CV Axles And Boots

The common complaint of an unfamiliar sound coming from under a vehicle in for repairs often leads you to discover a worn or failed rubber boot. Most suspension parts rely heavily on good lubrication, and good lubrication must be contained and protected by a rubber boot within its working cavity. Sometimes you only need a small boot with minimal amounts of grease – because the movement is small. However, in the case of a CV axle, large amounts of grease must be held in the cavity as the boot is subject to a wide array of movement and angles.


CV axles are a part of the drivetrain that transfers power from the engine to the wheels. They are most commonly found on a front-wheel drive vehicle, however CV axles can also be found on independent rear suspensions on rear wheel drive vehicles.


The axles receive rotational power (or torque) from the engine drive shaft and transfer it directly to the hub, thus the name Constant Velocity axle. Each CV axle drives a single wheel, so a pair is always required.


You will find in most vehicles that one CV axle side is shorter than the other, typically the driver’s side and a longer shaft on the passenger side. You should identify the longer shaft first as this typically is going to be the side that fails first. Since this shaft is longer, more force is applied to it and as a result, it tends to wear quicker. Once the weak side begins to wear, it directly affects the other side. It is recommended when a CV axle is worn, to always replace them in pairs so there is no imbalance to the vehicle’s suspension and ride control.


Because CV axles are the direct link between the engine and the wheels, they are subject to high levels of stress over time and will eventually wear out. When they do wear out, the CV axles usually will produce a few symptoms that can alert the driver that they require attention. There are two common areas on the CV axle that will be most affected by wear: the first is within the outer joint housing and the second is inner joint spline damage.


Listen for the pop

The most common symptoms associated with a failed CV axle are clicking or popping noise occurring when slowing down or when the steering wheel is at full lock while driving. Initially this noise could be quite subtle, but once detected, it should not be left for long because the CV axle is in constant use under large amounts of force and will fail quickly.


Sometimes you may need to differentiate whether it is a failed cv axle, or a loose or failed strut mount and the simplest way to figure this out is to drive over a speed bump, if you get the noise consistently, this is pointing to a failed strut mount. You can also lift the wheel off the ground and slightly rotate it backwards, then forwards – if the pop is heard a damaged CV axle is the most likely reason.


Check the Wheel Nuts

Always ensure that the wheel nuts have been installed correctly to the proper torque specs. Over tightened or under-tightened nuts will create additional forces that will translate into vibration and damage to the axle.


Look for Grease

When diagnosing a noise and you suspect the CV axle, look around the general area and look for grease spray on the inside of the tire or in the surrounding area. This could indicate a damaged boot. A CV axle assembly has two boots, one covering the tripod joint and the other covering the CV joint. Boot failure is the most common problem associated with CV axle failure.


Check Rubber Boots

A dry or damaged boot could cause grease to escape and could allow moisture and dust to enter. The grease is critical to proper function, therefore if it escapes, the lack of lubrication will lead to failure. If external objects or particles manage to enter the joint housing through boot damage, axle failure could also occur. Through a proper inspection, this type of damage can be identified and fixed before the axle fails completely.


Visually check surrounding parts

Look around in the suspension area for damage because of a foreign object strike, or even leaking fluids from other components in the engine and check the joints of other suspension components – often one failed part affects the integrity of other parts in the system.


Specific to Limited-slip differentials, excessive backlash because of gaps in worn gears and splines in the differential will damage the CV axle – check differential fluid for metal flakes or a burnt oil odor to make sure all is well.


When more serious damage is present, the shaft can become unbalanced and will start vibrating badly. This will be most evident during deceleration when the shaft is not loaded with torque, however in some cases, it might also show up when driving at highway speeds.


Special Circumstances: Extreme Duty conditions

There are additional indicators for those who drive in rugged conditions or extreme temperatures, either cold or hot, wet or dry. In these conditions regular CV axle grease may fail and boot rubber may get brittle. This is often because normal operating temperatures were exceeded. If the temperature is too extreme the lubrication of the bearing races begin to harden up. This can start to affect the function of the boot, will create stiffness in the joint, and will increase friction inside the joint housing.


It can also result in hard deposits and wear in the surface of the bearing race – this will gradually form a depression in the race surface causing the ball bearings to pop in and out when it running over the damage, particularly when the steering is at full lock.– this is the noise that you will most often hear.


Extreme temp situations call for extreme duty rated parts, specifically designed and engineered to withstand the elements and deliver the same performance you would expect under normal conditions. GSP specializes in CV Axle technologies and has developed a line of Xtreme Duty (XD) CV axles specifically to handle driving in those types of conditions.


CV axles serve as the final link between the engine and the wheels, when replacing them don’t sacrifice the quality of the parts you choose. They serve the important function of transferring the torque from the drivetrain to the vehicle's wheels in order to move the vehicle. It is important to take the proper steps in identifying any changes or unusual noises that may arise and address them promptly with high quality parts that keep you driving forward. Discover GSP CV Axles and XD Cv axles for more information on complete solutions.

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