TheSamba.com :: View topic - c-v joints vs. u joints?

Sun Jan 14, 2007 12:38 pm

What is stronger, cv joint or u-joints?
Use at extreme angles in off roading.

Sun Jan 14, 2007 12:47 pm

U-joints, but in my opinion they are over-kill for anything except race cars and all the glamis show buggies. The U-joints can handle high HP but if you are running that much HP then a transaxle is going to become the weak-link. Of all the offroad cars I have seen/driven anything over 300-350 HP should be front engine. Just my opinion though, some people like the feel of a car that looses steering ability when on the gas :roll:

Sun Jan 14, 2007 9:57 pm

At shallow angles I'd call it a toss-up. When high angularity comes into the picture a UJ starts loosing ground. The elliptical travel path of the UJ caps in the driveshaft starts to cause minor over-center like conditions. If the power is high enough this will try to lock-out rotation & twist off the ears of either the driveshaft or of the yoke or flange.

The heaviest high Torque all wheel drive or front wheel drive I can think of are the GMC motorhomes of the early to late 70's. Roughly 12,000lbs with an Olds 455c.i. for power (real late models got 403's). Both half-shafts use a CV joint on both ends. Inners are a Rzeppa type (similar to ACVW IRS) and the outers are tri-pod type.

Sun Jan 14, 2007 10:18 pm

Off road racers used to run UJ's. Now it's nearly exclusively 930+ CV's. Can't recall the last time I saw a UJ in a race buggy. Even the guy out of Nor CA or points further north with the chain driven class 10 uses CV's.

Sun Jan 14, 2007 11:46 pm

UJs. By the time you buy 300M axles, Race prep joints w/ chromo cages, and... you could have these. http://highangledriveline.com/sandrails.html Good up to 40 degrees!

Mon Jan 15, 2007 7:42 am

Kraut_n_Rice wrote: UJs. By the time you buy 300M axles, Race prep joints w/ chromo cages, and... you could have these. http://highangledriveline.com/sandrails.html Good up to 40 degrees!
935's out of the box are good to equal or more than that. If you're not racing then the std 1045/1144 alloy halfshafts should give a suitable lifespan. Those are ~$85 each. Have you priced Jesse's parts? He makes good stuff, but he doesn't give it away either.
It's no accident that Class 1 cars and the mega HP mega travel sand buggies use CV's. UJ's used to be THE answer, but they no longer are.

Mon Jan 15, 2007 8:49 am

Alot of the"Mega HP mega travel sand buggies" are going to these. For people already running 930s this seems to be the ticket for strength and travel. You could switch to 934-5s w/ a mid board set-up, but the price tag just went way up. I just have the basic "Beanie Boy" kit on my car, so it's not like I'm saying "I have them and they are great". I could seee someone breaking a few cv's or getting tired of dealing with the the servicing wanting to switch to these. What's another G when you already have 75K into it?

Mon Jan 15, 2007 9:16 am

I've yet to see any of the C1's try it. Not say they haven't looked at them as I don't travel in those circles.
Years ago the Datsun Z car half-shafts were the hot ticket. Discovery of the 930's killed that. And the 930's are not the outer limit of CV's either.

Mon Jan 15, 2007 11:04 am

I thought I had seen a class one with U-joints but this Jimco is what I saw and after looking again I think it has non-plunging 30 series joints. I know U-joints have the issue of wanting to spin at different speeds but I thought they were still stronger pound for pound. :?: Either way I am still not sold on them.

Mon Jan 15, 2007 12:30 pm

That telescoping shaft design was to address the CV's not having enough plunge to deal with the halfshaft's length delta in cycling. I never understood why a traditional square splined slip-yoke (as used in the UJ type halfshafts) couldn't be used.

Mon Jan 15, 2007 6:33 pm

Yes, that is why I had assumed it was a ujoint axle at first glance because obviously the u-joint will not plunge when the length from flange to flange changes. It seems all a little too complicated of a way to build a better mouse trap. The beauty of the VW style axle and CV is in it's simplicity. One part transfers power, allows angle change and axle length change as it rotates.

Compared to a usual, solid round metal axle, would the increased inertial mass of a slip yolk design cause more problems for the transaxle internals (like the ring and pinion)? Or is the extra weight close enough to the axis of rotation that it is insignificant?

Mon Jan 15, 2007 7:27 pm

Projectile Motion wrote:
Compared to a usual, solid round metal axle, would the increased inertial mass of a slip yolk design cause more problems for the transaxle internals (like the ring and pinion)? Or is the extra weight close enough to the axis of rotation that it is insignificant?
Comapred to a 37" Baja, Insignificant. Compared to a 1650 Padla-Trac, still Insignificant.

I=1/2(mr^2)

eFunda

Mon Jan 15, 2007 7:43 pm

Duh. I forgot about the tires and wheels and all that junk :oops:

What I was thinking was a solid shaft would be I=1/2mr^2 and the outer side of the slip-yoke would increase as I=1/2M(Rinner^2+Router^2) with M>m and R(inner and outer)>r. I over thought and forgot the basics.

Bad typo in my post too. A slip yolk sounds more like a kitchen accident than a car part.

Nice link by the way. Better than stumbling through my math and Physics books.