Joseph Fink
Transmissions
Chapter 5 Front Drive Axles

Chapter 5 discusses the purpose of a FWD car’s drive axles and joints. It helps you to understand and describe the different methods used by manufacturers to offset torque steer. It also describes and names different types of CV joints currently being used, and the different designs of CV joints. It explains how a ball-type CV joint functions and how a tripod-type CV joint functions. Between 1975 and 1979 only 4-5 percent of the total vehicle population had front wheel drive. Today, RWD and all-wheel drive accounts for over 80 percent of the vehicle population. In all FWD and some 4WD/AWD systems, the transaxle is bolted to the engine and the axles pivot on CV joints. The outer parts of the axles are supported by the steering knuckles that house the axle bearings. Steering knuckles serve as suspension components and as the attachment points for the steering gear, brakes and other suspension parts. A CV joint is a constant-velocity joint used to transfer a uniform torque and a constant speed while operating through a wide range of angles. FWD drive axles are also called axle shafts, dive shafts, and half shafts. The axle shaft is connected to the differential by the inboard CV joint. The axle shaft then extends to the outer CV joint. A short spindle shaft runs from the outer CV joint to mate with the wheel assembly. The hub and wheel bearing assembly connects to the spindle shaft of the outer CV joint. The complete drive axle, including the inner and outer CV joints, is typically called a half shaft. The drive shafts, on a FWD vehicle operate at angles as high as 40 degrees for turning and 20 degrees for suspension travel. Each shaft has two CV joints, and inboard joint that connects to the differential, and an outboard joint that connects to the splines to a hub mounted with the wheel bearing in the steering knuckle. As a front wheel is turned during steering, the outboard CV joint moves with it around a fixed center. Up and down movements of the suspension system force the inboard joint to slide in and out. The drive axles from a transaxle extend from the sides out to the drive wheels. With the engine mounted transversely, the transaxle sits to one side of the engine compartment, typically to the left, or driver’s side. This means the position of the differential gears it also off center which requires that one of the drive axles must be longer that nth other. Unequal length drive axles, however, have been found to deliver more torque to the wheel with the shorter shaft. However, when the vehicle is accelerated, the wheel with the shorter shaft has more torque, causing that wheel to pull harder than the other wheel. The stronger wheel tends to pull ahead of the other wheel, which creates the induced steering pull toward the opposite side. This pull is called the torque steer. The spindle shaft commonly called the stub axle. Torques steer is a term used to describe a condition in which the car tends to steer or pull in one direction as engine power is applied to the driver wheels. The inner piece of the axle shaft is normally called the intermediate driver shaft, which severs to equalize the lengths of the two outer drive shafts. New design front struts created for better handling and reduced torque steer may not be so new after all. Toyota developed what has been called a “super strut” for some of its high performance models in the early 1990’s that incorporates many of the design features now found on Ford and GM units. Universal joins are commonly referred to as U-joints. Bellow-type bolts are rubber or neoprene protective covers with accordion-like pleats used to contain lubricants and exclude contaminating dirt or water. If the CV joint boot keeps the joint properly sealed, the joint can last more than