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What size bolt...

Discussion in 'The Garage' started by pvfjr, May 1, 2005.

  1. pvfjr

    pvfjr 1/2 ton status

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    Time to play that game again. What size is the bolt for the front bushing and hanger of the front leaf spring? I would match my old ones....but I think they're wrong! Need diameter and length. Would grade 5 or 8 be better? I know 8 is supposed to be stronger, but is also brittle. Bent's better than busted, but I don't know.
     
  2. readymix

    readymix 3/4 ton status

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    Grade 8 all the way. And no it is not more brittle. Just look at the tensile strength. Of course people think that G8 is brittle and bent is better than broke but it is a myth that does not hold water at all.

    As for the size, i think mine were 9/16. not sure of the pitch though. I would go with a fine pitch if you can get them.
     
  3. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    9/16", course thread, 5" long, SAE grade 8.

    8 is ALWAYS better than 5. The old "its brittle it'll break" thing is a myth. Definitely not true. The gr 8 bolt is stronger is every way. I wouldn't recommend using grade 5 bolts in anything suspension related. Your life is literally resting on those few bolts.

    j
     
  4. pvfjr

    pvfjr 1/2 ton status

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    Alrighty then, thanks. It's off to home depot.
     
  5. az-k5

    az-k5 1/2 ton status

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    The myth is just that, a myth. A G5 will bend, and a G8 will shear. That is the only fact to the myth. The real info to be had is that a G5 will bend, snap, and fail, long before a G8 will even flinch. However, if loaded incorrectly (open gap in shear) a G8 can bend too.

    Some believe fine thread is better cause the nut will have to rotate many more times to actually loosen up. I run coarse thread on all of them with steel lock nuts.
     
  6. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    fine threaded bolts also have a larger minor diameter, which could be another benefit. When I replaced my leaf spring bolts recently, I went with 1/2" longer coarse thread bolts so they wouldn't be loaded on the threads like they are from the factory. Im not an engineer, I don't know if it makes much of a difference... but loading a bolt in shear on its threads doesn't seem like the best of ideas.

    j
     
  7. Cmoe

    Cmoe 1/2 ton status

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    quality of the bolts are determened by where you buy them! I buy my bolts for the suspension at a bolt company, like Canyon State Bolts.. We tested bolts from a couple of hardware stores and from a specialty store and the shear point was way different, along with hardnest.
     
  8. ntsqd

    ntsqd 1/2 ton status

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    Bolts loaded in Shear should never have any of the shear plane(s) in the threads. It is perfectly acceptable to stack a few washers so that the shear loads are carried only on the shoulder of the bolt.

    IMHO a G8 is too brittle for a spring eye bolt. Given the option I would use a LARGER G5 than a smaller G8. The other problem with G8's (no fault of their own) is that very poor quality overseas produced bolts have been coming into the country. These bolts do NOT meet the G8 specs, but are marked as being a G8. Even the gumberment, for all of their documentation requirements, has had problems with cheep bolts leaking into the supply system.

    When it's a critical bolt and going larger isn't possible I prefer to use a SHCS ("Allen") bolt. They are stronger AND more Ductile (opposite of brittle) than a G8. The tensile strength spec for a G8 is 150,000 psi. Same spec for a SHCS is 180,000 psi. Note that the other socket head bolts (Buttons, low, and flats) do NOT have the same spec, theirs is lower than a G8.
     
  9. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    i agree that bigger is almost always better... but I'm not sure most of us need a bolt larger than 9/16" for leaf springs. I mean, the single shear strength of that bolt is like 37,000 pounds or something... and they are all loaded in doubler shear. yikes! Im not a hardware expert, but when I did my 52" spring swap I did use 1/2" longer than stock bolts to get the shear connection off of the threads. I keep the stockers around for trail spares "just in case", but otherwise I wouldn't run them.

    j
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    GM originals...

    All the GM 4x4's I've taken springs off that were stock unmolested trucks had grade 5 bolts in the spring shackles and brackets factory(3 lines on the bolt heads)....I did use grade 8 bolts to reassemble them,never had any troubles--cant be any worse than the rusted pitted bolts I took out!...I see many GM 4x4's with lift kits people put in with 1/2 inch bolts instead of the correct (and harder to find) 9/16 bolts that belong there--and they wonder why the truck wanders all over the road!

    I agree about the cheap china bolts that are flooding the market--its getting hard to find quality stuff anymore--and the prices are getting crazy too--a 1 inch x 6 inch grade 8 bolt for my crane on my flatbed was $6.50 at Lowes,and it had a "hencho en mexico" sticker on it!--I dont trust it any more than the hunk of old riding mower axle I had stuffed in it temporarily(and lifted some pretty heavy loads with!)..I'm going to find a peice of cold rolled 1 inch stock to put in there instead...I dont like the thoughts of an engine crashing down on me while I'm loading it into my truck bed...

    While on the subject of cheap bolts,A friend had a IHC Scout,one of the old ones (1963)--he broke his u-bolts while beating it on a sunday at a local sand pit--no parts stores were open,but we tried a local hardware store,we were desparate to find ANYTHING to get the truck out of the pits before we got in trouble--all we could find for "U" bolts were thin things about 3/8 like muffler clamps--too short and too thin--in desparation,we bought the largest size of threaded rod they had,I think 1/2 inch,and locking nuts...we bent it around a tree about the same diameter as the axle and cut to length with a hacksaw--put them in,and drove it home!

    We all warned him that it was dangerous,and to fix it right before driving it any more--but his deaf ears didn't listen!--and just to make liars out of us,he beat that thing mercilessly the rest of the summer off road,and even plowed with it the following winter,without ever changing the threaded rod U-bolts!--and his axles were ABOVE the springs,which put tons more stress on the U bolts than when they are under them!...I still find it hard to believe the threaded rod held up--you'd think the threads would weaken it considerably--maybe he just had a gaurdian angel riding with him,I dunno! :dunno: :screwy:
     

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