Checking Constant Velocity (CV) Joints

Posted in Car Care on June 18, 2018

Car owners need to add an important visual check to their maintenance schedule when they become owners of a front-wheel-drive vehicle: the constant velocity (CV) joint. Here's why.

What is a CV Joint?

The heart of every front-wheel-drive unit is the constant velocity (CV) joint. This clever device transmits engine power to the front wheels. Unlike the simple U-joint of rear-wheel-drive vehicles, the CV joint must transmit power through two different angles — up and down through the range of suspension travel, and side to side through the entire range of steering angles.

If you look under the front of your car, you’ll see a pair of accordion-ribbed rubber boots connected to each front wheel. The four CV joints are inside these boots which are packed with grease and tightly sealed. The accordion bellows allow the rubber boots to flex through the angles and changes in length that the joint must go through.

Both the boots and the CV joint have to survive for many years and tens of thousands of miles in an incredibly hostile environment — hot. cold, wet, snow, ice, salt, stones, potholes and plenty of neglect. That they hold up as well as they do is why I'd rate the CV joint as a first class piece of engineering and technology.

So what can go wrong?

The biggest enemy of CV joints is boot failure. A CV joint will quickly fail if it lacks proper lubrication or is exposed to road din, salt and debris.

The boot may split from fatigue, and vehicles operated in extremely cold weather are especially susceptible to boot failure on those sub-zero days. And of course rocks, potholes and other “object’ d’roadway” can tear the boot.

Inspect your CV joints regularly

Ever since the 1980’s, the world’s car makers in their quest for more fuel efficient vehicles, have turned to smaller, front-wheel-drive cars.

The key to making the CV joints last the life of your car is to visually inspect the rubber boots at least every three months. Every time you change oil, look for evidence of grease leakage from the boots. Typically, a boot will begin to fail by cracking in the valley of one of the “Vs,” By turning the steering all the way to the lock and slowly rotating the wheel, you can inspect the boots carefully.

Even a quick inspection is helpful. Look for any evidence of grease on the outside of the boot or sprayed onto the surrounding suspension components. If everything is completely dry, the boot is most likely intact. But if there is any doubt, take a closer look.

What if the boot has failed?

It’s time to remove the drive axle and disassemble the CV joint for cleaning and inspection. It's not a DIY job and it’s not cheap, and the sooner this is done after discovering a torn boot, the better your chances of keeping the repair hill down.

Once removed, and after a thorough degreasing, the joint can be checked for excess wear or play. If the joint isn’t damaged. it can be repacked with grease and a new boot fitted. If replacement is called for, you’ll be looking at several hundred dollars additional in parts and labor.

Audible Warnings

Listen for clicking or clunking noises from the drive shaft as you turn or accelerate. These noises indicate that the lack of grease and contamination from road grit have the CV joint on the road to certain failure.

Can the boot be replaced without removing the axle?

Yes, but we don’t recommend it. There are replacement boots that feature a seam so that the boot can be installed without removing the axle — this seam is the replacement boot’s weak point. If they really worked well the manufacturers would use them, and they don’t. More importantly, if the original boot has failed, the joint needs to be thoroughly cleaned and repacked with grease, something that cannot be done without removing the axle.

Should the CV joint be repacked periodically?

Not in most cases. Check your owner’s manual. Most manufacturers recommend periodic inspection only, and don’t suggest disassembly unless the boot has failed. Some car makers do suggest cleaning and repacking at specific intervals, so follow their recommendations.