suddenly breaking axles (not even moving off the line)

[Ondonti]

I have never broken an axle in the past except when something obviously lead to it (like a dry burnout wheel hop) or messed up differential shimming. I would launch on my 6200 rpm limiter with 5 pounds of boost on 24.5x8 MT's on a 6' rim. 1.72 to 1.78 60's every time.

Broke 1 non saginaw last week, replaced with saginaw (so both are saginaw) and one of them broke again. I didn't figure out which one it was yet. First break was on a 7000 rpm clutch dump (not on purpose, nervous on first megasquirt run attempt), then thinking I would be able to pay more attention to the clutch, I wired up the launch control settings and launched at only 4800 rpms this time (but probably with some boost).

Only difference I can see is that last year we were treating the slicks with VHT, and the track seems to be prepping for the midnight races (I never race the expensive day races unless it is test and tune). I know my first 11 was on a prepped surface...

I don't even move off the line. Just hear *bang* and the axle lets go. No wheel hop, nothing. just feel the bang and a slight shudder in the car as the energy dissipates. 8.5 pounds the first time, then 10.5 pounds the second time for boost levels. Never even got there

Not sure whats going on. I always dumped the clutch pretty aggressively before. I was super nervous these last 2 times and the launch control actually made me more nervous so I couldn't do anything but dump the clutch even though I kept thinking "engage it slow."

The clutch is really aggressive, ~900ft/lb holding, so it doesn't give. I am used to my tires lighting up the moment I dump the clutch and spinning throughout first gear.

At this rate I may not get a pass this year since I don't even know if I will hit the track again this year. I don't carry around spare axles because the midnight races are usually too short to bother hustling just to get 1 pass, plus if it breaks again, bah!!!!!

Here is a video of the saginaw breaking. Car moves maybe 1 inch.
The low quality axle broke the splines in the hub (and it looks like pot metal so this does not surprise me) and I am guessing the saginaw broke inside of the transmission like they have in the past.
I ran my 11.54 on that junk type axle last year.

If i could get carbon pucks on my disc I would do it because maybe my clutch is just too aggressive
I have never broken the parts that DSS upgrades. I am hoping its the drivers side axle that broke because it has a boot leak and has taken the previous years pass attempts but I never get that lucky
I will find out in the morning. While I can always lower launch control settings, in the past I was always spinning the slicks and obviously leaving pretty hard. Same exhaust set

Previous year's first pass on a prepped surface. I just feel like something is wrong that these axles are breaking all of a sudden 2 passes/trips in a row.
http://www.streetfire.net/video/ondo...---_647377.htm

[BadAssPerformance]

The low quality axle broke the splines in the hub (and it looks like pot metal so this does not surprise me) and I am guessing the saginaw broke inside of the transmission like they have in the past.
I ran my 11.54 on that junk type axle last year.
.....
I have never broken the parts that DSS upgrades.

Sounds like (A) you're making some good torque and (B) they are prepping the track better

Unfortunately at the expense of axles.

DSS axles use Chrome Moly for the shaft and the tulips (ends including splines) so yep, you have broken the parts they upgrade.

Got pics of the carnage? I snapped the splined ends off a couple then broke the u-joint and bit the bullet to get DSS axles...

[Ondonti]

I only use unequal lengthers. The Saginaws have only broken inside the trans. I had 2 failing that I caught before they broke because I pulled the axles out.

You said the ends are GKN Forged CM so, is that something DSS is just sourcing? I have a beef with DSS after they screwed Matt Monett on a couple thousand dollar set of axles the broke first pass and were not warranted. Right now I am an $19 sucker every time an axle breaks. I don't want to be a thousand dollar sucker Especially if something in my setup is going to break the axles when your setup would be fine with it (for some reason).

I would rather throw down big money on a carbon clutch disc because it would protect everything in the drivetrain from shock. The Cost of DSS is enough to finish my AWD swap so I would ditch the passenger front axle anyways.

The owner of the track was there racing a 13 second car and the people at the track were being really nice, first time ever.

[BadAssPerformance]

Yes, the ends are CM. Yes, they cost a ton.

Wow, $19 is cheap. If you dont mind changing axles, get a pair with a lifetime warranty?

[Ondonti]

Well the lifetime axles look nice (installed one in Polygon's Baron) but I don't want to find out they suck. Might go with a lifetime axle for the AWD passenger axle in the future.
Uploading pics.

Local yard has half off day and I guess with entry its about 20 bucks if I bring in my core. I just popped out the bad drivers axle. End is stuck in the transmission. I will probably have to pull the other axle so i can knock it out unless I can get uber lucky with a magnet.

Exactly the same spot the saginaws have failed for me 4 times (this being the first time to fail without something else damaging the axle like wheel hop or improperly shimmed Diff). They still all break here or begin to break and you get lucky and catch it :P







I was gonna be lazy and try to swap the axle without changing the fluid (leave car up on one side) but the fluid leaked out a bit and it looks like mercury Its been through more then one axle and the OBX sheds quite a bit.
So off to the yard and hope the 68,000 mile AA is still there (already took the passenger side).

[Ondonti]

Extra pissed that the axle broke because I was line up with my friend for the first time ever and he ripped off an 11.9 on dry rotted 22" slicks (1.9 60') that he borrowed. He didnt want to line up with me last time, but heck, I broke then too!

