Do Torsion bars just break?

Took my big block 68 barracuda for a quick shakedown run around the block. Its a big block 4 speed car now. Car was fine.

Brought it back and parked it.

Next morning came out and the driver front was sitting on the ground. Started to inspect what was causing this, the t-bar, about 4" back front the lower control arm busted. Snapped.

No visable damge to the bar, just broke. Weird, lucky I wasn't driving when it let go.


Now I have to replace them. I belive these were orginal 1968 /-6 bars. Now I am looking for a recocmendartion on what bars to put in there. This is a street car, but I plan on tracking it as much as I can.

Yes, on a rare occasion they can just snap. My Dad was at a family reunion 50 years ago and a relative was showing off his new Plymouth. As if on cue, one of the torsion bars snapped as they were looking over the car. Rare, but it can happen.

I've seen several that were broken in wrecked cars at the junkyard. They have always been the small slant six bars.
Originals in a race car with a big block ??? I'm amazed that they didn't break sooner.

Yep, they'll snap like that once a crack goes most of the way thru. The crack usually starts with a small scratch or chip and then spreads across the bar over a period of time.

/6 A body bars shouldn't be too hard to find. I think I have a set sitting on the shelf out in the shop.

Never seen a Mopar torsion bar break myself. But I replaced more than a few in Chevy trucks that snapped.
Doug

Every mechanic that did his apprenticeship between 1957 and about 1962 had at least one of those in his toolbox for a pry bar. They broke close to the end at a fairly shallow angle so they were ready made for the job.

Kevin

on my 71 plymouth sat. drove to the track full night of racing drove home and same thing came the next day and it was snapped

had one break in the pits after racing . swapped wheels , packed the boot just about ready to leave just siiting there . BANG .

Tex

I've never experienced a torsion bar break on my cars but Dad had 2. One on his 57 Hemi Desoto and one on his 66 383 Satellite. Both situations over night. Found when heading out to go to work the next morning.

when they first came out in '57 they'd break. i remember my dad pulling out of the driveway and heard a loud crack; bar broke. i don't know when that type of issue was solved but haven't experienced a break. i wonder if todays breakage may be related to offshore materials and manufacturing?

I worked on Mopar police cars for years starting in the 70's. It was in the colder climate of Ct. at the time. They used a lot of salt on the roads during the winter. The salt etched the torsion bars, especially the bent bars of the F body cars of the 80's. Quite a few times walking out to the patrol lot in the cold mornings you would see cars leaning to the side with broken T bars. This was due to the salt getting into the rubber support bushings, etching the bar and causing it to snap. Bill

Back in the late 90's a customer came into the shop during the winter and said he had a frozen shock. He parked his F150 on uneven ground the night before with the RF on a hill. Now the RF was on the bump stop. We drove the truck into the shop and found a broken torsion bar. The next morning the entire front end was on the ground. Over night the LF bar snapped too.

Dads 58 Plymouth station wagon had one break going over a slight rise then down into a depression in the road going about 25 mph. Dealer in town fixed it. That was around 60-61

FF makes them for the OP needing a new set.

http://www.firmfeel.com/default.html

.

I think your original, still unanswered, question was, "do TB's just break?".
I have zero experience with that outcome, but what I have read here for nearly 20 years, the answer is yes, they just break anecdotally when parked, most of the time.
Why, I have no idea, but am very curious. The explanations above do not address, IMO, why its most often when parked.
It might be the ones that broke at speed, put the driver in the cemetery, and we never heard the real reason why they crashed?

Chevy dealer I worked at sold a new Blaser and a torsion bar broke on the freeway so the dealer bought it back and installed a new one. It was resold as "new" and it broke again a second time months later under the 2nd new owner. The dealer bought it back again from the 2nd guy when they realized there was something wrong with it. It sat on the lot for a little bit and then a GM regional rep showed up, looked at it, and then scheduled it to be hauled away someplace. Not sure what happened after that. Could have been put together with an alignment issue and something was in a bind that was making the bar break? Who knows...

Classic torsional fatigue fracture with the spiral break at a 45 degree angle. Happens to people a lot too, especially in their leg bones.

Jcc, I don't pretend to be an engineer. I do know I can be long winded at times so I neglected to mention more of the issues which leaves some things unanswered still. Some of the broken bars I saw had rust or corroded spots in an area of the edge of the crack, suggesting to me that is where the crack initiated.Cracks in steel and fiberglass generally don't stop travelling unless drilled at ends and welded or stitched. This obviously won't work on spring steel. After we drive the vehicle and the engine is warm, we shut it down and all the materials cool and contract,accelerating the cracking process when parked over night. I think this is along the same scenario as why we are told not to rev up cold aluminum rod motors (besides bearing clearance issue). Most of these older Tbars being talked about, I'm sure have at least spotted rust areas over time. I guess what I'm inclinded to believe is that this breakage doesn't just happen all at once. In Connecticut with winter salt, this was the issue with Mopar police cars. I then moved to Florida to work on police cars, not one broken torsion bar in 28yrs. Has to be something to it.In Ct. our fleet parts dept. had to keep torsion bars in stock. That doesn't seem right. Bill

Yes, I agree that the failure process occurs overtime, exempting a hard crash, be it corrosion, fatigue, notch sensitivity, etc and/or some combination.
What catches my attention, is the final chapter of that failure process according to years of reports here, often occurs suddenly, and at rest, which I find hard to explain.
The cool down heat gradient idea is interesting.

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."