How strong are CV halfshafts?

[Guest Anonymous]

Hi all,

 

I just broke a ujoint type halfshaft in my '71 240 last week. I didn't break a joint, it was the shaft itself. I understand the cv joint shafts are stronger. How much so? Is it worth converting over to those?

[Guest zline]

Hi all' date='

 

I just broke a ujoint type halfshaft in my '71 240 last week. I didn't break a joint, it was the shaft itself. I understand the cv joint shafts are stronger. How much so? Is it worth converting over to those?[/quote']

 

Hell yeah its worth it !! Ross will get you Z31T cv and a 4 piston front brake kit for a really reasonable price the + outweigh the - unmistakably..you 1, get a 5 lug pattern 2, a super strong and newer CV setup 3, larger brake capability.

 

and who says no to bigger brakes?

[fl327]

cv's are weaker than halfshafts, but can take my angluraity than a halfshaft. most of the time they go is when you lower a z and start beating on it, the funny angles over time wears em out, one of the reasons i refuse to lower my car.

[stony]

cv's are weaker than halfshafts, but can take my angluraity than a halfshaft

 

Im not to sure this is true. if your talking the axles them selves maybe true but when your talking cv joints and ujoints i think the cvs are better. Only when you talking about the z ujoints and all the aftermarket and stock replacement stuff on the market. cvs are made of some kind of hardened steel where all the ujoints i broke looked like they were made out of some kind of pot metal.

[blueovalz]

I have to agree with Stony. I raised my R200 high enough (had to dimple the subframe crossmember over the back of the diff for clearance) so that axles were in optimal geometric position. Squat was included in the final positioning so that the axles were just slightly drooping leaving the differential when the car was at rest. This way, under light load the axles were straight, and under heavy acceleration, they were only slightly raised upward out of the differential. I still broke the joints. Then I switched to the CV jointed axles and never broke another in 10 years.

[jeromio]

The stock ujointed half-shafts do incorporate a kind of CV joint. The shafts change length - there's an inner and an outer portion that slide back and forth while maintaining "Constant Velocity". For instance, the shaft that connects the the trans output to the transfer case input on my truck is referred to as a CV shaft. It looks just like a larger version of the standard Z half-shaft.

 

But it's ancient technology and inherently weaker than an equivalent solid shaft. With the CV jointed shafts - the modern ones that are sourced in this case from a ZXturbo - the change in length is taken care of by the ball bearing tripode joint. In this design, the moveable part, the CV joint, is the weak point, not the shaft. As Stony mentions, these CVs are typically made from machined, hardened materials. It may boil down to an apples to oranges comparo since the materials and tolerances employed in the old design likely do not measure up. Then again, most all cars now employ solid shafts with CV joints and none use the old style shafts.

 

As Cyrus proved, the shafts of the UJointed halfshafts are certainly breakable. I'm guessing that with modern CV jointed shafts, the CV will break before the shaft. Or possibly the stub axle - if only (IMO) because that part is going to be older and has likely seen millions of heat cycles over it's 30 years of use.

 

I've seen broken CV joints, broken UJoints, pictures of broken stub axles and pictures of broken UJointed shafts. But I've never seen a broken CV jointed shaft. So, they don't exist in my world

[Guest Anonymous]

Ok, sounds like maybe I need to go for the CV shaft conversion. Are CV shafts expensive?

[fl327]

i still think its when you lower the car is when halfshafts are in danger

[Pop N Wood]

I have been reading posts about U joints vs. CV joints for quite some time and I have yet to read anything that I would consider a definitive answer one way or the other.

 

About the only thing everyone seems to agree on is that CV joints handle angularity better than the U joints, and that the U joints without the grease zerk appears to be stronger than the one with the zerk.

 

Arguments about which is the better or a more modern design are really irrelavent as far as strength goes. A CV joint designed for a low power application (say a Huyndai) will not be as strong as one designed for something like a Peterbuilt. Thus the only question that matters is which of the two available for my Z is stronger?

 

Unless I missed the posting where someone listed Nissan's official torque ratings of both parts or did some type of controlled testing, then all we have to go by is people's past experience. And if you look back through the archives, I don't think you could make a case that one is clearly better than the other.

 

Not throwing down a challange. Just saying the answer is not clear.

 

[fl327]

i would have to say that the more you modify the z suspension, the more angularity comes into play, if you leave it closer to stock, i think the issue is a lot less. then you have v8 torque on a modified suspension, where angularity begins to increase, and the need for a cv increases as well. i know at least one 11 second z car that runs halfshafts and has no issues, but he does have the ones with no zerk fittings in the cross, he runs nissan units, and has had no probems, but he is an automatic, but he runs halfshafts behind a supercharged 355 with a 700r4, probably be a little different with a stick.

[blueovalz]

The angularity is of prime importance here. And as opined, there may indeed be no strength advantage between the two when considered against zero angularity. During the period that I investigated the use of CV joints ('88), I was told on more than one occasion that under high torque loads, the U-joint is pretty reliable up to about 7 degrees mismatch. I was also told that the CV joint (the tripod design in particular) was reliable for about twice that angle. The typical caged ball design (popular with the German autos) is good well beyond 20 degrees. This is why I was experimenting with the German design when I found out the Turbo ZX shafts were nearly "bolt on". The 911 joints I was going to use were good up to over 400ft/lbs of torque, and the 930 joints have held up to 800lb/ft of torque. I have only recently began looking into these again mainly because of their simplicity in adapter plates and their compact design eliminates sway bar/joint interference that I've found is on my application.

