Axles and drive shafts

In this page we will cover two very important parts involved in transferring the power from the transmission / transaxle to the wheels: The axles and drive shafts.

As you know, the transmission and transaxle are attached to the engine and to the frame of the vehicle and they offer very minimum flexibility, the drive shaft must be able to flex as the rear axle or the front wheels moves or it will break. To allow the drive shaft to move without breaking they are equipped with either universal joints or CV joints depending on the application.

1- universal joints ( u-joints ): Most rear-wheel-drive vehicles use the cross and roller universal joint that consists of a center cross and two yokes welded to the ends of the drive shaft, this design allows torque to be transmitted from the transmission to the axle/differential assembly even when the rear wheels and axle are moving up and down over bumps.

The cross and yokes ride on needle bearing rollers by way of a machined cap that fits into the yoke. The cap containing the rollers is usually held in the yoke by snap rings, u-bolt or a bolted plate.

The cross ends are often called trunnions, since the needle bearings ride on the trunnions, the trunnions are smoothly machined, a hole in each trunnion leads to the center of the cross where a grease fitting is normally installed, it is through this grease fitting that grease is applied to the needle bearings inside the caps.

2- Constant Velocity Joints ( CV joints ): These type of joint is the best design to produce an even transfer of engine torque to the drive wheels, they are very smooth and are often used on front wheel drive vehicles, vehicles with independent rear suspension, and modern four wheel drive vehicles equipped with full independent suspensions.

There are two configurations used in modern CV joints:
  1- Tripod CV joint: This type of joint is normally used as the inner joint on a drive axle, it is a 3 trunnion system that transmits torque through various changing angles, it does it by allowing the trunnions to slide in their corresponding channels as they transmit torque.

 2- Rzeppa joint: this joint is normally used as the outer CV joint on a drive axle, it uses a series of ball bearings and a slotted cross assembly that holds the ball bearings in slotted channels and allows them to rotate in any direction. It can transmit power through a range of angles by allowing the ball bearings to move up and down on the cross as the drive shaft transmits torque through various angles.

On most front wheel drive systems the CV joint is designed in a way that it can compensate for changes in drive shaft lenght as the suspension travels up and down. Since both the tripod and Rzeppa joints change angles by the use of balls or trunnions that slide through channels, the balls or trunnions can also roll or slide in these channels to allow the CV joint to change its lenght.

Click on image to learn how to replace the left drive axle on a 1989 Toyota Camry

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 Click on image to learn how to replace the outer CV boot on a Honda Accord

  Click on image to learn how to replace the CV drive axles on a 2002 Hyundai Accent GS