Torsion Bar

[mluder]

How common is this? It's a scary thought.

Not common at all... The torsion bard were tested to over a million cycles or some wild number like that. I just happened to be lucky.
There are a few precautions you can take. Visually inspect your bars regularly for nicks or scratches - That's typically why they fail.
Make sure the rear door hinge is not rubbing on the bar - this is a common source for the above mentioned scratches/nicks. You should be able to fit a playing card or similar between.
There's also a procedure for cleaning off surface rust. I don't know it off the top of my head so I won't even try to guess. It's here on the forum somewhere. Perhaps some one with a better memory can point you to it if a search doesn't turn it up.

All that said, your mileage may very and you could do all of this and it will still snap tomorrow. Like I said it's rare but does happen.

Cheers
Steven

[Rich]

There are a few precautions you can take. Visually inspect your bars regularly for nicks or scratches - That's typically why they fail.
Make sure the rear door hinge is not rubbing on the bar - this is a common source for the above mentioned scratches/nicks. You should be able to fit a playing card or similar between.

+1 on this.

In case an inspection turns up a torsion bar touching the rear hinge a simple remedy is to slip a short length of strong hose or tubing over the bar to cushion it against the hinge. Slit is lengthwise to get it over the bar and orient the slit anywhere but facing the hinge. The bar may bend a bit with the hose there but that won't cause a problem.

Manufacturing variations mean that some bars hit the hinge and some don't. Don't take chances, just prevent any nicks.

PS, the OP on this thread could perhaps tell us at which location their particular torsion bar failed - if not reported already here. Anywhere near the rear hinge?

[Dangermouse]

All the ones I've seen are at the rear of the bar, presumably where the stresses are greatest near the fixed part of the bar.

Just personal theory on this, but I think in the cases where the roof box is starting to separate, that allows the bar to come in contact with the rear hinge and gets a little nick in the bar which acts as a stress crack. I don't think minor surface rust will affect the integrity of the bar, but it may hide a nick.

[papanoel]

+1 on this.

In case an inspection turns up a torsion bar touching the rear hinge a simple remedy is to slip a short length of strong hose or tubing over the bar to cushion it against the hinge. Slit is lengthwise to get it over the bar and orient the slit anywhere but facing the hinge. The bar may bend a bit with the hose there but that won't cause a problem.

Manufacturing variations mean that some bars hit the hinge and some don't. Don't take chances, just prevent any nicks.

PS, the OP on this thread could perhaps tell us at which location their particular torsion bar failed - if not reported already here. Anywhere near the rear hinge?

my car has a zip tie in that spot to prevent rubbing.

[David T]

my car has a zip tie in that spot to prevent rubbing.

All the ones I have ever seen break where they pass by the rear hinge. My guess is that they rub it and get scratched creating a stress riser where it finally breaks. I just take a piece of rubber from an old inner tube about 1" by 2" and pull the bar away and stick it in between the bar and the hinge.

[opethmike]

Kind of like has already been mentioned several times, eh Guru?

[Patrick C]

Cinching a plastic zip tie around the bar where is nears the rear hinge is the best preventative fix for the bar rubbing the hinge. It works well and looks better than an old piece of rubber scrap.

[mluder]

Interestingly (or maybe not) mine broke near the front of the car. Hard to tell if there was a nick or not as when it breaks it essentially shatters and pieces chip off.

It's the most sickening sound. I had arrived at the gym. Parked, closed the door and as I was walking away heard a loud pop. I knew right away what it was. Got back in to the car and immediately went home. Exercise motivation deleted.

Cheers
Steven

[Delorean3610]

Interestingly (or maybe not) mine broke near the front of the car. Hard to tell if there was a nick or not as when it breaks it essentially shatters and pieces chip off.

It's the most sickening sound. I had arrived at the gym. Parked, closed the door and as I was walking away heard a loud pop. I knew right away what it was. Got back in to the car and immediately went home. Exercise motivation deleted.

Cheers
Steven

You could have done a few sets of door lifts at home anyway.

[Rich]

All the ones I've seen are at the rear of the bar, presumably where the stresses are greatest near the fixed part of the bar.

Just personal theory on this, but I think in the cases where the roof box is starting to separate, that allows the bar to come in contact with the rear hinge and gets a little nick in the bar which acts as a stress crack. I don't think minor surface rust will affect the integrity of the bar, but it may hide a nick.

It turns out the stresses along a circular bar of constant diameter are equal from one end to the other, assuming the torsion loads are only at the ends, as in this application.

Yes, a nick or scratch that's deep enough can create the stress concentration that can eventually lead to a failure at or near the point of the defect.