[Guest 240hybrid]

I dont have any hardcore facts, but I would think that CVs would be stronger that U-jointed type halfshafts, being that all car manufacturers got away from the oldschool U-jointed shaft and moved on to the new CV shafts due to strength reasons. Also I've heard many more stories of U-jointed halfshaft failures, than CV shafts failures on high HP setups. One of the stories thought to be failure of the CV turn out to be failure/shearing of the bolts connecting them to the companion flanges. Goes to show that if the bolts connecting the flanges together fail before the CV joints do, those CV joints must be pretty stout!

 

As for both CV and U-jointed shafts if you increase the angle on them, you put them under more stress. Being that if you increase the angle, you lose some leverage and to compensate for this lose, more power is required to complete the same job. Everybody knows that power/force follows the path of least resistance. That path of least resistance being the CV/U-joints, and these forces being transferred increases friction, and heat, and are eventually turned into STRESS resulting from the angle. Example....you take either a CV or U-joint shaft and turn it without any angle it turns with little power needing to be applied, and if you increase the angle it gets harder to turn the shaft and more power is necessary. Just my $0.02

Chase

[Guest zline]

Ok, sounds like maybe I need to go for the CV shaft conversion. Are CV shafts expensive?

 

no not at all ! Ross will hook you up nicely

 

 

http://www.modern-motorsports.com check his website out

[jeromio]

Right. If you could adapt the UJointed CV shaft from my truck to a Z car, I'm sure that'd be plenty strong. Or shafts from a Vette - them gots ujoints too. But either of those are pretty difficult to adapt. Much easier to go with ZXt CV shafts.

 

I had bad info above: the sliding shaft should not be called a CV shaft. I guess that's some BS I picked up from 4X4 discussion (or at least that's my excuse ).

 

Digging around, I found an article here that goes into some engineering. CV joints are dubbed thusly because Cardan type Ujoints do not rotate with constant velocity when the joint is angled:

If there are 2 joints in perfect phase (parallel), then most all of this differential in velocity is eliminated (although I'm not sure that's true in the Z Car rear susp.).

 

This article only briefly mentions CV joints. There are 2 types: tripot and Rzeppa. I've never taken apart my ZXt shafts. Rzeppa is the balls and cage style. These are discussed as being 5 times stronger than the tripot kind, which do not, according to this article, have the strength capabilities of Ujoints.

 

I'm not sure about the inner, diff. side joint on the ZXt shafts - I suspect that's a ball/cage style. I've never taken mine apart. That outer joint sure looks like a tripot (tripod, tripode?) type though.

 

At any rate, I am very confident that the minor cost difference (about $75) that I coughed up to switch to CV shafts vs. new Ujoints was well worth it.

 

Now, imagine how much actual homework/studying I could've accomplished had I not been procrastinating, looking all this up?

[stony]

both sides of the 300z z31 shafts are the ball and cage type.

[Scottie-GNZ]

One of the reasons why there appears to be no definite answer is because we are dealing mostly with used parts making it a crapshoot. You cannot expect every 20+ yr old CV pulled out of a J/Y to be perfect. The solid u-joint makes the halfshaft a strong unit but like Terry has said several times, angularity plays a big role in how well it holds up.

 

If you run the car hard with lots of squat, you cannot go wrong with the CV setup. I advise against rebuilt CVs because, like Stony said, the cage is made of pot-metal, probably where all the Yugos have gone . Get a pair of CVs and a spare pass side. To show how much of a crapshoot it is, I broke a CV, the drivers side which is not the side that is suppose to break.

[Guest Anonymous]

Ok, I've emailed MM through their site and explained the situation. Hopefully they'll get back to me today with some prices.

[jeffp]

I really dont understand why there is so much discussion on the matter. When you look at the configuration of the standard universal typ half shaft and compair that to the CV shaft what you finf is at least 30 % more material on the universal part of the shaft. The CV 280ZXT shaft has three roller bearing type setups in each side of the shaft. They are very srtong. The universal type shaft has only two bearingg spindles and a needle bearing cap.

There shopuld not be any question which is stronger, its just a matter of looking at the two to determine there is MORE contact material on the CV then the universal setup.

Also. for that matter, I would NEVER consider running that shaft on my car, and last dyno pull got mr 473 fppt pounds of torque in 4th gear. Would any of you like to try that with the universal type half shaft and really depend on it?? I know I would not.

anyway just my thoughts on the matter, and they sure have worked out well for me.

[Guest Anonymous]

Ok, I'm a little ignorant. I get the impression there are 3 shafts-the ujoint type I have, a later model CV type, and a different CV type out of turbo cars. I also gather that the turbo CV type is the strongest, and is the type I should be going to. Is this correct? (just in case I didn't make it clear earlier, the shaft itself broke on my ujoint-type, not a ujoint.

[blueovalz]

I'm not going to claim one type of shaft is stronger than the other. I know that I broke three U-joints (OEM, one poor, and one very good aftermarket) before I finally started using the ZX turbo CV jointed shafts. I've not had a single failure since then. For the Z with the R200, there are only 2 practical shafts: OEM U-jointed ones, and the swappable (with some minor work and parts) 280ZX Turbo shafts.