I understand U-joints but how is a CV different ?

 

its stronger and takes an angle better, essentially its a ball in socket joint, with some large "ball bearings" for lack of a better word. its hard for me to describe exactly

here are some pics!!

 

^^ Knows what he is talking about.

 

ok i wont go as far as saying its stronger but it can take a certain degree of angle better.

 

I would not say stronger either.

All axle shafts (besides yota's samurais) have u-joints. I have CTM u-joints which are the strongest u-joints out. I broke a stock CV axle with my stock tires, in mud...very low traction.

All driveshafts have u-joints, some have "CV" double cardan u-joints. Our stock driveshafts wear the fawk out when you put a lift on them because the "CV" type joint at the t-case cannot operate worth a damn at an angle like that.

Now heavy duty type CV joints, can't find a pic, but they just came out for D60 shafts instead of u-joints. Those are strong as hell and will bind less when turning and can turn at more of an angle than a u-joint d60.

 

The CV's I mentioned that came out for the D60's are rated stronger than a superior/CTM set-up. You have to get shafts also.

 

I thought i read the new jeep wrangler has cv joints on the driveshafts. What is the thinking behind that ? How would that be better or is it just cheaper to make ?

 

Probably driveline vibrations. Since u-joints have an arc that they travel in when they rotate, you have to phase them correctly and have them running in the same angle so they will cancel out the vibrations caused by the opposite joint.

My guess is smoother driveline operation and less maintenance. That is if the CV joints can hold up to a beating. Albeit I haven't seen any pictures of them either.

 

I've reacently discovered that many refer to a double cardan joing (basically two traditional U-joints back-to-back) as a CV joint.

But what we normally think of as a 'CV-joint' as seen in most FWD vehicles and IFS setups (like our Rangers) is a joint like Bob described. Normally it uses a series of ball-bearings that are in very accurately machined groves. The groves let the joint articulate while still transmitting rotational torque.

Here is an interesting discussion of U-joints vs CV's. It is specifically a discussion of joints for farm and work equipment, namely PTO drives off tractors, but the same applies to 4x4's. They also refer double cardan joints as 'CV-joints' for their discussion.

The important difference is that a CV-joint can tollerate a greater angle between the two shafts than a U-joint can. A U-joint will have massive wear, or more likely breakage if operated at large angles. CV's on the other hand can deal w/ greater angles. This is why solid axle vehicles can still use U-joints at the wheels. The suspension articulation has zero effect on the drive-train angle at the wheel. The only thing that changes this angle is the steering. Limiting the steering to < 15 or 20 degrees is usually not a problem. However for IFS, both the steering AND the suspension articulation result in a change in drive-axle to wheel angle. This compounding results in some much larger angles.. hence the need for a CV.

Now we could use these double cardan style CV's.. but that would cost a lot of money. The ball-in groove CV is far cheaper and lighter. Hence why you find it on almost all light-duty pickups these days.. inlcuding our Rangers.

Edit: Here is an even better discussion of traditional FWD automotive CV's.

 

In addition to the notes above the CV's being able to take greater angles during rotation, there is one other thing that's important to add...

CV, stands for Constant Velocity. When a U-Joint turns, even a double U-Joint, the output side of the joint changes (although very slightly) rotional velocity throughout each rotation. The greater the angle, the greater the change in velocity. If you look closely at how the actual U-Joint turns, you can see how the steep angles will cause the changes.

A CV will always keep the output at the same velocity as the input.

Don

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Isn't the point of a double cardan joint to solve that?! The U's are 90 degrees out of phase w/ each other, so the changes in velocity from each of the two joints cancel out. Something like that. I'm having a hard time visualizing it myself.. but that's what I (thought I) read..

 

Thats true colin. The double-cardan joints are considered a CV joint. Since the 2 seperate u-joints phasing cancels out the "velocity" changes of the opposing u-joint.

Rzeppa type CV joints are at the outer end of our CV's. They do not allow lateral movement of the joint.



The inner joint is a tripod joint. It has (obviously) a "tripod" with bearings on the outside of each shaft on the tripod. It's outer-race has 3 grooves machined for the tripod to travel in. This joint is the one that allows later movement (in and out for compression and extension of the suspension that must allow the CV axle length to change).

 

just for the record, i was mistaken when i said CVs were stronger, i was thinking of a dual cardan joint when i said that, but the pics are correct for a CV joint.

 

Good information! Learn sumthin new everyday!

 

CV Shaft= Constant Velocity shaft.....always has angles & the "u joints" are constantly being "strained".

 

Ask DOC how strong CV joints are. Then ask him how much fun it is to be followed 200 yards in reverse, by Jen and a hammer...