20 replies to this topic

[FTodaro]

I have heard of he Half Shafts failing, where they pull them selves apart, but never had seen the actual shaft itself fracture into two parts.

 

This past weekend Brian Murdick lost a half shaft, at Mid O, no contact damage no hits to the left rear. Just shifting gears and lost power. I built this car so i know it well, nothing unusual about the half shaft, I did rebuild it by putting replacing the OEM Grease.

 

If you are not familiar with this, you are looking at the hub side of the half shaft, there is a grove there where a C clip holds the end of the half shaft together it snapped at that grove.

 

Any one see a failure like this?

 

 Half Shaft1.JPG   181.1KB   11 downloads

 

 Half Shaft2.JPG   148.38KB   8 downloads

 

 

[Ron Alan]

Yes...happened to me...exact same thing...no drive! And to clarify this is inside the cv joint on the wheel side. Once it brakes the cv joint can pull apart. No idea why this happened or happens. In my case it was a new(old)junkyard axle. Was only on track a short time. Grease seemed fine.

 

One thing to note based on memory...is the snap ring on this a different size then lets say the one that goes on the end of the axle in the differential? Maybe in reassemble the wrong size was used? Just a thought...

[38bfast]

Yea that one suprised me as well. I talked to Drago and he said he had one do that on his car as well.

Good thing you replaced the diff just in case.

[LarryKing]

The problem is that you rebuilt it. You can have to 20 year old component that will last 300,000 miles... until you try to fix it.

[Michael Novak]

We had it happen last year. Did you replace the c Clip by chance....   The C clip let the cv shaft come out.

[FTodaro]

The problem is that you rebuilt it. You can have to 20 year old component that will last 300,000 miles... until you try to fix it.

I disagree, all i did was put in new grease.

 

We had it happen last year. Did you replace the c Clip by chance....   The C clip let the cv shaft come out.

I did not replace the c clip, but the c clip did not fail or give way, the shaft broke where the c clip holds the end so the c clip was good.

to good.

[David L]

You may have thought the clip was good but this is most certainly the result of the shaft not being fully seated in the cv joint. 

[Michael Novak]

The C-Clip let the shaft come out enough and it broke off at the weakest spot..  Maybe it just broke---But I would bet the CV was most of the way out when it broke.

[Jim Drago]

You may have thought the clip was good but this is most certainly the result of the shaft not being fully seated in the cv joint. 

correct, thats what happened to mine at Mid Ohio a fews ago as well

[SaulSpeedwell]

Torque and "shock" (2nd, 3rd, 4th, derivative of rotational acceleration, depending on which smartass engineer you ask) is what it is.  The grabby Hoosiers, grabby clutches, and Insta-Shift driver phenomenon aren't helping,  20 year old/150K mile/Multiple Race Season stuff is being subjected to many multiples of its original design intent.  Put in stock clutches and 185/70-14 All-Season Sears RhinoGrips, and I *PROMISE* you that things will (almost) stop breaking and (most of) you will have even more fun (most of the time).

 

Having said that - I always hammer those "C clips" on an anvil for additional interference/retention.  Stub axles popping out is not cool when less than a quart of lifeblood is keeping things from seizing. 

 

The axle has no reason for wanting to break at the point shown, except for the stress risers located in the "C-clip" groove.  Unless it "popped" out and the whole load was being carried by that end?  Else, the torque (and "shock") was even throughout the shaft, unless something twisted, which it apparently didn't?  As said elsewhere, treat the axle like any other high RPM load-carrying racecar part - buy it right, check it for cracks, polish it, radius it, balance it, play symphony music to it at night, do anything you can to make it last.  And then buy spares. 

[SaulSpeedwell]

I disagree, all i did was put in new grease.

 

You used BMW grease, didn't you, Frank?  That stuff makes everything break!

[RWP80000]

From the picture, it is apparent the spline'd shaft at time of failure was not engaged into the female CV joint splines any deeper than the button end itself resulting in all of the torque being transmitted to the outer CV joint through only this small button shaped end piece. This resulted in the pure torsional (twist) failure/separation pictured at the stress riser groove machined for the shaft retaining clip.

 

Had the spline'd shaft been fully engaged into the female CV joint splines per design, the button portion of the shaft would not receive any torsional (twist) load application due to the button end being beyond the female CV joint splines once the lock clip passed through splines to the point where expands for the purpose of preventing the shaft from disengaging the CV joint female splines. In the design position, there would be no way for the button to be twisted off the end of the shaft through the clip grove.

 

There are a number of possible contributors to this failure;

 

a.) The shaft may never have been installed any deeper than the depth of the button.

b.)The shaft may have been installed deeper than just the button but not deep enough to allow the clip to expand.

c.) The clip may have been missing, wrong or defective preventing it from performing its function. 

d.) The female spline'd CV inner race may have been installed backward so the relieved side intended for ring expansion was facing the wrong side of the CV joint, (I have not confirmed that this can be done- just a supposition)

 

Either b, c) or d) could result in potential for the shaft to be extracted during vehicle operation from the CV joint female splines to the point of only engagement of the button portion of splines resulting in the shaft being engaged as in condition a) which is required for this failure. 

 

Rich Powers

SM 145-Arizona

[davew]

I have seen this a couple times. Both times on well used, untouched OEM axles with lots of street miles. And, lots of race miles. Sometimes stuff just breaks

[FTodaro]

I think I am going to have to put this one on me.

 

I took a closer look after looking at the posts. The C clip is still inside the splined housing, about 1/4 of an inch from the edge. So the C clip did not fail. It would appear that I did not fully seat the shaft and  C clip past the edge of the housing to lock it. Not sure how the C clip ended up coming off the shaft and staying inside the spline housing but that is where i found it.

[lillyweld]

Still, all good stuff to know. Thanks for sharing, Frank.

[Ron Alan]

The "C" clip holds the male/female splines in the correct position. Because the clip can compress or squeeze this allows the male/female portions to separate. It normally takes a "shock" type blow to achieve the compression of the C clip.

 

I think there are 2 common reasons why the C clip can compress and allow the male/female portions to move. First is when attempting to remove an axle from the upright...those brave enough to hit the end of an axle(brass hammer or big steel)without damaging to bad can cause a shock wave that can cause the C clip to compress and the splines in the CV joint move(5 balls on a pendulum)

The other is when people try to remove the axle from the diff by pulling on the top of the upright. When you do this you are trying to compress 3 C clips...1 in the diff and 2 in the CV joints. 

 

In general the rubber boot of the CV joint will keep the male splines from completely coming out of the female(they will if you really stretch the rubber). It is very possible to dislodge the C clip and have no idea. I think you can pull the male portion out of the female just to that point where the C clip expands and does not allow the male to re-enter the female(without compressing the clip)but there is enough tension to hold the male splines just in that 1st 1/4".  

[Ron Alan]

Hmmm...other than the intended design of each CV joint to articulate and move in and out I dont think the physical dimensions of each piece and the final resting place of the snap rings in a properly assembled axle allow for any length difference? Are you saying the rubber boot which keeps grease in and is designed to stretch/flex with the CV joint is strong enough to change the length if not installed properly?

It would seem the 35mm range sited above is the normal amount of movement the CV joints allow? 

Sorry, I'm just struggling to understand how one of these axles can be shortened or lengthened intentionally...the inner snap rings(of CV joints) land in one spot and one spot only, After that the rest of the parts are designed to move and the boot keeps the grease in.