Sudden failures of constant velocity joints are rare, but CV joints do wear out and may fail as a result of loss of lubrication or grease contamination (usually due to a failed boot). A CV joint that is failing usually produces various symptoms:
CV JOINT INSPECTION & BOOT REPLACEMENT
The first things that should always be checked are the boots around all four CV joints on a FWD car or minivan. The boots should be inspected for splits, cracks, tears, punctures, abrasion damage and loose or missing clamps. Damaged boots should be replaced as soon as possible because continuing to drive with a damaged boot is asking for trouble. If the grease inside has not been lost or contaminated yet, it soon will be. This will quickly ruin the constant velocity joint if it has not already suffered damage.
Replacing a damaged boot with a one-piece OEM style or aftermarket boot is a job because the halfshaft must be removed from the vehicle. Axle removal is necessary because the CV joint must first be pulled off the shaft so the new boot can be installed. An alternative here is to replace the damaged boot with a split-boot repair kit.
A split-boot (also called a Quick Boot) does not require axle removal and can be installed with the shaft and joint in place. It is a quick fix approach that saves a lot of labor and time. But the boot seam must be carefully glued to assure a leak-free bond, and the boot must not be disturbed while the adhesive cures (typically 30 to 60 minutes or more depending on the temperature and application). Other types of split boots have small screws that hold the seal together. Neither type of split-boot will be as durable or as long-lived as a one-piece boot, but for a temporary fix they work well enough. A split-boot may also be a more affordable alternative to replacing the halfshaft, knuckle and wheel bearing if the outer CV joint won't push back through the knuckle because of severe corrosion (a problem I recently encountered on an old car of mine).
The only problem with the CV split-boot that I see is finding one in a parts stores. Many stores used to stock them but they are hard-to-find these days. One source I found on the internet is www.thecvman.com. They sell the CV split-boot repair kits for about $24.95 plus shipping. Another source is Autozone.
Torn CV joint boot. This is bad news for the joint
because it allows grease to leak out, and dirt and water to
get in. Joint failure soon follows once a boot starts to leak.
When a boot has failed, there is always some uncertainly about the condition of the CV joint and whether or not it has become contaminated with dirt and/or suffered wear or damage. If the joint is making noise, the joint is obviously history and needs to be replaced. But what if it is not making noise? Is it safe to install a split-boot or to replace the original boot and reuse the joint?
Most boot failures are not discovered until long after the failure has occurred. The bad boot may not be notice until the vehicle is being serviced or until somebody is investigating the cause of a noise or vibration problem. Consequently, by the time the bad boot is found, the joint may already be dry and/or contaminated by dirt.
If the grease from inside a damaged boot feels gritty when rubbed between the fingers, the grease and joint are contaminated. The joint needs to be cleaned and inspected, and the grease needs to be replaced. Cleaning a joint while it is still in the vehicle is difficult. There are aerosol solvents and similar products for this purpose, but the most thorough way to clean a CV joint is to remove and disassemble it. Once the joint has been taken apart, it can be inspected for wear or damage that cannot be seen from the outside.
CV JOINT DISASSEMBLY & INSPECTION
Disassembling a CV joint is not difficult if you know how. The first trick is getting the CV joint off the end of the axle shaft. Some joints just pull off while others are held with a snap ring or lock ring which must first be released.
Once the joint is off, it can be disassembled by tilting the inner race to one side. This is done by inserting a dowel or similar tool into the splines of the inner shaft and tilting the race as far as it will go to one side. This will expose one of the balls which can be popped out of its cage window with a small screwdriver. The inner race is then tilted to opposite side so the next ball can be removed, and so on until all the balls have been removed from their cage windows. The cage can now be rotated sideways allowing it and the inner race to be removed from the housing.
What to look for: nicks, gouges, cracks, spalling, roughness, flaking, etc. on the surface of the balls or tracks in the inner and outer races. The cage windows should also be inspected for dimples, wear or cracks. Each ball should fit snugly in its respective cage window because looseness here is what often causes the clicking or popping noises associated with a worn CV joint.
CV joints are precision fit assemblies, so the balls should be kept in order so they can be reassembled in their same respective positions as before. Each ball and track develop a unique wear pattern as the joint ages, so mixing up the balls may change tolerances and create problems that did not exist before the joint was disassembled.
If the CV joint shows no wear or damage, it should be okay to reuse. If it does not pass inspection or is obviously defective, it needs to be replaced. Either way, before the CV joint goes back on the shaft it should be packed with CV joint grease (never ordinary chassis grease!). Special grease is usually provided with the replacement boot along with instructions on how to pack the joint. About a third of the grease is typically packed into the joint, and the rest is put inside the boot before it goes on to serve as a reservoir for the joint. There is some debate as to how much the grease actually moves around inside the joint and boot as the vehicle is being driven, but it is there for a purpose so it should be used.
