Mechanics

CV Axle Joint

This article explain how an automotive CV joint works. This information pertains to all front wheel drive and independent suspension vehicles.


CV Joint Axle and Boot

A CV joint (constant velocity) joint is a type of multi-ball flex joint that connects two fixed rotating shafts and is designed to transfer force from the transmission to the drive tries. Theses joints have a range of motion that is more broad than conventional U joints. CV joints are also designed to deliver engine torque evenly throughout their range of motion were as U joints give isolated movement in extreme angles.

Consisting of a series of hardened metal balls encased within a housing while using an inner metal cross (center) in which the axle is connected. These joints can be disassembled and inspected by removing the axle and forcing the inner cross beyond center. This will allow the balls to be removed and reassembled. Once serviced a graphite based grease is needed to properly lubricate the joint. A rubber boot is used to prevent grease from being thrown out of the joint while in operation. Once a boot has failed it should be repaired to prevent failure and a more costly repair.

Service on this style of joint is minimal for the exception of a visual inspection the joint will continue to operate until failure. The first signs of failure include clicking while turning under power and vibration under acceleration. The CV axle must be removed and inspect by checking the range of motion and looking for any rough spots in the motion. Some manufacturers design the joint to be replaced as a full axle only.

History

There are other types of flexible couplings such as a Thomas or Oldham joint. These joints use a rubber fiber flex material and are mainly used for drivelines and not axle shaft joints. These joints gave out under pressure which warranted the inventions of the CV and U joint. There is no known inventor of these joints.

Common Problems

  • CV joints fail causing acceleration bind up.
  • CV boot fail allowing grease to leak out warranting replacement.

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-23)