear of the differential. To prevent the inner CV joint from easily pulling out of the side gear, it is held in place using a spring steel circlip. There are two common types of inner CV joints.

The tripod-type joint shown above has three trunnions fitted with special rollers that ride on needle bearings.

! Tripod joint rides inside the sleeved race of the joint housing (sometimes called the tulip because of its appearance).

! Since the rollers are not fixed to the joint housing, they are free to move back and forth inside the joint housing.

! The movement of the rollers allows for angulation of the shaft as well as letting it change length for suspension action.


Halfshaft components

The plunging ball-type inner CV joint uses an outer race that has straight grooves machined into it.

! The inner race is connected to the shaft, and large caged ball bearings ride between the inner and outer races.

! As the shaft changes length, the inner race and caged ball bearings are free to move in and out along the grooves of the outer race, thus letting the shaft angulate and change length.



Plunging ball joint

  • Circlip
  • Housing/outer race
  • Snap ring
  • Inner race
  • Bearing cage
  • Ball bearings
  • Bearing retainer
  • Boot clamp
  • CV joint boot
  • Boot clamps


Halfshaft components

Basic halfshaft components (continued)


The shaft of the halfshaft assembly is splined at both ends to allow the CV joints to be fitted to it.

! Since the shaft rotates at only about 1/3 the speed of a rear wheel drive driveshaft, it does not need to be balanced.

! Some shafts use rubber dynamic dampeners to help eliminate small vibrations that may be generated during vehicle operation.



Intermediate shaft

Vehicles with larger engines may require the use of an intermediate shaft. An intermediate shaft is a shaft that connects from the transaxle to the halfshaft assembly and is supported by a hanger bearing that is bolted to the vehicle frame.

The intermediate shaft is needed on some vehicles because the farther from the center of the vehicle that the halfshafts are connected to the transaxle, the more torque steer is felt at the steering wheel. Torque steer can be very pronounced on vehicles with large engines whose transaxles are not located at the vehicle centerline.

Halfshaft components

Outer CV joint

The outer CV joints used on many vehicles are Rzeppa-type joints (named for their inventor). These joints are fixed ball joints that consist of an inner ball race, a set of large ball bearings that are caged into position. These ball bearings move inside of races machined into the outer housing. When the wheels are turned for vehicle steering, the ball bearings allow the inner race, which is splined to the shaft, and the outer race, which is splined to the wheel, to operate at angles to each other.

The outer race of the CV joint is splined to the wheel hub using an interference fit. This interference fit eliminates backlash between the wheel hub and the halfshaft. However, because of the extremely tight fit of interference fit splines, a special service tool must be used when removing the CV joint from the wheel hub. Vehicles with anti-lock brake systems (ABS) will have the wheel speed sensor ring of the ABS around the outside of the outer CV joint housing.

CV joint boots

Both inner and outer CV joints have rubber or plastic boots that cover the opening of the joint where it connects to the shaft. These boots are held in place by special clamps. The boots are designed to keep contamination out of the CV joint, and to keep the special grease used to lubricate the joints from escaping. Any tear in the boot, or damage to the boot clamp that allows contamination into the joint requires either boot or joint replacement.



Rzeppa-type CV joint

  • Boot clamp
  • CV joint boot
  • Boot clamp
  • Ball bearings
  • Outer housing


Read More…

Drivetrain – Lesson 1 | Manual Transmission and Drivetrain

Clutch – Lesson 2 | Manual Transmission and Drivetrain

Transmission / Transaxle – Lesson 3 | Manual Transmission and Drivetrain

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