What Grade Bolts For Roll Cage?

Josie'sLandCruiser

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Hi All:

As part of finishing-up of the body tub swap on my '74 FJ40 I'm installing a full roll cage, and will be using 3/8ths inch bolts.

I've heard that Grade 5 fasteners will streech before failing, while Grade 8 bolts, though "stronger," are also more brittle. Don't know how much truth there is to any of this.

Opinions from those of you "in the know" regarding which grade of bolts to use?

Thanks in advance!

Regards,

Alan
Seattle
 

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Oh...Durka Durka Durka.
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Are you installing backing plates below the body, or is this cage frame mounted?



I only use grade 8 Caterpillar fasteners to mount the cages that I install, through 1/4" backing plates that are of a larger size/shape than the piece that it attaches to on the top side of the body, weather it is frame mounted or not.




But again, that is just me. There are many ways to do things. To each their own.


Good luck!


-Steve
 
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while grade 5 bolts will "stretch" more before breaking, they will stretch and then break under less stress than a grade 8 bolt... so a grade 5 bolt will stretch and break before a grade 8 bolt will be anywhere near stretching too far... given equal loads applied in the same way.
 
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Hijack!

How does Grade 8 weld? Any fumes like galvanized? I have just about finished the frame mounts for the roll cage and want to weld some nuts on the bottom of the plates.
 
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They weld fine. The zinc chromate shouldn't be breathed as it is toxic. The downside to welding grade 8 nuts or bolts is that the strength rating will likely decrease due to internal stresses in the metal from the welding process.
 
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shear strength on grade 8 bolt with 3 threads is only 2800lbs .psi is hard to calculate as the diameter is less than an inch.grade 8 bolts have a lot of stretch as well grade 8 3/8" bolts for roll cage is about as minimal as you should go. just my opinion
 

Morse_FJ40

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Alan,

I hope the cage works for you! I would add a plate to the underside of the tub for the cage to bolt to. I just pulled the top and doors off my cruiser, so I can go park it at my dad's so I can plasma cut my gas door and filler ass. to put into to my new tub. My new tub is all welded up, and blasted top to bottom and ready for the POR-15.

later
Ryan
 

dgangle

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too tall said:
shear strength on grade 8 bolt with 3 threads is only 2800lbs .psi is hard to calculate as the diameter is less than an inch.grade 8 bolts have a lot of stretch as well grade 8 3/8" bolts for roll cage is about as minimal as you should go. just my opinion
What is your source for the 3 thread info? I never heard of such a thing. Area of a 3/8" bolt is A=pi(r^2) or 0.589in2. Simple calc but I am curious to the 2800 psi thing.
 

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tonkota said:
Only 'cause he likes things yellow (snow?) ;)

Not really.


I was at Morton Illinois, Caterpillar’s main parts distribution facility a few years back, and got to do some destructive testing to hard wear that they were receiving in. I put a 1” grade eight fastener into a machine that tries to pull the head off. That did not happen, nor did the threaded area fail, but the shank, above the threaded area is where it broke, (where it is designed to fail) at 180,000 PSI, well beyond its rated limit. It was very entertaining, as there was a tour group in there that had no idea that when this bolt failed, it was going to sound like a bomb went off, and when it did let go, a couple people screamed, and then started to weep. This was pre September 11 too, as I was able to carry the broken fastener onto the aircraft on my return flight. The security people at the screening counter enjoyed the story, and thought the bolt looked pretty cool to. Nice and sharp! There is no way that would be allowed as carry on today. I will dig it out when I get back to the shop next week, and try and get a couple pictures of it.


Good luck!


-Steve
 
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