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WHy grade 5 instead of grade 8?

Discussion in 'OffRoad Design' started by TX Mudder, Jun 11, 2002.

  1. TX Mudder

    TX Mudder 1/2 ton status

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    I just got my rear shackle greasable bushings.
    The first thing I noticed about them is they started life as grade 5 bolts. When did you guys start doing that?
    I have some front greasable bolts and they are grade 8.
    I can buy those same bolts (not drilled for the grease fitting of course) in a grade 8 for about 80 cents each at the local mom and pop hadware store, so it can't be a cost issue.
    Why the change?
    -- Mike
     
  2. kpanza

    kpanza 1/2 ton status

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    Just a guess, but I have heard a lot of people say that the only bad thing about Grade 8 bolts is that they are more "brittle" than Grade 5 hardware - the Grade 5 Hardware actually will "flex" a bit more before it would break, whereas the harder compound of the Grade 8 stuff would snap before bending...I'm sure Steve would give you Grade 8 if that is what it called for, as he doesn't cut any corners when it comes to quality...so I am sure he has his reasons!
     
  3. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    grade 8 has a higher shear strength. Whether on failure it would shatter rather than bend or whatever is best left to a guy who really knows his metalurgy... but in either case, in a shearing situation the grade 8 is unquestionably stronger and more durable. If grade 5 bolts do use a springy-er alloy, then it seems likely to me that said bolt would be an even worse choice... because LONG before a grade 8 bolt would snap, the grade 5 would be bent... which isn't good. I know when it comes to connections that are going to be off-road abused, I generally stick with grade 8 stuff. Tougher than hell, and really not THAT expensive.

    J
     
  4. ryanNC

    ryanNC 1/2 ton status

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    after installing lift kits for a couple years and putting on every manufacturer on the planet the best kits where from rancho. i think the reason there so high is the engineering and quality that goes into them. they used f-9 11 bolts.....aircraft strenth bolts my friends and i never ever broke one. it would strip out the threads out of the nut before it would mess up the threads. but on the grade 5 or 8 i think it's personal preference. have a nice day
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Grade 8 bolts will break long before a grade 5 will. But on the other hand a grade 5 bolt will bend long before a grade 8 will. Would you rather have a bolt break and not have any warning or have a bolt bend that you might possibly see and be able to replace before it breaks?
     
  6. mudhog

    mudhog THEGAME Staff Member Super Moderator

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    that was my thoughts /forums/images/icons/smile.gif id rather have it bend /forums/images/icons/smile.gif
     
  7. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    why exactly will a grade 8 bolt break before a grade 5? The later is speced to have a higher shear strength... so if the grade 5 fails at x psi (whatever it is).. and the 8 at 1.5x psi... why would the grade 8 one break first under any given load? Seems to me that before the grade 8 bolt broke, you'd have a grade 5 twisted into a pretzel (if the alloys used in grade 5 hardware are in fact as "springy" as they are being made out to be). Any resident metalurgy experts or hardware manufactures here?

    J
     
  8. Triaged

    Triaged 1/2 ton status

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    How about some more in depth analysis?

    The factory fasteners were grade 8
    They didn't have a hole drilled in them
    They were loaded in double shear on the shank of the bolt

    The ones that come with the greasable bushings are grade 5
    They have a hole drilled in them
    They are loaded in double shear but on the threads

    Shear strength of Factory fasteners:
    22,365 lb.

    Shear strength of greasable bolts:
    9,282 lb. (or 58% weaker)

    You say "But Dan. Those sleaves are what really take the load because they are clamped by the bolt in between the shackle."

    OK...lets look at that:

    Factory bolts were grade 8
    Factory bolts were fine thread
    Factory sleave has "teeth" on the ends (but lets pretend it didn't for the sake of this discussion)

    Greasable bolts are grade 5
    Greasable bolts are corse thread
    Greasable sleave is smooth on the end
    *I really don't think the hole drilled through the end has much to do with this case...the bolts will still brake at the root of the thread*

    The Factory sleave would slip at a load of:
    5945 lb.

    The greasable sleave would slip at a load of:
    2321 lb.

    From this you can see that the greasable sleave would slip at 53% of the load that the factory sleave would slip at.

    This would cause the hole to want to "oval" and wear out.
    That is what I worry about more. I would much rather use grade 8 bolts.
     
  9. Triaged

    Triaged 1/2 ton status

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    Grade 8
    Tensile Strength (when it breaks) = 150,000psi
    Yield Strength (when it starts to "bend") =130,000psi

    Grade 5
    Tensile Strength = 120,000psi
    Yield Strength =92,000psi

    As you can see a grade 5 bolt will bend and break before a grade 8 bolt will even start to bend!
     
