CV Joints

Constant velocity joints, otherwise commonly called CV joints are found in a large portion of modern cars and trucks. They are used mostly in drivetrain applications, typically for axles and drive shafts. A CV joint is used to connect a rotating and moving assembly like the suspension of a car to an output element, like a transmission or differential while maintaining a constant speed (or velocity). CV joints create a flexible and strong connection between two moving parts (IE, the fixed transmission and a suspension spindle moving up and down over a bumpy road) without sacrificing the rotating power needed to move the car forward. In this article, we are going to go over how to take apart, service and inspect a CV joint and its related components for damage and wear.

We are all probably familiar with the pain that is a failed CV joint or CV boot, the huge mess of grease, clicking sounds and binding are all unwelcome signs that it may be time to service an axle or drive shaft. CV joints typically fail when the rubber boot that keeps dirt and grime out of the joint becomes old and brittle. The boot may develop a tear or crack, resulting in a greasy mess on the inside of a wheel or underside of the car. The joint is packed with a thick grease that helps lubricate the constantly rotating and moving parts of the joint. When the boot fails, this grease is forced out of the joint due to the centrifugal forces acting on it. In the absence of grease, dirt and other road debris make their way in between the ball bearings, this results in an excessive amount of wear on the bearings and race. If left for a long period of time, the joint will become pitted and ruined, as the required smooth operation can no longer occur. In particularly bad cases, the metal wear can be so excessive that a binding and popping sound can be heard when the steering wheel is at full lock. If you notice grease on the inner barrels of your wheels, you can bet it’s time to replace the CV boot and or service the axle.

Once you have removed the axle or other damaged part from the car, rebuilding the CV joint can be very easy. You will need some basic tools like a pair of needle nose pliers, flat head screwdriver and in some cases a set of C-clip plyers. Other useful tools are a set of jaw pullers and a vice. When servicing a CV joint, the bare minimum required is a new CV boot and grease kit, typically these will include the required clamps and washers (Should you need them). Make sure you have the right kit before you take the parts off the car, so as to avoid unnecessary downtime. With the CV joint in place on a workbench or in a vice, the first step is to clean the old existing grease off thoroughly. Expect to use a few paper towels or shop rags to get this bit done. Once the majority of the grease has been removed, you can now determine how the actual joint is secured to the splined shaft of either the axle or drive shaft. Typically axles will have a c clip that is simply pressed on, with a good hammer or set of jaw pullers, the joint can be removed and separated from the shaft. However, in some cases, the axle or joint may be secured to the shaft with a snap ring, which will require the use of snap ring pliers (circlip plyers). Carefully inspect the center section of the shaft at the CV joint to determine what type of clip you have. Once you have pulled or whacked the CV joint off the shaft, you can remove the old worn boot, it will slide over the shaft and off the end. Make sure to snip or undo any clamps holding the boot to the joint or shaft before trying to remove it. With the shaft and joint separated, the inspection of the joint is next.

To inspect a CV joint for wear correctly, all the old residue grease must be removed, wiped off and cleaned out of the four parts of the CV joint. The CV joint is made up of an outer housing, inner center section (with splines for the shaft), ball bearings and a metal cage (commonly called the race). After cleaning each of these parts off carefully so as not to damage the metal surfaces, inspect them for signs of wear. This can look like anything from a change in the surface of the metal to a deep groove in the outer housing and other components the ball bearings ride on. In the pictures below, you can see the CV joint is no longer usable, as the ball bearings have worn deep gouges into the outer and inner sections of the joint. In this case, a new joint is needed. However if your joint only shows minimal wear, you can reuse it without a problem. You will just need to repack the joint with fresh grease and a new rubber boot. Once you have cleaned and inspected the joint for wear, you can put it back together. Its easiest to do this without any grease, so don’t apply the grease until the joint is fully assembled and reinstalled on the shaft. Assembling the CV joint can take a bit of finesse, start by getting the outer, inner and cage all in place. Once these are relatively lined up, start to push the ball bearings in one by one, working your way around the joint, they will only fit and work one way, so make sure you go slowly and keep track of how the joint came apart. To get the ball bearings back in place, you will have to angle the cage and center section while aligning the ball bearings with the grooves in the outer section of the joint. Once all the bearings are reinstalled, slide the boot and then the CV joint over the splined shaft and press fit or reinstall the retaining clip. Then fill the joint with the new grease and reinstall it on the car. Done and done.



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