Anatomy of a broken Torsion Bar

[ritztoys]

I thought I'd share pictures of the broken pieces of my Driver's Torsion Bar. It appears that there might have been some surface problem that ultimately led to it's failure.

(it cleared the hinge too, notice the rust!)

64399 64400

What's interesting for me I installed this over 25 years ago and made sure it would not rub on anything, once fully bolted in position.

[Rich]

Interesting.

There's some kind of surface irregularity at or near the fracture, as you say.

Was this bar NOS when you installed it 25yrs ago or did it come off of a donor car? It might have been compromised.

[ritztoys]

@ Rich This was NOS back in the day.....don't remember who I purchased this from. My 'D' records are buried in the garage somewhere. :hmm:

[captainneo]

when putting these in, how many notches do you end up turning? roughly?

[ritztoys]

@ captainneo With the new bar coming in on Friday, I'll be starting over on "pre" torquing the new bar. The method is to pre torque the Torsion Bar so it holds open

the door approx. 4-6" from full close, without the gas cylinder assist.(it is completely removed during the re-assemble of the Torsion bar)

Since I do this by myself, I usually use a long "cheater bar" connected to the hex socket , which sets on my shoulder while installing the bolts into the

locking/mounting plate for the splines.

[Elvis]

That's 2-4 inches too much AFAIK

[ritztoys]

@ Elvis Thanks, I'll use your measurement suggestion when I'm setting my Torsion Bar. I'll check it against my passenger door.(still original Bar)

[cdrusn]

Since you are doing the drivers door then you must be getting your new bar from DMOCO. I installed one of their bars a year ago and within two months it snapped. They
would not honor the warranty because I installed it myself. They explicitly list professional installation required and they should also say it voids warranty if not done. They wouldn't even give me some credit for another one. Since as far as I know they are the only vendors I paid full price for a second one. They do not manufacture the torsion
bar. It is made by a supplier to them who also supplies Delorean Go. Good luck! :bigcry:

[ritztoys]

@ cdrusn I sent you a PM, can you maybe explain what these folks mean "professionally installed" ?

[pk2678]

2/3rd of the fracture surface looks silver. 1/3rd looks black. Is that the rust that you mentioned? If it is rust or dirt, it must have been there for quite a while.

Peter

[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......:rolleyes1:

[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 :shock:, 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 :aniclap:

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.....:woot:

@ 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.....:woot:

@ 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"........