If you look at broken torsion bar you can see how the fatigue crack grew across the bar. If you have high power microscope you can even count the number of cycles that the bar went thru before it broke. It is typically a very high number, maybe 100,000 cycles so it could take years for the bar to crack all the way.

A TB that 100,000? cycles lifespan for a final failure must be way over designed for the task, in that with the increasing stress concentration of a continuously growing crack, combined with the decreasing load bearing cross section area in play, means the bar has to be way over designed to endure the expanding crack until the final failure. I am not sure how much safety factor is built in intentionally to delay final crack initiated failures, which once begun, must be the final outcome.

I replaced both of mine after I had to adjust one of them three times in less than a month. I didn't wait for it to break. It didn't break my heart to send a highly stressed fifty year old part to the scrap yard. The new bars haven't needed any adjustments since I put them in several years ago.

back in the mid to late 80's, my brother had a 73 or 74 dart sport [sunroof car-he hated that option. not sure why, it didn't leak].
he was going down a back street [35mph, possibly] and the passenger's side bar broke. just a "pop", and the car dropped. he thought he had a flat until he got out and looked.
a different [new to the car] bar and all was well with the world.
it was a break like Andy showed.
our area is a salt zone, so that's what we blamed it on.

They do, but they cost a ton of money. I'll sell the used /6 bars I have for $40 if the OP wants them. Shipping will probably double that to $80 total but still will be a lot cheaper then new prices. Local CL might find some torsion bars, it is hit or miss around here for used torsion bars.

I'm currently building a custom set, B length, C Hex, CM 1.37"d hollow, approx 500ft/lbs, farmed out, IMO would be very costly.

P-S-T makes new t-bars at reasonable prices, that's where I got my 1.03" A-body bars. They also give a discount to FABO members, possibly for other forum members too

First Mopar I ever owned was a 70 Charger R/T I bought in 77. One day I was pulling into the car wash lot where I worked (very mild incline) and I heard a loud snapping sound and my front end dropped on the passenger side. Took it to an auto repair shop and they told me the torsion bar broke. I had it repaired and believe it or not the driver side bar broke about a week later. I didn't make much money then so having taken it in to a shop to have it repaired twice in such a short period of time wiped me out. Never even heard of a torsion bar until that happened as I had owned Chevies up till then.

Thanks for the offer. I just purchased a set of slightly thicker bars from "sway away".
I hope they come soon, they claim to have several in stock.

I wrote a tech article on torsion bars for Mopar Action a number of years backed and listed some calculations that showed how much stress the /6 bars are under in a car. Using /6 bars in a B body is just asking for trouble since the bars are under so much stress. A small knick or gouge on a /6 bar in a B body car is enough to start a crack. The bigger bars are way less likely to snap since they are under a lot less stress. Bars bigger than the factory Hemi bars probably never snap unless get damaged really bad.

Can someone please share the list of torsion bar numbers? I know they should be paired and how to tell right from left?
Even and odd part numbers even = right, odd = left ? Thanks in advance
Copper

Anyone using a 50 year old six cylinder TB is asking for trouble!

Seen lots of big block A Bodies running Six Cylinder TB’s for drag racing?
They are supposed to give better weight transfer...

Anything that keeps the car off the ground, tyres, TB’s leaf springs and shocks are Mega important.

Never seen a broken TB myself but a lower ball joint failure on my Charger R/T, certainly gave me fright...

Not to hijack the thread but since we're on the subject of torsion bars, when installing them is there a specific way they are supposed to go in? I heard once they had to be "clocked" but never found out if that was true and if it was, exactly how are they supposed to be "clocked"?

Factory torsion bars are clocked 30 degrees against the twist. So they have a pre-set against the twisting force of holding up the car. That is why they need to be installed on the correct side. If you install them on the wrong side (hard to do) then you defeat the pre-set.

Aftermarket bars can be a crap shoot. There have been aftermarket mfgs who didn't understand the pre-set and they didn't properly clock their bars. If the bars are not properly clocked then the you'll have problems getting the car to sit at the correct ride height. I think most of those issues have been resolved but it was a big problem when Mopar first started jacking up the prices on bars and people started trying to make their own.

my ro23 belvedere, in ss/ea, has to weigh 3770 #'s, i had /6 tbars in her forever, then several months ago, on a Thursday, had to download some info from the tach. came back Monday opened garage door & car was sitting on drivers tire. remember this is a big wheelstanding heavy car, so I thought its life cycle had ended. just so happened I went to my chassis guy, for another problem, & just wanted to show him the bar & ask if this was a stress fracture, it broke in a 45* curl with a raised line on one side & a depression line on the other. he said you know how that happened? a welding arc. i looked closer & yup you could see where the arc had punctured/popped a tiny hole thru the paint & outer surface of the metal. guess over time the fracture just cut it's way across. nobody in the household ever heard the bar break. i could just imagine what would've happened if it broke going down track at speed. i have a picture of it but don't know how to post it. replaced the bars with another set of b body /6 bars & she's wheelstanding again. Dave #1355 ss/ea

I thought these quotes from well known racing guru/author Carroll Smith are pertinent here, from his 1990 book "Nuts, Bolts, Fasteners and Plumbing Handbook", pages 26 &27:

Regarding Fatigue:

"The initial crack has reduced the cross-sectional area of the member. Consequently there is less material available to resist the next load cycle. We know that unit stress is load divided by cross-sectional area. Therefore, the next time the load is applied, the imposed unit stress will be greater than it was the last time (assuming an equal load). More important, despite the migrated dislocations, the jagged bottom of the initial crack acts like a first class stress concentrator. Just as wolves always go after the weakest member of the herd, as more load cycles are applied, the concentration of stress at the leading edge of the crack will cause the crack to enlarge until enough fresh material is engaged to resist the stress, this time. These fatique cracks are transgranular in nature; the fracture actually splits the individual grains of the metal rather than following grain boundaries. As a result, the opposing surfaces of the crack tend to be quite smooth in appearance."

"This repeated sequence of events creates typical smooth opposing surfaces with the telltale concentric beach marks that are also visible in the illustration. The beach marks are formed by the progressive enlargement of the crack and radiate outward from the focus of the original fault. Beach marks are characteristic of the fatique failure...…… The next sufficiently large load application sudden and catastrophic failure of the remaining portion of the metal. This last failure is intergranular in nature."

"The final rupture proceeds along the grain boundaries, leaving the individual crystals exposed as a rough and granular surface. This allows the self appointed expert to peer knowingly at the part and proclaim, "Ha! Just as I suspected, a crystallization failure" . When you hear this sort of statement, the proclaiming person from your list of those to be consulted in the future."

"it is important to realize that, in the fatique history of any part, neither the rate at which stress is built up within the part nor the period of the time over which the stress is maintained is significant."