Broken drive shaft

[blsfrs]

Originally Posted by Sapphireho

Looks like a two piece shaft to me!?

It certainly is 2 piece now.

[Turdinator]

Why bolts when all the damage is in the middle? Not saying anyone is wrong, just trying to learn something.

[Ultramaroon]

Originally Posted by Turdinator

Why bolts when all the damage is in the middle? Not saying anyone is wrong, just trying to learn something.

Once the rear u-joint loosened enough for it to spin off axis, it was doomed. Still being fastened at both ends, it buckled like a bent straw. It looks like it may also have gotten scored rubbing against maybe the exhaust. Once a crack started, torque quickly finished the job.

Whole lotta guesswork based on those pics.

[blsfrs]

Originally Posted by Ultramaroon

Once the rear u-joint loosened enough for it to spin off axis, it was doomed. Still being fastened at both ends, it buckled like a bent straw. It looks like it may also have gotten scored rubbing against maybe the exhaust. Once a crack started, torque quickly finished the job.

Whole lotta guesswork based on those pics.

I can agree with the off axis rotation causing stress but there was absolutely no vibration. No rubbing noise either. Scoring most likely happened when the broken ends dropped on to the dyno frame.

[Ashikabi]

Originally Posted by blsfrs

I can agree with the off axis rotation causing stress but there was absolutely no vibration. No rubbing noise either. Scoring most likely happened when the broken ends dropped on to the dyno frame.

No vibration you were aware of. If spinning on the Dyno it's conceivable that it started vibrating and then failed completely in such a short amount of time you didn't even notice. That aluminum tube is strong when twisted perfectly on is axis but start bending it(with centrifugal force) and it will fail very quickly. Drive shaft is spinning very quickly

Sent from my ONEPLUS A5010 using Tapatalk

[Ultramaroon]

Originally Posted by blsfrs

I can agree with the off axis rotation causing stress but there was absolutely no vibration. No rubbing noise either. Scoring most likely happened when the broken ends dropped on to the dyno frame.

Yeah. It's a head-scratcher but, like Ash said, it all happens in a blink of an eye. I see your point about the scoring. I'd have to get up close, maybe even with a loupe to really examine it.

Shit breaks. Super lucky it was on the dyno.

[Grady]

Close up pictures of the fracture could give us a clue if a crack progressed into a failure or it just failed. Plus you need to look at the scoring at the failure point. It almost looks like the scoring came before the failure.

[Ultramaroon]

Originally Posted by Grady

It almost looks like the scoring came before the failure.

Yup. Chicken <-> Egg

[Jdmjunkie]

I am glad it didn't happen on the street, this just reinforces my notion of putting a safety loop when going to an aftermarket one piece drive shaft.

[Grady]

Originally Posted by Ultramaroon

Yup. Chicken <-> Egg

Yep without close examination it is all a guess. And even then it may not be conclusive. Now get to the microscope level we could figure it out.

[EAGLE5]

Originally Posted by FrickingReallySlow

Subaru notes these as one time use items but I never understood why, if its not rusty/striped what's the mechanical reason they can't be reused?

Many bolts are designed to deform in specific ways when tightened. If they're pulled out and then put back in, they no longer meet the spec and can have issues. Tesla recently had a recall over this, with factory workers torqueing, loosening, then retorquing. The bolts needed to be taken completely out, replaced, and torqued properly ONCE.

[NoHaveMSG]

I've probably pulled and reused the driveshaft bolts about 6 times on my car Always German torque. I should probably buy a crows foot and do it proper.

Edit: Now that I think about it a bit harder, it is probably more like 12 times.

[FrickingReallySlow]

Turning it 4 times to try to get rid of vibration is def PITA having to get new bolts each time. But also there were a couple of threads a while back about the bolts being too short with aftermarket shafts and results in only half your nuts thread engaging. Solution was to get longer bolts so that all threads engage. I still haven't done it yet on mine @blsfrs do you remember if all the threads engaged on yours?

[EAGLE5]

Originally Posted by NoHaveMSG

I've probably pulled and reused the driveshaft bolts about 6 times on my car Always German torque. I should probably buy a crows foot and do it proper.

Edit: Now that I think about it a bit harder, it is probably more like 12 times.

It's probably gonna be fine 999/1000 times in the first year.
But that 1/1000 is bad enough for a safety recall. 1/1000 * 100,000 cars is 100 failed cars that could kill people in the first year. And then the car companies look at a car's life over 20-30 years, and they start to sweat, because that 100 failures can become 10,000 or more if things go badly. Hence we get our valve springs recalled.

But you? In a car you probably inspect often? Fuggetaboutit.