When the new boot is installed over the joint, it must be properly positioned on both joint and housing. Most boots have a lip on the inside diameter of both ends that fits into a groove on both parts to assure a tight seal. Installed boots must not be crimped, twisted or collapsed. If the boot is not in its normal shape, loosen a clamp and "burp" it by carefully sliding a screwdriver between the boot lip and driveshaft or joint housing. This should allow enough air into the boot to return it to its normal shape.
Boot clamps must be installed according to vehicle manufacturer instructions or instructions provided with the replacement boot or joint. Some types of clamps require special tightening/crimping tools while others do not.
Other items that should also be inspected:
CV JOINT REPLACEMENT
When a CV joint has failed and needs to be replaced, there are a variety of replacement options: new joints, remanufactured joints and complete replacement shaft assemblies with new and/or remanufactured joints. Many professional installers prefer complete shaft assemblies because they eliminate the mess of changing individual joints and save installation time. Many shafts also have a lifetime warranty, which eliminates worries about comebacks (or at least covers the replacement cost & labor).
The degree of difficulty to remove a halfshaft from a FWD vehicle varies considerably from application to another. Some applications require special tools. Separating the lower ball joint from the steering knuckle may require a ball joint puller or fork. Pushing the outer CV joint stub shaft back through the wheel hub often takes a special puller. On some Japanese applications, the shaft must be pressed out which often damages the wheel bearings. On some cars, the inner CV joint stub shafts are retained in the transaxle by a circlip and may not pull out without the help of an axle puller. Some older Chrysler applications even require removing a cover on the transaxle so a retaining clip inside the differential can be released before the shafts can be pulled out. Some applications (older Ford Escorts, for example) also require the use of a pilot tool (or removing only one shaft at a time) to prevent the differential gears from slipping out of position.
The general procedure goes as follows:
1. Loosen the axle hub nut with the wheel on the ground using a breaker bar or torque wrench. An impact wrench should not be used because the hammering can damage an otherwise good CV joint as well as the differential gears in the transaxle. The brakes should be applied to keep the car from rocking. On vehicles where the hub nut has been staked to hold it in position, DO NOT attempt to unstake the nut. Just turn it off.
NOTE: Most vehicle manufacturers recommend replacing the axle hub nut. Once used, the nut loses its ability to retain torque. So the old nut should be discarded and replaced with a new one.
2. Raise the vehicle and support it under the chassis crossmember or side rails so the front suspension can hang free. The wheel can now be removed.
3. What comes next depends on how the inner CV joint is attached to the transaxle:
If the joint is bolted to a stub shaft (such as the cross groove Rzeppa joint found on many imports), disconnect the inner CV joint first and then separate the outer joint from the steering knuckle hub. On many GM applications, the inboard CV joint stub shaft is retained in the differential gear by a circlip (except on the left hand side of automatics). To pull the shaft out, a special slide hammer axle puller tool is needed.
If the inner joint "plugs into" the transaxle and the stub shaft is part of the joint housing (tripod plunge joint and double-offset Rzeppa joints) the outer joint must be disconnected from the steering knuckle before the inner joint can be pulled out of the transaxle.
To separate the outer CV joint from the knuckle, one end of the knuckle (the lower ball joint or the MacPherson strut) must be disconnected so there will be enough clearance to push the outer CV stub shaft back through the knuckle.
On those applications where it is easiest to disconnect the knuckle from the strut (GM for example) it will be necessary to disconnect the brake hose clip and to remove the brake caliper from its mount.
On applications where disconnecting the ball joint is the path of least resistance (Ford and Chrysler for example) it may also be necessary to disconnect the sway bar from the lower control arm and/or the tie rod from the steering knuckle.
Once the knuckle is free to swing out, the end of the halfshaft can be pushed back through the wheel hub (a puller may be needed for this step). DO NOT pound on the end of the shaft as doing so may damage the wheel bearings, the splines in the hub, the differential gears or either CV joint.
As soon as the end of the shaft is free, DO NOT let it hang. Support it with a piece of wire until the inboard joint can be removed or unbolted from the transaxle. Allowing the halfshaft to hang or pulling on it will pull the inboard joint apart.
Installing the shaft is just the reverse. Once everything is back together and the wheel is in place, the lug nuts and hub nut should be installed and tightened to specifications using a torque wrench (not an impact gun unless torque limiting sockets are used).
More FWD & CV-Joint Articles:CV Joint Basics, Part 1
FWD Quick Reference Guide
Inspecting Constant Velocity Joints & Halfshafts
How CV Joints are Remachined
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