Constantine

This has been a fun exercise with great input, but the real question hasn't yet been answered, can the drive shaft found by Greg and his son that was placed in backward in the 928 5-speed in question be able to be re-used without fear of failure in the future.

The drive shaft has already been used wrong way round in the 928 for unknown years and mileage with seemingly no ill effects and no signs of damage. So it would seem the drive shaft will most likely survive if placed back in correctly. But is it worth it since it seems it has led a somewhat abnormal life at this point? That question should be answered by the owner who has a choice of popping for a new drive shaft or not.

Any decision on this yet, Greg?

Darklands

I don´t know how much Gregs driveshaft costs but one day labour if the old shaft fails is three times the money as if you replace the shaft.
So I would do it the safe way.

Constantine

Agreed.

It won't be just a drive shaft replacement in the future, but another torque tube rebuild, drive shaft and labor.

icsamerica

There is only one way to know for sure. Leave it in backward and test it in the real world. A vigourous track day or two or three will provide the answer. I'd wager it will be fine and something else unforeseen would fail first.

https://iopscience.iop.org/article/1...3/1/012015/pdf
I found some formulas on page 2 of this document that seem to apply.

Mathematical analysis is good and but I often find myself saying... "this is why we test".

Subaru is very good this, One look under a WRX and I find myself saying, there just isn't enough metal here but they work fine IRL.

Constantine

Understand the proclivity to test such a scenario as given here, but as anyone involved in testing such things would know, this is not anywhere near what would be needed to answer Greg's question.

Bottom line, if this was your 928, what would you do?

GregBBRD

Truthfully, the torque tube shaft, in this car, is not the biggest issue. The engine has a bunch of grief and will require a lengthy "stay" at the "machine shop hospital" for repairs.
Once I get the torque tube out of the car, I'll get to see both ends and judge the damage, if any.
Currently, the car has been moved off the lift, had the hood put back on, got washed, and covered.

In the interim, I've got this extra sock and short chunk of twisted aluminun wire I've been carrying around all day, twisting both n the clockwise direction, turning them around and then twisting them in the clockwise direction, again, only to find out they don't untwist.

In what soared time I have, I've been drafting my resignation letter to Space X, just in case.

It's no wonder all those rockets I worked on all fell over, when they landed back on the pad.

I thought they were all rotating the wrong direction and I was firing the incorrect compensation rockets to contol the spin!

Darklands

If you pull the plug from your bathtub you can see the coriolis force! I think it´s also a problem in rocket science!

Gage

Greg, I can recommend Twizzlers as a follow up testing and support medium. If you start to relapse and are having torsional doubts, pull one from the bag, run a quick test, then enjoy a tasty licorice treat.

GregBBRD

My last post had just a twinge of sarcasm in it.
I actually got a promotion, from Space X, for understanding what is occurring to the shaft....

It's pretty obvious that anyone still confused by what is occurring, has not tried my proof of concept, spelled out in post #30.

Simply do this "experiment" and look at what is happening to the shaft, from the point of view of the ends of the shaft.

Jerry Feather

What is spelled out in post 30 involves a semantics problem. When you look at the engine/driven end it is turning clockwise and twisting clockwise. At the other end it is turning counter clockwise and twisting clockwise. When you swap ends it is doing the same thing. Twisting and turning have different meanings. Period.

GregBBRD

OK.
Well, let me be clear:
I don't give a cr@p what direction the shaft is turning. It is clockwise. And when it gets turned around, it is still clockwise, because that is the direction the engine turns it. (Let's call that a "given".)
I'm only concerned about the twisting of the shaft.
And when it gets turned around, end for end, the twisting is in the opposite direction. Period.
Which could potentially lead to shaft failure.
That is my concern.

Jerry Feather

That's fine Greg, but that is simply wrong.

Instigator56

I thought Post #37 showed that the twisting of the shaft is not in the opposite direction. What did I miss?

icsamerica

So I guess U-turns are out then.

Ed Scherer

Nothing. It's compelling and easily repeatable. Hell, throw a piece of stranded wire in a drill, twist it up a little more (holding the other end as "the load"), then switch ends and try some more. Does it unwind? Nope. Perfect analogy for the torsional stress on a shaft.

No, it isn't. Exclamation point! (bolded written-out punctuation adds authority! )