Why Front Wheel Drive?

Front wheel drive is the most space and weight efficient way to package the elements of a passenger car. The drivetrain (engine, transmission, and differential) are all part of one compact unit. This has allowed for changes from leaf springs to coil springs in the rear, from shock absorbers/coil springs to McPhearson struts in the front and the elimination of the hump that runs down the middle of the car. The results are superior handling, better traction, improved gas mileage and more interior room.

Front wheel drive automobiles have been commonplace in Europe since the 1930's and even appeared on the U.S.-built Cord in 1929. However, it wasn't until 1966, with the introduction of the Oldsmobile Toranado and Cadillac Eldorado, that front wheel drive cars caught the attention of American car buyers. Today, over 65% of all the cars on the road and over 90% of all new cars sold in die U.S. are front wheel drive.

How Does It Work?

There are two drive axles - also known as half shafts - on a front wheel drive vehicle. Each shaft carries power from the differential gear box to one of the wheels.

Because the wheels move up and down independently, a flexible joint is needed at both ends of each shaft. These joints enable power to flow to the driving wheels while allowing the wheels to steer. At the same time, the drive axles must move along with normal suspension movement including angles as steep as 45O. These joints are called constant velocity joints (CV joints) and every front wheel drive vehicle has two drive axles and four CV joints (2 inboard and 2 outboard). CV joints contain precision bearings and must be protected from road hazards and the elements. Protection is provided by a flexible rubber boot that resembles a bellows.

The Boot

Because it is exposed, the boot can be torn or cracked. When this happens, grease protecting the CV joint can leak out or contaminants can get in. It is important that your technician immediately replace a damaged boot. Failing to do so will lead to extensive damage of the CV joint and premature costly replacement. Properly maintained, a front wheel drive assembly has a normal replacement life of 80,000 to 100,000 miles.

The CV Joint

A worn or damaged CV joint will make its presence known by clunking, clicking or vibrating. If any of these occur, have the front drive assembly checked immediately. It is dangerous to drive a vehicle that needs a CV joint replaced. A damaged CV joint cannot correct itself and if it is loud enough to hear, it is beyond repair.

The Drive Axle

Axles are made of hardened steel and are extremely durable, but they can be damaged by road hazards like rocks or potholes. If this happens, replacement is necessary for the vehicle to handle properly. A damaged axle can be detected by vibration of the vehicle or checking the axle for cracks.

What To Do

When a CV joint or front drive axle needs replacing, we recommend replacing the entire drive assembly as a single unit instead of merely replacing one end. Often times, when a joint or boot is damaged, the other is on its way to failure. Complete replacement guarantees a proper repair and is about the same cost as rebuilding and replacing a single joint or axle.

It might seem logical to replace both drive assemblies at the same time, but both sides may not wear at the same rate. If a boot is torn from road debris, this will cause premature wear and failure to that side only. Under normal wear conditions, both sides should be replaced since wear is relatively even, right to left. The best way to determine the side that has failed is a complete diagnosis of the problem by your local technician.

Other Vehicles

Just because your vehicle is not front wheel drive doesn't mean it is not equipped with CV joins. Rear wheel drive cars with independent rear suspension, cars equipped with all-wheel drive and many four-wheel drive vehicles use CV joints. Be aware that these vehicles are subject to the same conditions as front wheel drive vehicles.