Broken offset shackle bolt

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VG770

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Hi guys,

I am restoring an Australian version of the A-body.

I went to install the Mopar offset shackles. As I tightenned one of the nuts the bolt broke. Jegs claims I overtightenned which I know I didn't.

I wanted to find out if any of you had such an experience with this. I find it hard to believe that these would break given what they are designed to do.
 

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I broke one off pretty easy myself. Once the nut bottoms out when the shackle hits that shouldered part it ain't gonna take much more torque. I'm always very careful now. I think it's best to simply use some lock tight on the threads and snug it down good but don't over torque it.

Treblig
 
You can't even torque them to service manual specs. or they will break, Just snug them and they'll be ok...

I always buy an extra set of shackles when I replace them as I usually break one. Then I get the feel for when they are about to break and am able to get the others right.
 
From the picture it looks dry throughout the break. Doesn't appear to be any galling on the threads. This makes me think it broke all at once during the tightening. If a partial darkened area was there I'd say it came with a crack.
What were your torque readings and spec?
What torque wrench were you using?
Is there a shop available where you can get hardness tests?
 
They have the same problem with regular shackles too. Just snug it and be done
 
Hemioutlaw said:
Are these not grade 8 bolts?
Click to expand...

It's not the grade of the bolt that creates the problem, it's the design. What I learned about bolts and threads in the aircraft industry is that bolt threads are supposed to be designed so that when the nut is tightened there should be at least 3-4 threads still left untouched by the nut. The extra threads act as a spring that stretches as you tighten the nut. If you leave too few threads left on the bolt there is nothing to "stretch" so all the torque is quickly transferred to the last thread without any "spring" to absorb the shock of the torque. The shackle bolt threads end very abruptly at the shoulder and there is where they always break. Too few threads to stretch in the short distance between where the nut ends up and the shoulder. If fact, the number of threads that are left (that can be stretched) is basically the number of threads in the thickness of the shackle...not much. Of course it could also be the cheap Chinese cr@P!!!!

treblig
 
I did the same thing with mine. It doesn't take much to break them for sure. I replaced both of mine with stainless bolts and used nylon lock nuts just snugged up. Def did the job.
 
67dartgtgo said:
I did the same thing with mine. It doesn't take much to break them for sure. I replaced both of mine with stainless bolts and used nylon lock nuts just snugged up. Def did the job.
Click to expand...

Yep... Ny-lock and snug.
 
Treblig said:
........... Too few threads to stretch in the short distance between where the nut ends up and the shoulder. If fact, the number of threads that are left (that can be stretched) is basically the number of threads in the thickness of the shackle...not much. Of course it could also be the cheap Chinese cr@P!!!!

treblig
Click to expand...

Made in China? I would bet they don't meet the proof load spec anyway.

Evidently the nuts bottom on the shoulder. When that happens the torque will skyrocket. Too late before you realize.
 
I had it happen on a build.

Press the broken stud out
Press a stud out of a standard shackle
Replace std shackle stud in offset shackle

Do not torque so tight Godzilla
Easy peezy
 
your input is much appreciated everyone. Thank you very much. I still find it hard to believe that it would break so easy. Surely it would endure much more stress when under the load of the vehicle taking bumps and turns?
 
VG770 said:
your input is much appreciated everyone. Thank you very much. I still find it hard to believe that it would break so easy. Surely it would endure much more stress when under the load of the vehicle taking bumps and turns?
Click to expand...

I also used to think the same but as it turns out there is probably very little stress on the nut/threaded area . The majority of the load is vertical except when you turn a corner, even then the stress is spread over a large area (shackle). Then you have the rubber bushing to absorb and shock. I've never had one break once it was installed unless you over torque it and put a "crack" in the threads leaving it to break later. If you use lock tight or use a fiber locking nut you should be OK because then, even if you don't torque it down, it won't back off!!

PS - I totally agree with you about the threaded portion breaking so easy. It really shouldn't break with such little torque. The original factory shackles were probably better quality. Every time I do any spring work I always have a spare shackle...JUST IN CASE!!!
Don't forget to use plenty of silicone gel/lube (not the spray stuff) in the bushings so that you don't get that famous "squeek, squeek, squeek!!!"
treblig
 
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