What usually breaks the inner or the outer? I'm thinking the outer, but am wondering why people upgrade thier inners.

Has anyone ever snapped a shaft? It seems that 1st gen IFS would break a CV first.

I guess, what I'm trying to understand is the order of weakness between the following parts:

Inner CV
Outer CV
Shaft
Hub
Ring and Pinion

What is most likely to break and what is least likely to break.

I would want to build my drivetrain stronger, but not so strong as to make the ring and pinion the weak link.

In my opinion
The outer is the weak point. A lot of times, like when you saw mine go, it is not an actual break it just seperates.

I have never seen the shaft itself break.

the shaft does not usually break, it is almost always the joint itself.

When i build it, i will build it strong, until then, i'll replace the broken stuff.

So, the outer joint is the issue.
Has anyone ever seen an inner joint fail?
If not, I wonder why this is teh upgrade I see and not an outter upgrade.

My $.02...

It's always fun to devise new ways to do things. I respect the context of the thread.

Products on the market:
Warn makes the hub fuses http://products.warn.com/truck/axles/hub_fuse.shtml.
Four Wheeler Mag just put drive shaft fuses in their project Titan. They are made by www.powertrainsavers.com

To answer another question: I have seen "CV Half Shafts" break at the outer joint (the cage comes apart from over extension), the outer stub (over torque), and the middle shaft (over torque or spinning and getting traction).

So it seems like it takes a conservative 3000 ft*lb of torque to break a CV, not taking into account the turning issue.

If all of your engine torque was delivered to one front wheel, say at a 140 ft*lb at the flywheel (optimistic for a 22re)...

140 * 2.5 (4Lo t-case gearing) * 4 (1st gear) * 4.1 (diff) = roughly 6000 ft*lb. You could bust one of those no problem.

Now... with that powertrainsaver idea... when those fuses shear, does the driveshaft just drop onto the asphalt or what??

i'm a little late to the party here, but i remember reading an article about toyota CVs where they did a test to the braking point of a cv at different angles. there was a neat graph showing the CV strength versus the bending (steering) angle. it was either on roger's website (www.4crawler.com) or marlin's website (www.marlincrawler.com). i don't have time to look for it right now.

Wow, let me know when you find that. That will save me having to rip off Autozone by returning broken CVs that have had 'accelerated wear testing' performed on them.

Watch the video promo, it stays in place due to an internal sleeve.

On my Tacoma, I broke the outer shaft. I have seen the inner shaft broken on a Tacoma. I have also seen the joints fail.

A few weeks ago at the TTORA Takeover, I broke my drivers side hub when the outer shaft exploded in the hub. The same thing happened to two other guys in TX TTORA.

Ha, you must have been with my brother-in-law from Houston . . he had the exact same thing happen to his setup at Takeover . .

I heard that the frontends of the '03+ 4Runners was beefed up, anyone ever break a CV? I have heard of torn boots, but that's about it.

is your brother in law steve?

Yeah, he is . . . that poor truck has been through hell and back. He broke another axle (plus a dozen other things) last week at Spring Creek . . here are the pics:

http://034runner.blogspot.com/2006/08/blog-post_13.html

I think a lot of the carnage related to his truck is due to the Aussie locker he has up front to be honest . . . I still think a selectable locker is the best bet for IFS.

Wow... poor truck. That thing needs all the help it can get with CV breakage I'm sure.

One thing I might add that you probably all already know, but that nobody has really mentioned...

...spinning the wheels (whether spinning them on the ground, or landing under throttle) breaks shafts due to the shock load. When the wheels are spinning free and then get lots of traction (like when you land, or when your tires get a good ledge to bite into) that extra shock is what breaks them. In fact, I have heard that what makes the Longfield birfs so much stronger is that the cryo process actually softens the metal so that the shock loads don't shatter them like glass. This is counterintuitive, but if you think about it, Toyota designed the components to last forever and in doing so, they used a very hard metal to prevent wear over time. A very hard metal that works great with the components it was designed to be used with (ie a low HP engine and tiny tires.)

So Bobby reduces the hardness and the brittle ness, and wallah, you have a new birf that is softer (wears faster), but that also is much more resilient to shock loads.

Any way, the other thing nobody has really mentioned is that the further a CV is taken away from a flat plane, the greater the forces that have to be applied through the shaft to get the same force at the wheel. This applies both in the vertical plane (turning the wheel) and in the horizontal plane (flexing the shaft away from flat - whether up or down.)

Obviously when you combine the two factors (the angle of the CV, and the impact load) you have the best chance of breaking something.

I totally agree about the shockloading, but you should leave the metallurgy discussions to us metallurgists. :D

Toyota uses a "normal" heat treatment that sacrifices ductility (stretchiness) for strength - which is a normal tradeoff. This process is very well known, predictable, and cheap. The cryogenic process Bobby Long uses refines the grainsize and is a superior heat treatment to what Toyota does. It delivers BOTH higher strength and higher ductility.

Hardness is a test where a ball (or diamond pyramid) is pushed into the material, and is a direct correlation to the strength, but neglects ductility to a large degree. Since Longfields are cryo'd 4340, (a nickel-chrome-molybdenum steel alloy), I would be willing to bet that it has BOTH higher hardness/strength AND ductility, which makes it much more resistant to damage/failure than other steels.

So there you go...like I said, that is what I had heard, but you can't trust everything you hear.

BTW, I am all about the brinnel and what not. In fact, it sounds like what Bobby is doing (according to your description) is analogous to the differences between cast and forged steel - the refining of the grain orientation and whatnot - it's all molecular man...

But that's about as far as my non-metalugical-ness takes me ;)

Thanks for the clarification...

Wow, that is interesting stuff. The molecular qualities of metal are fascinating.

So it is the impulse that kills CV's and etc. rather than sheer torque load?

That is correct. I mentioned spinning and coming to a sudden stop in my original post, that is exactly what I was talking about.

It's that the torque load spikes dramatically when the "impulse" happens.


You can talk about working load all day, but you have to design for that occasional spike that breaks stuff.