The CV boots at either end of your drive axle stop dirt and water from getting into your constant velocity (CV) joints, and keep the lubricating grease from getting out. But these boots can and do fail, so how do you check if they’re in good health?
CV boots are just rubber accordions that go over the CV joints on your drive axles. They’re a $5 part at best, but if one splits and lets out all the grease it contains, you can end up with a big repair bill.
Under each CV boot is is a constant velocity joint that flexes and rotates so that drive is still provided from the drive axle to the wheel while the car goes over bumps and around corners. Without the boot, these grease-laden joints would become thick with dirt and filth and lose their ability to deal with suspension movement.
If you hear a clicking noise that is especially pronounced when tuning a corner, chances are a CV joint has gone bad. In extreme cases, if you ignore the clicking noise the CV joint can eventually fall apart. When this happens, you'll be left staring at a car that runs perfectly well, but which can't actually move itself.
- Jack It Up - You won't have decent access to the CV joints while the car is on the ground, so get it raised up and supported on jack stands. Once up, take off the relevant wheels, which should give you decent access to the drive axles and CV joints.
- Clean Up - The inner fender and front suspension will be thick with road dirt and filth, so wash the area. Don't worry too much about getting the brakes wet, but try not to get soap on the discs.
- Full Lock - Turn the steering wheel until it's on full lock. This will give you room to get your head behind the wheel hub, where you’ll be able to better see the outer CV joint boot.
- Tied Up - The CV joint boots are held in place by circular clips, either metal or plastic. Check these first. If they’re present, correct and tight that’s good. If they’re missing or if they're just a zip tie, you may well have dirt within the CV boot, or a lack of grease. Replace a missing tie asap, but not before pulling the CV joint back from the wide end to check that there’s nothing in there but grease.
- ’Box clever? - At the inner end, look for any signs of grease leaking out. Again, check the ties or clips and ensure that they’re holding the CV boot tight and in place.
- Give Them a Massage - Rubber CV boots should be pliable. If they are dry and inflexible, they don't have many miles left on them. To be sure what state they're in, pull them, twist them, push the folds apart and look into the crevices. Look for any signs of cracking or cracked rubber, and check for splits and cracks. You may not see these with just a casual glance, which is why you need to get your hands on the boots.
- Listen Closely - Spin the brake disc with the transmission in neutral. You'll often be able to hear a CV joint that is starting to go bad if you listen closely. The quiet clicking of a joint that has stated to fail is easy to miss when driving, but much more obvious from under the car with the wheel off.
- Clean, Road Test, Repeat - If you can’t see any cracks or leaks and hear no clicks, but still want to be absolutely sure, give everything a good clean and then snap a picture with your phone. Then go for a test drive, making sure to stay on clean roads and parking lots, and then have another look. Do lots of tight turns to really flex the CV joints. If there are any grease spots when you look again, you know your CV boots are weeping. Simple.
What to do next?
If you do find a leaking or torn CV joint boot, the proper course of action is to remove the entire drive axle and replace the boot, and often the CV joint, which we exmplain here. Depending on how many miles the car has on it, a rebuilt drive axle complete with CV joints and boots is likely the solution.
In a pinch, if the CV joint appears to be in okay shape otherwise, a split CV joint boot can be quickly installed. Just like they sound, split boots, or quick boots, are sliced down one side to allow them to be fitted without removing the axle. Unfortunately, even the best split boot with good adhesive to seal up the split, isn't as good as an unsplit boot.
But if you have a torn leaking boot, a split boot will keep the CV joint from going bad for a few thousand miles until you can get around to replacing the entire axle. When the time comes to replace the drive axle, you will find information in your Haynes manual, but here is a general how to - Drive Axle Removal and Replacement