  10. TX Mudder

    TX Mudder 1/2 ton status

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    I didn't know the exact numbers, but what Dan said is what I was thinking. Every bolt I remove from the truck I replace with grade 8, even if it is overkill, because it's cheap insurance.
    I honestly don't think I'll break the bolts, but if I were making them I would make them from a grade 8, just like the ORD greasable bolts that came with the HD front shackle.
    I want to say I'm not trying to dog ORD. I have several products from them (steering box brace, swaybar disc., and shackles) and the quality has been undeniably great and I have been consistenly impressed.
    But I would still like to hear from Stephen about the grade fives.
    -- Mike
     
  11. ken

    ken 1/2 ton status

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    I just broke a 1/2" grade 8 coarse thread bolt in my upper shackle mount on my Suburban...wasn't even off-roading! Anyways, what I have decided to do is to get a bolt long enough to where the shackle load point is not on any threaded portion of the bolt, therefore I will get too long of a bolt to where the shackle is on the solid (non-threaded) portion of the bolt. Then, since clearance around the shackle is a problem for me (exhaust, auto trans shifter, etc), I will cut off the threads past the nut. I think this will be the best way to insure against breakage. As I've said before, I cannot imagine a hollow (greasable) bolt being used in that application!!! Way too scary for me!!!
     
  12. Triaged

    Triaged 1/2 ton status

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    If it was a corse thread bolt it wasn't factory. Factory uses fine thread. Also the factory does what you are sugesting about the longer non-threaded portion of the bolt (they also use a thick washer/spacer to make sure the nut doesn't bottom out on the threads).

    Know the greasable bolts for the front are grade 8 and I think they are oversized too (9/16?) and that is how you can get away with a hole drilled in it.
     
  13. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    good #s Triaged, your final "grade 5 would break before grade 8 would even start to bend" analysis is what I guessed would be the case, but I wasn't 100% sure and I have a rule about not running my jibbs about something I don't KNOW about. /forums/images/icons/wink.gif Anyway, grade 8 rules. /forums/images/icons/laugh.gif

    J
     
  14. RaisedK5

    RaisedK5 1/2 ton status

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    Hey Dan, are those numbers for tension or shear. Arn't most bolts tested under tension conditions, underwhich Grade 8 is far superior, no question, less strech = greater clampload, etc. But are those tests indicitive of a shear condition in which the loading characteristics would be compleatly different, Grade 8s being harder and "more brittle" may have a higher tinsel strength under tension, but does that directly corrispond to shear resistance, Are these apples and apples and are there any specific shear numbers, because as i understand the numbers isn't yeild when it starts to strech, and tinsel when is breaks. Thats not exactly a shear situation. Whatcha think??
     
  15. Triaged

    Triaged 1/2 ton status

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    Yield strength in shear is generally assumed to be 1/2 of the yield strength in tension.
     
  16. RaisedK5

    RaisedK5 1/2 ton status

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    well then i guess that answers that /forums/images/icons/laugh.gif /forums/images/icons/laugh.gif /forums/images/icons/laugh.gif
     
  17. TX Mudder

    TX Mudder 1/2 ton status

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    Just wanted to bring this back up to see if anyone had any different input.
    -- Mike
     
  18. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    The GR5's come down to cost vs adequate strength. We started with an aftermarket vendor that ran gr5 for everything, even the drilled 7/16 bolts for the front shackles and found the 9/16 bolts held up without any problems. We went to 1/2" gr8 for the shackles just to get a decent size in there but cost for the bolts went up quite a bit due to the extra hardness of the material. We've now brought the bolt process in house with the intention of looking at gr8 for everything and sure enough, it's a pain drilling gr8 on a production basis. Our move to gr8 has been delayed till we can get the details sorted out. We still haven't had any problems with gr5 in the 9/16 size and problems with the drilled gr8 shackle bolts have been limited to 2, one was in what I would call a crash, the other one I just heard about online from someone on this post.

    Couple of details:
    I'm pretty sure the majority of factory suspension bolts are coarse thread. Shackle bolts seem to be fine, everything 9/16" seems to be coarse and though I don't have samples right here, I don't remember any funny thread lengths on the bolts so I doubt they're specially set up to ride on the shank of the bolt. Some tape measure work with known factory hardware will show for sure.

    Our drilled 1/2" bolts have been broken in tension and still come apart at the thread, not the head, so drilling doesn't have much effect on the overall strength of the unit.
     
  19. AgDieseler

    AgDieseler Certified Scrap Producer Premium Member GMOTM Winner

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    When that Miata ran up under me, it pushed the axle backwards on the D-side. That caused broken center pins, bent U-bolts, but also bent shackle bolts. They're the greasable 7/16 GR8, and the bent is small at the thread. All it took to separate the bolt from the sleeve was a few taps with a drift. Putting that in perspective, when I removed the spring from the main eye mount, It still had the original GR5 harware. For 17 years old, it was in pretty good shape, but was noticiably bent.

    Upon reassembly, I simply rotated the bolts around and shot them full of grease. Everything seems to be in great shape, so I'm not worrying as much about bent hardware as I am my bent frame.
     
  20. Triaged

    Triaged 1/2 ton status

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    Maybe I was wrong in thinking that every chevy is like mine...
    My shackle/spring eye bolts in the rear of my 1st gen were grade 8 fine thread and had a longer un-threaded portion (grip length) than a normal bolt of that size would have. The un-threaded portion of the bolt stuck out of the shackle by a bit and there were 1/4" thick washers under the nuts. Is this just another way chevy was getting cheep?

    BTW:
    1st Gen's Rule! /forums/images/icons/grin.gif
     

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