does anyone have a broken cv they could send me for some analysis? cage/carrier and *****, etc.

for those people who break CV's often, can you please shortly explain when it happens, and show pictures if you have them of the failures. if no pics, please try to describe where the break occurs.

thank you.


Modified by dfoxengr at 8:38 AM 1/4/2008

 

Failures I have had:

Drag launch at the track, the axle broke at the joint (boot). X2
Over time the joint became sloppy from autoX & road coarse abuse.
Failure at the joint from old age on a couple beaters.
Damaged axle nut threads from repeated removal & install.

Failures I have heard and seen pictures of:

Axle snapped off at the tranny. This is a bitch to remove.

 

- Wore out joint, makes noise.
- Cut the boot somehow (!?!?!) maybe debris. Axle grease everywhere.
- Snapped off axle at the hub when hitting another car wheel-to-wheel.
- More worn-out joints.

No design issues or suspension geometry issues here, just normal wear and tear.

-Chris

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris F &raquo;</TD></TR><TR><TD CLASS="quote">- Wore out joint, makes noise.
- Cut the boot somehow (!?!?!) maybe debris. Axle grease everywhere.
- Snapped off axle at the hub when hitting another car wheel-to-wheel.
- More worn-out joints.

No design issues or suspension geometry issues here, just normal wear and tear.

-Chris</TD></TR></TABLE>
If you don't mind, would you elaborate on the noises that would indicate a CV shaft failure? ( at cost of replacement)

I get a weird scraping-like noise when applying light-moderate throttle at lower RPMs around 1.5 to 2k....at about 2.5k to 3k rpm it goes away.

 

I broke a bunch this year on my roadrace car. They all broke the outer joint. Pulling apart the inner joint, the tripod bearings left marks on the housing where the axle bottomed out under compression.

The outer joint bearing cage got ripped apart. You usually feel a vibration for about 1-2 laps and a pull to one side right before they come apart.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris F &raquo;</TD></TR><TR><TD CLASS="quote">
- Cut the boot somehow (!?!?!) maybe debris. Axle grease everywhere.

</TD></TR></TABLE>

This has happened to me many times. Have learned my lesson about using only OE axle boots.

 

Boot failures are common. Only other I have experience is the inner tripod housing fracturing, probably due to age.

Julian

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackdc5 &raquo;</TD></TR><TR><TD CLASS="quote">
If you don't mind, would you elaborate on the noises that would indicate a CV shaft failure? ( at cost of replacement)

I get a weird scraping-like noise when applying light-moderate throttle at lower RPMs around 1.5 to 2k....at about 2.5k to 3k rpm it goes away.</TD></TR></TABLE>

As CV joints wear out you'll hear a popping sound while making tight turns, which will get louder and louder until they finally break. It takes awhile for them to fail completely.

Failure on the other hand means the car is not going anywhere. It's broken and immobilized. The engine will rev in gear and the car will not move...time to shut her down and cool down so you can pop a new axle in. If you have the right tools you can change an axle in less than 10 minutes. You can replace one for $70-100.

The sound you describe does not sound like CV shaft failure. Is the sound coming from the dust shields on the front brakes? Sometimes small stones will lodge between the rotor and the shield making scraping sounds.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by clemsonhatch &raquo;</TD></TR><TR><TD CLASS="quote">

As CV joints wear out you'll hear a popping sound while making tight turns, which will get louder and louder until they finally break. It takes awhile for them to fail completely.
</TD></TR></TABLE>

Yes, *and* sometimes you'll get one that makes horrible sounds at WOT in a straight line. Popping/thudding sounds that can shudder the car. LSD chatter sometimes is the same feeling, almost.

 

anyone else.

thank you

 

ok so i looked at Mikey3000's cv shaft.

i wante to do some quick calculations to see if he was exceeding the limits of the shaft.

t=Tc/J

t is the shear stress in psi
T is the torque in in-lb
c is the outter radius(root spline radius) in in.
J is the moment of inertia in in^4 for a solid shaft J=1/2*pi*r^4

t=(440 ft-lb)*(12in/ft)*(.5in.-.075in.) / (1/2*3.14*0.425in^4)=43787psi

these are DSS 3.9 axles which DSS says is good for 600HP. they are made from 300M.

