Anatomy of a broken Torsion Bar

[ritztoys]

@ pk2678 I have to agree with you, the area looks like rust to me. If this was dirt/rust then there must have been an extremely small fracture allowing stuff to get in and weaken the overall integrity of the bar. Didn't see any rub marks either.

The part where the failure was located is inside the fiberglass sub-body between the openings of the roof box, nothing was touching the bar!

[dmcman73]

It looks like a manufacturing defect to me. Maybe something that contaminated the steel during the process?

[dn010]

Looks the same as this one. The theory here was it was cracked at some point.
http://dmctalk.org/showthread.php?17271

[ritztoys]

@ 010 I have to agree with you on this that some kind of 'small' stress occurred during the bar's lifetime and it just finally gave up. My bar wasn't touching anything as it was completely inside of the fiberglass sub-body, approx. an inch from the base of the splines.

I figure it was just my bad luck and timing.....I had a tooth go "Belly up" too and had to have it pulled today, then next week I have to see a Dr. for a heart murmur!

At least I can still fix my car......

[Nicholas R]

That's pretty textbook for shafts failed in torsion.

There are usually 3 zones in a shaft that fails in torsion. Zone 1 is a small spot at the edge where the crack propagated from (often not even notable without magnification). Zone 2 is the fatigue zone. And Zone 3 is the torsional failure zone. The part that looks oxidized is primarily the fatigue zone with the edge being the propagation point.

The fatigue zone looks different for 2 reasons; first that there can be some oxidation if the crack existed for a while. And secondly because the failure in this zone is a due to the grain incrementally failing due to fatigue cycling, rather than a clean shear.

Zone 3 is when the rest shears cleanly all at once which is why this area looks like a clean break.

[ritztoys]

@ Nicholas R Interesting explanation, thanks for your input, always learning something new about our special cars.

I will say the 'breaking/shearing noise' was very, very loud , I thought to myself, "Who the Hell just threw a large rock at me?" I hope to not hear that again....

[Mark D]

That's pretty textbook for shafts failed in torsion.

There are usually 3 zones in a shaft that fails in torsion. Zone 1 is a small spot at the edge where the crack propagated from (often not even notable without magnification). Zone 2 is the fatigue zone. And Zone 3 is the torsional failure zone. The part that looks oxidized is primarily the fatigue zone with the edge being the propagation point.

The fatigue zone looks different for 2 reasons; first that there can be some oxidation if the crack existed for a while. And secondly because the failure in this zone is a due to the grain incrementally failing due to fatigue cycling, rather than a clean shear.

Zone 3 is when the rest shears cleanly all at once which is why this area looks like a clean break.

Found the engineer in the room

We have Torsion bar front suspensions on the trucks we build at my job. Of the failure reports I've seen, they all match what you've described. I was hoping to share some images but the reports are all marked confidential. The bars we use are just over 2" in diameter so it's much easier to see the different zones.

[ritztoys]

Well.....new torsion bar arrived, I handled it like a stick of dynamite! Routine re-assembly(not touching anything), but I found it took three tries to get correct tension.

1) Raise door so the roof section(of door) is almost vertical and install bar with locking plate/mount so far side is tilted towards you, close side touching glass glazing.(this is about 2-3 splines from horizontal)

2) Rotate bar and mounting plate to horizontal position and install bolts, then carefully check door droop.

3) Repeat procedure until door's opening is 2-4" from close. (@ elvis thanks for suggestion worked fantastic)

3a) I had to repeat this twice to get door opening proper(No Bounce either), two splines at a time.

So once again I'm very happy with my car, didn't have to contribute to the Cuss Jar either.....

@ captainneo I found about 4-6 splines from start to get proper tension as described above.

[dmcman73]

Well.....new torsion bar arrived, I handled it like a stick of dynamite! Routine re-assembly(not touching anything), but I found it took three tries to get correct tension.

1) Raise door so the roof section(of door) is almost vertical and install bar with locking plate/mount so far side is tilted towards you, close side touching glass glazing.(this is about 2-3 splines from horizontal)

2) Rotate bar and mounting plate to horizontal position and install bolts, then carefully check door droop.

3) Repeat procedure until door's opening is 2-4" from close. (@ elvis thanks for suggestion worked fantastic)

3a) I had to repeat this twice to get door opening proper(No Bounce either), two splines at a time.

So once again I'm very happy with my car, didn't have to contribute to the Cuss Jar either.....

@ captainneo I found about 4-6 splines from start to get proper tension as described above.

Awesome! Did you get a new one from dmoco?

[ritztoys]

Awesome! Did you get a new one from dmoco?

Yes I did. It's a quality product from what I see, time will tell.

I'm a retired Aircraft Mechanic.....been doing 'professional installations' for years, "Do you feel safe in your Aircraft"?..... "Why yes I do"........