Constant velocity joints (popularly referred to as CV joints) are special universal joints found on automobiles used to transmit motion from the gearbox to the road wheels.
Whether the car is front-wheel drive, rear-wheel drive or driven by all 4 wheels, the cv joints will be used to transmit power in any of the options given above.
Without the cv joint, it would be impossible for a front-wheel vehicle to transmit power to the wheels while taking a corner.it is therefore important to reckon that the primary role of a cv joint is to transmit power through the driving shaft at all-wheel angles without varying the initial speed hence the name constant velocity joint. In simple terms, it ensures that whether the wheel has steered 70 degrees, nothing stops the wheel from rotating.
You may ask yourself, why should there be a need for a rear cv joint for the rear tyres yet the steering wheel is only coupled to the front wheels? Well, the vertical movement of the body of the vehicle when it is loaded or when it goes through a bump alters the inclination of the wheel known as camber. This slight movement means the drive shaft must accommodate for this small variation otherwise there will not be turning force to the rear wheels. All this stretching and compressing is catered for by the cv joints.
For each shaft on every wheel, there are 2 cv joints. One on the inside of the shaft and the other on the outside of the same shaft. Each of the cv joints is splined internally to the shaft. The splines allow the cv joints to move in or out depending on the task ahead.
Each of the cv joints is parked with a special grease to keep the splines and the ball bearings lubricated at all times. Boot rubbers cover all the ends of the shafts to secure the grease from spillage or contamination from dust on the road.
There is no special care for cv joints. However, failing to take good care of them can easily render the car immobile.
Below are the most common problems associated with cv joints
Heavy take off: Accelerating too much while taking off or when taking tight corners stretches the boot rubber and may cause it to overstretch which leads it to puncture. Once it's punctured the grease may spill off leaving the cv joint to run dry hence its failure. Sometimes water may enter through the punctured holes and wash away all the required.
Use of zip ties: most mechanics after replacing the boot rubbers, use plastic zip ties commonly known as tie wraps to secure boot rubbers. Unknown to them when these plastic zip ties get heated up due to cornering, they expand and snap off leaving all the grease to escape from the cv joint. Once the cv joint runs dry it is just several days before it fails its normal operation.
Periodic maintenance. The grease inside the cv joint is not to be replaced unless the dust boot is punctured. Never open the securing seals on the boot rubber in the effort of wanting to see if the grease is dirty. The grease is lifetime unless acted upon by external force i.e puncture etc. You may never achieve the tight seal machine finish for the clips.
If the dust boot does not have any signs of damage, then it doesn't warrant any replacement.
Use of correct rubber boot: trial and error method on dust boot rubber dies not to work. Too small or too big will cause more havoc to the ball bearings. A small dust boot rubber will shred in the next 2 corners leaving all the grease to spill out. A size boot rubber wi not hold more grease for your shafts instead the clips will not create a tight seal. Hot grease is very thin which makes it very vulnerable to sip through the clip gaps.
Always make a habit of checking out underneath your car at least once every 3months. This way you may be able to arrest any arising situations on your cv before it's too bad. Cv joints are very expensive to buy. In fact, in many cases buying a brand new cv is way beyond reach, people prefer getting a second-hand complete shaft.
SIGNS OF A FAULTY CV JOINT
- When taking a tight corner, say towards the right, the cv joint on the right side produces a "Tak tak tak " harmonic sound that is easilly noticeable by all the vehicles occupants and even passersby. The worn-out cv joint is the one on the side you are steering the vehicle towards.
- In most cases vibrations when driving has been associated with wheel balancing or disk skimming. Worn out cv joints also can cause serious steering vibrations. In the past, mechanics have tried wheel balancing, disks skimming or even replaced bushes but vibrations never went away. In such scenarios only cv joints are the culprits.