Anyone know much about metallurgy?

[daepp]

I don't! This is a broken rear axle from a 26K lb '08 International flatbed. We've had them break nearer to the wheel, which we attributed to overloading, but this one broke at the diff.

I'm wanting to know if this is just par for the course on older vehicles, or maybe it was overloaded? Driver inexperience (they intentionally drive over a lot of curbs delivering to future homesites - might have used too much force or torque)?

It's already been replaced - I like to learn from mistakes whenever possible.

[MBAtarga]

Paging Lubemaster, pelican member Lubemaster - please report to this thread.

Okay - so that was his old name - he goes by M.D. Holloway now....

[TimT]

First two pics show corrosion at or near the root of the splines....

Cant say the failure is lube related...

[masraum]

Originally Posted by TimT

First two pics show corrosion at or near the root of the splines....

Cant say the failure is lube related...

No, but MD Lubey knows a think or two about metal failure.

Hmm MD Lubey, maybe we should call him Doc Lubey.

[wdfifteen]

The apparent corrosion is troublesome. It appears to have limited the axle's strength But there is no fretting, so no fatigue. This was loaded beyond it's capacity and was good one instant and broke the next. The question is, how much was it's capacity reduced by the corroded area.

[Gogar]

I hope that axle has signed the appropriate model release forms.

[daepp]

Can you describe what you're seeing as corroded?

[masraum]

I'm guessing that the beige area is what WD was calling corrosion. If that isn't from the axle being dropped on something, then I think it's an indication of a bad spot (imperfection, crack, etc...) that created a weakness that was the ultimate cause of the break.

[daepp]

I didn't notice that before. It was repaired at a job site so I suspect that's dirt.

[wdfifteen]

What do the rest of the splines look like? The weakest part of a floating axle is the spline area. Are they twisted at all? I'm still thinking overload.

[fanaudical]

I agree that this failed quickly since there is little evidence of crack propogation prior to failure. This shaft experienced too much torque relatively quickly. What's the other end look like?

[Evans, Marv]

I agree with the excessive torque. It looks a lot like a drive shaft spline I broke off once using too much power.

[Porchdog]

Excess load, likely an impact. The driver knows how it happened, even if he isn't saying.

Those splines are almost certainly hardened - a great location to propagate the failure.

Were there a lot of miles on the axle? That's not a very surprising failure after long service. If it were mine I would replace the other side.

As the others have said, there is no sign of progressive failure.

[aschen]

Im no expert but looks like a pure torque overload ethier single event or fatigue. The 45deg angle is always torque overload. Im not sure if there is anything to indicate a material issues

Torsional Fatigue Failure - Identification, Diagnosis and Prevention - Reliabilityweb: A Culture of Reliability

[harvardma]

There are beach marks so it is a fatigue failure.

[Hugh R]

No expert here, but the splines look like they were too loose to begin with and it caused slop in the whole system. As others said, massive torque applied, but to a loose spline to begin with. Chinese parts? On my Son's 72 Olds Cutlass, it ate three sets of front wheel bearings from Kragen in a year, they were all Chinese. I've replaced/repacked over 100 front wheel bearings/races and never had this kind of failure. I eventually got real American made ones from NAPA and never had another problem.

When doing overhead rigging for events, we strongly suggest Crosby (American made) rigging components, Nobody worth his salt in Hollywood rigs with stuff that says "China, India, Pakistan".

[wdfifteen]

Off topic a bit, but when I was interviewing George Montgomery for the book he told me stories about what they had to do to keep their drag racing cars together back in the early days of hot rodding. The development of speed parts was incremental - the didn't make race parts until there was a market for them. George was always at the bleeding edge and parts manufacturers couldn't keep up with him.
Anyway, he was often stripping the splines on the Cadillac rear axle he was using in his Willys gasser. The splines were the weakest part of the axle. His solution was to turn the rest of the axle down so it was less stiff. The torsional displacement of the axle cushioned the shock load on the splines enough to keep them from stripping. He painted the axle and scribed a straight line down its length. After every race weekend he took the axles out and checked them for twist. A few thousands in twist and he replaced the axle.

[masraum]

Originally Posted by wdfifteen

Off topic a bit, but when I was interviewing George Montgomery for the book he told me stories about what they had to do to keep their drag racing cars together back in the early days of hot rodding. The development of speed parts was incremental - the didn't make race parts until there was a market for them. George was always at the bleeding edge and parts manufacturers couldn't keep up with him.
Anyway, he was often stripping the splines on the Cadillac rear axle he was using in his Willys gasser. The splines were the weakest part of the axle. His solution was to turn the rest of the axle down so it was less stiff. The torsional displacement of the axle cushioned the shock load on the splines enough to keep them from stripping. He painted the axle and scribed a straight line down its length. After every race weekend he took the axles out and checked them for twist. A few thousands in twist and he replaced the axle.

Cool story, thx.

[Porchdog]

Originally Posted by harvardma

There are beach marks so it is a fatigue failure.

I don't see beach marks.

The geometry is pretty much classic for a torsional failure. Those striations radiate out from the initiation point. The rough grain structure at the center suggests that it was a single event - hence my suggestion that the driver knew what the immediate cause was.

Assuming that his was an older part, I suspect that you have found the endurance limit.

[daepp]

He is a new driver. I suspect the rear wheels of the fully loaded truck were up against a curb and he dropped the cluck in his inexperience.

Thanks for all the great info. I think a little training my be necessary here.