Audi Coupe Quattro Front Axle Replacement Cost
How Much Does an Axle/Half Shaft Replacement - Front Cost?
Axle/Half Shaft Replacement - Front Service and Cost
Front drive axles are responsible for transmitting power from the transmission or differential to the wheel hub. There are two types, straight axles and constant velocity (CV) axles.
Front drive axles are built from high strength metal to withstand transmitting power from the engine to the wheels, and carrying the load of the vehicle. They have geared ends called “splines” that stay in constant mesh with the differential and the hub and bearing assembly. Straight axle type drive axles spin inside of a tube called the axle housing, which contains the differential in the center, both right and left axles, and wheel bearings. Unlike a straight rear axle, the front axle must bend to allow the wheel to turn. This bending is accomplished using a universal joint. Independent suspension vehicles use constant velocity (CV) axles, that have articulating heads at both ends, allowing the wheel to move independent of the differential in all directions. The CV gears at the ends are enclosed in a thick rubber material, called the “CV boot”, that prevents grease from escaping, and dust from entering. CV axles have become far more common to see in modern passenger vehicles, while straight axles remain dominant in heavy duty applications.
When a straight axle fails, it may cause vibration while driving, as the axle may have become warped or twisted, or the universal joint is worn. If the wheel bearing has failed, the axle and bearing will make a grinding noise while driving. This may also be accompanied by vibrations in the steering wheel and brake pedal. .
Driving with a faulty axle or wheel bearing is dangerous. Aside from the vehicle feeling unstable, the wheel may come off when the bearing completely disintegrates. If mechanical grinding is heard from the wheel bearing, the vehicle should be taken out of service to prevent further damage and unsafe driving conditions.
Straight axles tend to fail less than CV axles because of their heavy-duty nature. The typical front CV axle should last between 80,000 – 100,000 miles, but driving style can significantly increase or decrease service life.
Axle/Half Shaft Replacement - Front Repair Information
Diagnosing a failed axle will being with a visual inspection and test drive. If symptoms point to a faulty front axle, the axle will be inspected for damage, and if the technician heard audible clicking from the CV joints while driving, the CV axles will be replaced. If the visual inspection revealed torn CV boots, but no damage is evident to the CV gears, the CV boot may be replaced. For straight axles, the wheels may be turned by hand to verify the issue prior to removing the axle for inspection. Removing the axle requires the differential cover to be removed, and axles disconnected from the differential. Then, the brake drum, or caliper and rotor, hub, and axle must be removed. The bearing and axle will be examined, and if damage is present where the axle meets the bearing, they must both be replaced. Lastly, a warped straight axle will be diagnosed with a straight edge, and by wear patterns from the wheel bearings and differential.
The replacement procedures for the two axle types are dissimilar, and will be separated here. For CV axles, the wheel, axle nut or axle bolt, brake caliper, brake caliper mounting bracket, and brake rotor must be removed. Then, the most advantageous suspension component is disconnected from the steering knuckle to allow the CV axle to slide free from the bearing and hub assembly. The CV axle is then removed from the transmission or differential, and the new shaft will be installed in the reverse order. Note, it should not be necessary to bleed the brakes for this service, even though they are removed. For straight axles, removal of all the same components is necessary, with the addition of the differential cover. This cover must be removed to disconnect the drive axle from the differential. The differential will be cleaned, inspected, and resealed when the new axles are installed.
We recommend following the manufacturer's scheduled maintenance to help prolong the service life of the vehicle and individual components. Changing differential oil for straight axles is the single most important maintenance task, and the most often overlooked.
For both types of front axle, the amount of free-play in the wheel can be an indicator of a failed wheel bearing, which may cause damage to the axle if the vehicle is driven.
Only the most skilled DIYer should attempt to repair either type of axle. The novice or inexperienced will find many issues along the way that will prevent the vehicle from returning to an operational status. Also, these tasks take place under a raised vehicle, and unsafe lifting procedures cause injury and death. If driveline components and assemblies are thoroughly understood, this task will be labor intensive, and require specialty tools. Otherwise, this job should be given to a professional.