300M properties
http://www.matweb.com/search/d...19365
with an tensile yield strength of ~240000 psi

this is all assuming no shock loading, stress raisers, a stress intensity factor, and of course this strength figure was made in tension.

ive always used the figure that shear strength is 60% of the minimum tensile strength, so this means that in shear 300M has a shear strength of 144000 psi


so as a STATIC safety factor, these axles, for this motor would be
144000/43787=3.288

so with shock loading and the introduction of the stress raisers(spline roots)
we can probably assume that it doesnt take much to break these like he did.

basically, a bigger or stronger axle/material need be used in his application.

the break was also clean, on a plane perfectly perpendicular to the axis of the shaft, which indicates a ductile material. this could make me think that the shaft was not properly heat treated after being made since a material with that high of a UTS would be brittle and that would give a break similar to the ones that are jagged and on a plane at a 45 degree angle to the axis of the shaft.

it could also indicate that even if it were heat treated properly, and of the material specs claimed, that a large shock loading occured (not "preloading" when launching) this is more likely the case since thats what he told me.

there were also small very thin raised grooves around the circumference of the broken shaft. these are called shear lips and the thinner they are, the higher the stress intensity factor was that incurred the break.

the splines were also twisted right at the break which makes me believe that on a launch before the break occured, the shaft was twisted and deformed beyond the elastic limit. this could have contributed to the break later on.

thank you all for reading, and hopefully you learned something.

-derek

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dfoxengr &raquo;</TD></TR><TR><TD CLASS="quote">for those people who break CV's often, can you please shortly explain when it happens, and show pictures if you have them of the failures. if no pics, please try to describe where the break occurs.</TD></TR></TABLE>

I suspect that nobody on here has broken as many CV/half-shafts as me. They are a definate weak spot on the Honda/Acuras, although you're likely to never or perhaps rarely encounter problems on the street or even in most forms of racing.

I'd show some photos, but photos of broken CVs are basically just some ripped boots and a lot of grease. They have to be thouroughly cleaned in order to get any detail at what has happened.

What fails: almost always it is the outer cv, more specifically the actual carrier. Typically they explode or crack in half. I did have an axle shear once, although that was most likely due to a machining issue because it really shouldn't have sheared there.

In my experience all or some of these conditions must be present to have a catastrophic CV failure:

Torque. In our cars, this mostly means RPM. You have to have sufficient torque to break the carrier/joint, which requires the car to be in it's powerband, near peak torque.

Angle. The CVs are actually pretty strong--but mostly only if they are not when they are highly mis-aligned or at the extreme end of their range. Basically if you have the wheel cranked, you're much more likely to experience a catastrophic failure. In extreme cases, you can actually take a little bit of steering out of the rack by putting some washers in by the inner CVs, which will prevent the most extreme steering angles. Typically in a race car you don't need to be out at full lock anyway (we're not parallel parking), so nothing is really lost by doing this.

Shock. This is the most important factor. If you're spinning the wheels (on say gravel) and then instantly get traction (on say some broken pavement), you're going to have a good chance at exploding a joint/carrier. Large bumps and/or jumps as well as rubbing of the fenderwells can also contribute to this 'shock' effect.

Angle can actually contibute to shock in a big way: creating the trifecta of exploding CVs:
If you are cranked over (angle) and hit a bump/jump, the tire may come into contact with the fenderwell and basically stop the wheel (shock), while the axle is still rotating at high RPM (torque). Instant catastrophic failure.


Some guys I've talked to say that heat, quality of grease, and even pressure in the boot can contribute. But in my experience, they haven't been nearly as big a factor. One thing that does seem to matter is "seasoned" axles that have a fair bit of mielage on them seem to last much longer.

This is all from first-hand experiencing breaking about 10 Honda/Acura CVs in competition vehicles.

 

thanks rotten.
i would really like to take a look at some one's broken cage/carrier sometime.
i would be able to find the initial start of the cracks that caused the break, and i would also like to look for stress raisers in the cages that could be removed in order to extend their life

 

I might be able to send you one.

 

thank you and let me know
-derek