YIKES! Carbon fiber driveshaft goes bang...
 

An expensive weekend on the dirt.
Very suddenly let go, (luckily) on the entry to a moderately slow "chicane".
Initially thought it might have been due to a rock strike, but where it fractured is well protected by a large exhaust mid mount muffler (I think the vulnerabilty to impacts would be much further along the shaft closer to the diff).
It was fitted about 2 years ago so I'm not really sure how to properly or realistically diagnose the failure.

Which brand is it?

Driveshaft shop.
(NB not from Verus, as I previously wrote)

heat soak failure from the muffler?

Yeah, I guess thats very possible too.

In truth I'm not sure what the temps are like there, although it has never really struck me as a super hot zone, and I have some home made rubber exhaust hangers there that seem to have coped well over time.

But you make a good point.

Excessive pinion angle?

with the rear diff being fixed, unlikely. pinion angle really has more issues at extreme axles in solid axle, extended travel builds.

i don't know what he's got for mounts/bushings on the diff or engine/trans, but anything oem or even if if he's got all poly, should not cause any extreme issues to the drive shaft. unless there were a failed bushing that allowed either assembly to get clocked off center.

Well that sucks, especially now since getting a replacement is going to difficult to impossible. You could probably do some hardness testing just outside of the damage and compare it to then end at the diff ti see if it was heat. My initial guess would be it got damaged in that area then failed.

I'd consider reaching out to Verus to see what their thoughts are. That sucks, sorry to see

CF imho is very light & strong, but brittle material, no? Where metal would bend a bit, it shatters. And rally use over rocky roads .. there might be numerous hits over this through 2 years of rallying .. and might be from long time ago and eg. developing small crack, which ended up with failure at this race. My choice probably would be for rally use, maybe one piece, but more conventional material choice of metal. Unless whole underside is completely guarded by extra protection pans, including tunnel where shaft runs (may cause overheating issues due closed off with reduced venting exhaust in same tunnel though)

^^^this


How much design factor to account for scratches/divots? Stress risers lower actual critical speed.

Also interesting but might be coincidental, the failure occurred approximately where the stock driveshaft is divided.

Any pictures of this? (assuming this is a custom setup)

Yes that was the initial thought at the time by everybody, but we all became less sure that it may have been the (only) factor when we removed the shaft.

I'm confident that it hasnt had a "big" rock strike in that particular area (and even the more exposed portion closer to the diff is in very good condition).

The area surrounding the failure is quite well protected.

However of course I cant rule out some sort of impact at some point.

I have refitted the alloy driveshaft that it replaced.

An engineer who helped me with the car afterwards made a similar point about the location of the fracture along the shaft, saying it was at/near the shafts maximum stress point (or words to that effect),

Our first reaction was some simple sort of impact fracture (at some point), but our gut feeling is that there may be some other factors at play.

Somewhat counterintuitive is the overall condition of the carbon, which is almost completely umarked (to the eye) along its length. * aside from the large scrapes and marks which correlate to hits taken as it spun free of the gearbox, and then being towed off the track.

Of course having said all that, it was always a risk running carbon on this car!