Many times you do not know that your constant velocity (CV) boots have failed until it is too late. You’ll know it is too late when you are now getting the infamous clicking noise while you are driving and turning your steering wheel. That clicking noise indicates that the joint on the axle has failed and that the axle shaft needs to be replaced as an assembly. Knowing some of the signs of a bad constant velocity boot can help you to identify when the boot has failed, which can allow you to replace it or have it replaced before the axle joint fails.
Part 1 of 3: What is the purpose of a constant velocity (CV) boot
The constant velocity, or CV, boot is a cover that goes over each of the joints located on a constant velocity axle. The constant velocity axle is typically used on front wheel drive vehicles, but can also be used on the rear of all wheel drive and rear wheel drive vehicles. The axle itself is used to transfer power from the transmission or differential to the drive wheels.
The axle has a joint on each end that allows the axle to flex and move with the suspension and steering components. It is called a constant velocity joint because the design allows the joint to flex through the use of bearings while maintaining a constant speed.
The purpose of the boot itself is to cover the joint. The boot is used to hold a special grease within the joint itself to keep it lubricated. It also keeps dirt and other contaminates from entering the joint. If the boot fails, then the grease will be allowed to leave the joint causing it to run dry which will ultimately lead to the failure of the bearings inside of the constant velocity joint. Should this occur, the axle assembly would need to be replaced.
Part 2 of 3: Do an initial inspection
Prior to lifting the vehicle off of the ground, there are a couple of inspections that can be done to try and diagnose a failing constant velocity boot.
Step 1: Check for grease on your wheel. When looking at your wheels, if there is any grease on them, then that is an indication that there is a CV boot failure.
When the outer boot fails, the grease to come out of the joint and while the axle is spinning the grease will typically get thrown on the wheel.
Step 2: Check for grease on your fender well. Due to the design of some cars, the CV joint grease cannot make its way onto the wheel itself.
Many times it is thrown onto the fender well liner. Inspect the fender wells for signs of grease which would indicate a possible failing CV boot.
Part 3 of 3: Do an under vehicle inspection
Your initial inspection may or may not reveal any signs of a bad constant velocity boot. If nothing is found, then further inspection of the boots needs to be done. At that point, you will need to inspect them from under the vehicle.
Step 1: Park your car. Park your vehicle on a flat, hard surface and apply the parking brake.
Step 2: Chock the tires. Place the wheel chocks around the rear tires.
Step 3: Jack up the car. Working on one side at a time, place the floor jack under the front jacking points and lift the vehicle high enough to where you can easily get underneath it.
Step 4: Lower vehicle onto jack stand. Place the jack stand under the jacking point on your vehicle and lower the vehicle onto the jack stand.
With the vehicle in the air you will be able to fully inspect the constant velocity boots. There are several things to look for which will help you to diagnose a boot that may fail soon or that has already failed.
Step 5: Check for a cracking constant velocity boot. Using the flashlight, you will need to look closely at the boot.
In between the ridges it is common for the boot to start to crack after years of use. If it is starting to crack, then it’s a good idea to replace the boot before it actually fails.
Step 6: Check for leaking CV boot clamps. It is a good idea to take a close look at the clamps that hold the ends of the boot to the axle.
These clamps can come loose over time and the grease can begin to leak from them. If it is caught early enough, the clamps themselves can be replaced to preserve the boot and the axle.
Step 7: Check for a torn constant velocity boot. If the boot is torn and is leaking grease, then it will need to be replaced.
The boot holds in the grease and keeps dirt out.
Step 8: Check for a torn boot with dirt in the joint. If the CV boot is torn and there is dirt in the joint, then the entire constant velocity axle needs to be replaced.
Once dirt gets into the joint, it will cause the joint bearings to wear excessively and the axle to fail.
These visual checks can be performed at any time and can typically assist you in diagnosing a failed boot, so that it can be replaced before the entire constant velocity axle fails. There are other telltale signs of a failing axle such as a loud, clicking noise when turning a corner. That is an indication that the axle needs to be replaced. If you find that you need a CV boot or an axle assembly, then consider enlisting the assistance of one of YourMechanic’s certified mechanics that can diagnose and replace the CV boot for you.