[RoadWarrior222]

By now you might have quite a few scars and sharp edges develop in the diff, which would be crack starters when they hit the axle splines.

[turbovanman²]

It looks like you've addressed the weaks links and now you've found the last weak link. Probably before, the clutch was slipping a bit, tires were slipping a bit, now the axle's are taking the full brunt.

[Juggy]

cryo-treating????

would this help strengthen them up?? maybe its worth a shot

[zin]

By now you might have quite a few scars and sharp edges develop in the diff, which would be crack starters when they hit the axle splines.

This is what I was thinking too... That there is something in the diff that is starting a stress riser on the axle. They don't seem to be failing at the "root" of the spline, but rather at the point they are exiting the diff. It might be helpful to smooth out the splines in the diff, just a little chamfering at the end to eliminate the sharp edges that could be initiating the crack/break.

Mike

PS Cryo might help, but in the end we can't make a race horse out of a mule... Just a really fast mule!

[Ondonti]

Well I have pictures somewhere that you can see the splints starting to flex down there and it starting to crack at each spline (caught the axle before it broke) That was from when the Diff was loose in the housing (bad shim job).

This axle seems to have the same issue but it "finished" :P

When I go AWD the OBX can't be used anymore so I guess I can inspect it for stress risers. At this point its not something to address.

I feel sharp edges on the diff are not an issue because even when the diff was loose, the axles didnt have damage on the splines beyond the cracks. No surface damage.
I will look for the picture, I am sure its uploaded somewhere. I hate looking through my old imageshack. Stupid thing sucks at loading up the pictures.
If not I have them on my desktop. I am pretty sure I even posted the pictures before.

I think the outside of the shaft is failing then the failure moves towards the center and the axle fails.
I don't know if that means you need to harden the outside better or if cryo would be any good.

[Ondonti]

Okay so I don't know if i was correct in there being no damage. You can see where the diff splines are pinching on the axle. But remember that the diff was improperly shimmed so it was loosed and moving around, probably why you see those pinch marks. It also just might be the effect of the diff splines supporting the axle splines that are engaged while the exposed splines are failing as the axle twists internally.

You can see that it fails on every spline as the splined end inside the diff twists farther then the rest of the shaft. Obviously the diff is not completely engaged into the splines but I dont know that this is an issue since our oem spider gears are probably just as narrow and I am sure the Quaiffe is the same.

So anyone have ideas on a treatment that would prevent this? You can see the 2 completely busted axles seem to be the same problem but taken to the end of the road


Wheel hop Failure. Didn't completely snap until I tried to launch, but there was no loud bang because it was obviously already "done"
This is last year.


Here is how a junk axle breaks.

[turbovanman²]

Weird, your the first OBX'er to do this that I know off, doubt its the OBX. I haven't twisted mine yet but it is an auto.

I would say its simply the weakest link in your setup now,

[Ondonti]

Look up, I just added the picture of a junk axle and how it fails. That is the hub side splines but you can see its a completely different type of failure. Obviously a huge difference in the material.

Err actually these are the shaft splines that go into the outer tripod. This why a better shaft helps the junk axles.

[BadAssPerformance]

Treatment is not going to help much if the base metal is not capable of getting any better from the treatment, like trying to heat treat low carbon steel wont make it much harder or stronger as not enough carbon...

This is why chrome moly is good for axles, the chromium and molybdenum add resistence to shock and it is medium carbon so it has some springyness.

[blk86trbo]

Anyone ever tried "gun drilling" them? I've heard of people with pulling tractors doing that to axle shafts...something to do with a tube having more torsional strength than a solid bar because of the increased surface area

[RoadWarrior222]

Well that sounds odd, unless there's a surface hardening treatment applied, then it's like a hardened sleeve inside it I guess.

Edit: if we're into the treatments I think the idea of BBQing them then peeing on them for shadetree nitriding is one of my fave ideas

[zin]

In this picture it looks like the load might have been concentrated at the point of failure, rather than being spread out the length of the splines, initiating cracks with predictable results... OR, the axle is too hard/brittle and just can't take the shock/torque. If it is the latter, Cryo treatment of that part would make it as good as the material will let it be. I'd also suggest a light polishing job, the kind of treatment you'd give a rod, not removing material so much as smoothing out sharp edges to reduce the stress risers... shot peening might help, but it might disturb the fit of the splines, making them too loose...

Wheel hop Failure. Didn't completely snap until I tried to launch, but there was no loud bang because it was obviously already "done"
This is last year.


Here is how a junk axle breaks.

That one looks like straight-up materials/heat treat failure...

Mike

[BadAssPerformance]

Most axles are only case hardened... so the outer surface where the splines are is hard but the inside core is not so it allows it to twist off like this... well this one is not off, but looks like it was caught just before doing so

[Ondonti]

BTW I realized that I changed from the 8 lb aluminum fidanza to full 18 lb steel flywheel to protect my center mains/crankshaft and maybe this is a huge issue :P

6200 rpm launch with a light flywheel vs 7000 steel launch or 4800 rpm launch control steel launch.

I would think my crankshaft being quite heavy would be part of that problem still, but I guess the flywheel has a larger moment of inertia so it throws its weight around more then the crank.
And maybe adding 10 pounds to the flywheel means I need a serious drop in launch RPM....