Very basic cv joints question

[Nico911]

I'm telling you, this one is very basic : what cv joints are for ??

I read a lot about them in this forum but can't figure what they do...

[Reifle]

Keep your wheels turning and move with the suspension

[pete3799]

They allow the axle to to change angle with the suspension.
They're basically u-joints.

[Nico911]

Great. And what are the symptoms of worn cv joints ?

[Noah930]

You can hear clicking coming from the rear axles.

Each of our cars has 4 CV joints. There is one at each end of each rear axle halfshaft. They allow for some "play" so that the engine/transmission can apply power to the rear wheels while still allowing for suspension travel to the rear wheels. Each CV joint is comprised of two discs (or "cages") between which are ball bearings (the size of grapes). The whole thing is slathered in grease, which is held in place by rubber "boots." Over time, and particularly if the rubber boots tear and the grease gets flung out (and lets in dirt/grime), the metal ball bearings within the CV joint wear. There's increased slop in the driveline and you may hear that as clicking coming from the worn CV joint.

[chris_seven]

The couplings in any drive shaft have to deal with radial, parallel and axial misalignment and this can be dealt with in a number of ways.

Universal joints or Hooke Joints have some capability and are commonly used in the propshafts that connect gear boxes and axles but the have some issues.

The speed of rotation of this type of joint is non-uniform as if it runs at an angle. This change of speed will generate a torque in the shaft that is being used.

It is common practice to use two Hooke Joints at 90 degrees to each other to cancel out this torque.

The other issues is that this type of joint doesn't readily accommodate the changes in length needed when used as a drive shaft.

Propshafts use a sliding spline to achieve this objective but splines don't slip until you have overcome the locked in torque and fairly high axial loads can be generated.

In a car using a prop the differential and gearbox have relatively good thrust capability and can deal with these forces.

The transmission on a 911 wouldn't manage to deal with this force and this explains the use of the extra hinge in the early Nadella shafts used on 64/65 911s (I believe it was used up to 1968 on cars fitted with an LSD).

The CV or Constant Velocity Joint allows articulation to occur without producing a torque. By designing a joint with 'plunge' the shaft can also change length without a significant axial force being developed.

[OsoMoore]

I disassembled one of my CV joints to clean and repack it in grease. You can see the pics here: https://drive.google.com/folderview?id=0B3Pw5qvi2hRrYllOb1ZVYTNHYms&usp=sharing

It is not a hard job, to work on joints, but it is very messy with grease everywhere.

[will hung]

When you work on it, get yourself new hex head sockets, make sure they are installed in the bolts, and then kind of press them in toward the bolt when turning the head. Otherwise you'll strip the bolt head and then an easy job becomes a very hard job.

If your inner cv joint is going bad, you'll feel vibration on acceleration. If the outers are going bad, you'll hear clicking.

[frannyB]

They also allow for the distance between the wheel and the differential to change. As the suspension allows the rear wheel to move up and down, and since the differential drive flange isn't moving with it, the distance between the two will change. You can grab your axle and slide it in and out somewhat and you'll see the movement. Very clever those CV joints.

They are also on every front wheel drive car to allow the wheels to turn with the steering wheel. Just listen when you are out and about and you'll probably hear that tell-tail clicking when some poor old Honda that has never had any maintenance makes a sharp turn. So sad...

On the bright side, they are pretty easily repaired/replaced and since every car has several of them, not all that expensive

Franny