7t2vette

Not just the joint, but the whole CV joint & solid halfshaft.

Mike Ward

A hollow tube of the same weight as a solid shaft can take far more torque. That's why driveshafts are fat tubes and not skinny solid rods.

wcsinx

Correct, CV joints won't work with the longitudinal loads imposed by the fact that the halfshaft in a C3's rear suspension also serves as the upper strut rod. And when you think about it, a CV joint really is designed not to handle longitudinal loads.

They don't. They're actually both heavier and weaker. The advantage of CV joints is right there in their name. "Constant" velocity ... unlike CV joints, u-joints accelerate and decelerate twice per rotation and the farther you articulate that joint, the more pronounced this affect is.

but ... I not would expect someone who refers to axles as "bars" to understand these concepts.

7t2vette

You should write to GM then to tell them they are doing it wrong, because every new Corvette, including the 638hp ZR1 has those type of halfshafts!!

They must have some type of advantage over the old style, otherwise why would they use them in their top performance car, as well as their other performance oriented IRS cars?

wcsinx

Non sequitur

What Mike said is correct.

As I mentioned, CV joints are not used to add strength nor save weight. They are disadvantaged in both respects to comparable u-joints.

In fact, for high power and/or off-road applications, it's not uncommon to convert CV joint axles to U-joints.

TheSkunkWorks

Oh, dude meant CV's. I had no idea what he was on about.

No, they won't work with the C2/C3 driveline/suspension layout without 1) relieving the axle shafts of their role as upper links by installing some system of additional ones, and 2) adapting/matching available hardware up with flanged inner yokes and the outer stub flanges. It's entirely plausible, and I've done a bit of homework on this one myself as part of a larger concept, but such kit isn't exactly the sort of thing you'll likely ever be able to buy off the shelf.

FWIW, there are CV's in the aftermarket rated to 900 HP and higher, and can be found on the back end of many a modern formula car.

7t2vette

Still doesn't give a reason why GM, and most others I believe, use them. We are talking about this application in a Corvette, so your off-road example is also non sequitur because I don't think too many vettes go off road intentionally!

So, if they are so inferior to u-joints, then why are they pretty much universally used by every auto manufacturer in modern cars?

wcsinx

I never said they were inferior. I said their advantage is right there in the name, "constant velocity". When you weigh all options and take into consideration typical usage, that's a good enough reason to go with such a design.

wcsinx

And those joints probably cost more than your average econobox.

I once heard a very wise man say, "The systems used on F1 cars have about as much in common with street cars as a duck does with a bowling ball."

vettehardt

Because it is cheaper!

jyounane

Precisely. CV joints are predominantly used in FWD cars where large steering angles would generate unacceptable acceleration and deceleration per revolution... no big problem when wheels are pointing straight ahead. Not needed at all in RWD Corvette where angles are minimum.

Joe

TheSkunkWorks

That's a fair observation. I figured out a while ago this would be a very expensive mod to pull off successfully, as it's one thing to dream up cool stuff and quite another to make it happen. Still, if I were able to build a no holds barred C3 it would be on my list.


BTW, C6...

7t2vette

Well, for the auto industry to universally accept them in IRS applications, I have to believe that the advantages outweigh the disadvantages. Technology moves forward, not back. Even the most expensive exotic cars with IRS use them, there has got to be good reason for it.

Quite possibly, and wouldn't surprise me! This is an interesting topic, I am going to ask a person I consider very knowledgeable about this, the owner of a race shop that builds serious road race C5 and C6 Corvettes, which is local to me. These guys know their stuff:

Powell Raceshop



Me too!

wcsinx

Did you miss the part where I mentioned that converting CV jointed to axles to U-joints is a very common mod for more extreme applications?

TheSkunkWorks

Before the inertia thing gets completely lost, a CV can be heavier than a half-shaft and still have a lower moment...

Solid LT1

CV's have less rotating friction compared to the Hooke's joints used in our C3's there may be a 0.25% increase in fuel mileage in replacement, and with gas at $4.00 a gallon it would take a long time to amortize that expenditure.

Love that the guy can't use "spell check" and typical attitude of the youth of America today.... They already knew that

I forgot, one other advantage, if you want to go to a 4wheel steering system, they will work over a wider range of miss-alignment too......May as well go with a trans axel swap too.....

wcsinx

There are a few brave fabricators that have added a true upper strut rod, and then "converted" the half shaft to slip joint (i.e. removed the retaining ring) I don't personally feel like a CV joint conversion would buy you much more than that, but it would be an interesting project to be sure.

7t2vette

No, I didn't miss that, but what does that have to do with this disscussion? You are comparing apples to oranges. Unless I am mistaken, this disscussion isn't about "extreme" applications, such as a very high hp/tq purpose-built IRS drag car, it is about the use of cv joints in the average to above average street IRS car.........such as the above average production C6 ZR1, or any other high hp performance vehicle in production today with an IRS!!! No one uses u-joints anymore for this purpose. I am not an automotive engineer, nor do I pretend to be, but today's performance vehicles using CV joints with IRS are engineered to last and not break, and I can't argue with that!

That being said, I do know several people that have very high rwhp/tq C5 and C6's (including one C5 that is in the 1200rwhp range) that do not have an issue with breaking cv joints or the halfshafts, and these cars are not babied in any way.....but these cars are street driven and/or road raced only and not drag raced with slicks, which is where breakage is much more likely to happen.

On a chassis dyno, the drivetrain losses on our cars are much, much higher than that of a C5 or C6, and I have to believe that the CV joints play a part in that.

wcsinx

You're really not listening are you. Both setups have advantages and disadvantages. You keep trying to make a case for "it's-better-cause-it's-newer" (rather like the OP), and that simply isn't the case here. I'll say it again. CV to U-joint conversions are commonplace.

And I assure you they are not using stock components.

Then you believe incorrectly. A U-joint will only exhibit significantly more rotational resistance when it's driving at an angle. When it's nearly straight as it would be on a dyno, there's hardly any difference.

PeteZO6

Yep, when straight, or nearly so, there should be no loss of HP. Another point I don't think has been mentioned: how well can a CV joint withstand axial loads.

We know the U-joints can as our half-shafts are under constant compression in the normal state. C5/6 half-shafts have one CV joint that is made to allow axial movement - the axle can be compressed and extended as the suspension moves up and down. Knowing that, you couldn't just use a C5/6 half-shaft as-is, you'd have to replace one CV joint (the one that extends and compresses) with a standard CV. As I mentioned in my early posts, the cost of modifying the half-shafts to fit a C3 would be pretty high. Only a determined guy with a shop with all the machine tools at his disposal would try it. It would have to be a labor of love, because the cost wold be beyond any advantage of the CV setup.

Pete