CV Joints have an odd story. CV stands for Constant Velocity, meaning that the input and output spin at the same speed during every degree of revolution. The type of CV joint on our cars are mostly a Rzeppa style joint, which has an inner hub with 6 grooves in it, and an outer shell with 6 similar grooves. Six balls run in the six grooves……….. blah, blah. These CV joints are on the axles that connect the transmission or differential to the wheels. The inner CV joints have angled grooves, the outer joints have straight grooves. Some inner CV joints are a tripod type, with a three armed cross through semi circular balls with needle bearings, and an outer shell with three grooves. All joints have CV boots to keep the grease in and the dust and water out. And to mention, the Universal Joint of driveshaft fame is not Constant Velocity at any significant angle. The more you bend the shafts, the more it flops like a fish. A short and clever page in Wikipedia on CV joints might fascinate some.
Why CV Joints Fail
CV joints are packed with a grey molybdenum grease, commonly called Moly Grease. It gets old and breaks down like any other lubricant. Karmakanix uses a red synthetic grease from Amsoil that just does not ever seem to fail. The grey grease slowly turns to green water, and the joints suffer from lack of lubrication. The red grease slowly turns to peanut butter, but joints we have taken out of Vanagons with over 120,000 miles are still fine. What better testimonial could you get?
CV boots fail. Hopefully they fail early enough that your CV’s are still good. That’s one way to look at it. If your CV boots are broken, try to stay off dirt roads and avoid winter driving. The water and dirt will eventually cause the CV joint to fail. Plan on replacing those CV boots to avoid the big expense of CV joint failure.
Hard cornering and lots of U turns under power will wear down CV joints way more rapidly than taking those maneuvers a little easier. Outer CV joints are almost always the first to fail, because they have to accommodate much higher forces due to high angles during turns.
The BOLTZ! We cannot emphasize enough the need to tighten CV bolts with a torque wrench. Older 8mm CV bolts tighten to very close to their limits. We see loosened CV bolts every year. When the bolts fail, the mess includes repairing threads or replacing drive flanges. And of course, many CV joints get damaged during the breakdown.
CV joints on 4 wheel drive cars rarely fail, even at very high miles. Guess why. Karmakanix cannot remember any rear CV joints that went bad even on very high mileage Audi 4000 Quattro cars.
CV Repair: New CV Joints or Replacement Axles?
That answer is shrouded in complicated circumstances. Basically, if you have a newer car, you love it, and want to drive it for more than a couple of years, then replace any bad CV joints found during an axle repack with new Lobro CV joints. If the clunker is getting old and worthless, consider a Chinese replacement. Understand that some Chinese axles don’t fit, can start clacking after a few months, and will certainly wear out faster than Lobros. The metal simply is not as durable. Understand too, that we cannot warranty Chinese axles with the Karmakanix extended warranty.
For customers with high mileage vehicles that they really love and want to keep until retirement, it is not bad practice to replace all the CV boots and repack the CV joints with synthetic grease. Karmakanix only uses factory OE Lobro CV boots. Other aftermarket brands with German names are made in China and some of the rubber is of a poor quality. So are the axles.