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is it ok to use a grade 5 fine thread bolt for the rear caliper brackets?

Discussion in 'The Garage' started by yunit, May 12, 2002.

  1. yunit

    yunit 1/2 ton status

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    Just wondering what everyone else is using with their conversion, I cannot seem to find a find thread grade 8 anywhere local.
     
  2. Twiz

    Twiz 1/2 ton status

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    I'm not totaly familure with the conversion. So, take this with a grain.

    I assume you are talking about the bracket that mounts to the axle houseing flange and holds the caliper in place. If that is the case, there should be 4 3/8s bolts - correct?

    I would think, a good quality, grade 5 or better bolt would be sufficiant. Keep in mind, rear brakes only appllie about 30% of the brakeing force, even less on a hard stop as the wweight transfers to the front. So, four grade 5 bolts should be plenty.


    Feel better now?/forums/images/icons/smile.gif
     
  3. Pure Insanity

    Pure Insanity 1/2 ton status

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    IMO this is your brakes your talking about. There is no such thing as making do, or settling for. Id say look further for grade 8 (or case hardened). The stronger the better.

    My bud had his caliper bracket welded to the housing, (this was long before anyone made brackets for this application) and twice he ripped the welds loose. (only 1 side gave him a problem for some reason) He had a hell of a time stopping a rig on 44s w/ one caliper spinning around loose.
     
  4. Pure Insanity

    Pure Insanity 1/2 ton status

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    I was typing when you posted yours Twiz, not to step on your toes, but to me when it comes to brakes, more is better.
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Not to pick on Eric...but I agree. Grade 8 fine thread should not be that hard to find, it's worth the extra hassle just for piece of mind. Save the grade 5 and less for door hinges and other non critical parts.

    Rene
     
  6. Twiz

    Twiz 1/2 ton status

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    Fair enough,

    It's my opinion that the 4 3/8 grade 5 bolts will be strong enough to hold the plates on rear of the truck. Plates that will only see 30% of the force at yhe most.

    It's not so-much the strength of the bolt, as it is the friction beteween the surfaces that keeps the parts togather. Think about it, If a 8-lug rim was tightend "finger" tight, it would still shear the studs, just as easy as a 6-lugger would.
    The bolts applie the pressure, the pressure appiles fritction, friction holds things in-place.

    I do, how-ever agree with you guys, it's better to build it stronger than you need it to be (grade 8s), but I woudn't think the rear brakes are stressed enough to shear 4 3/8s bolts.
    *quality bolts*
     
  7. 70~K5

    70~K5 1/2 ton status

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    But those bolts are in single shear, I wouldn't run less than grade 8.
     
  8. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    One thing to remember is that a grade 5 fastener will bend before it breaks but a grade 8 will break before it bends.
     
  9. Pure Insanity

    Pure Insanity 1/2 ton status

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    But there is a lot of stress there. I dont know #s as far as shear strenght and such but when I think of the torque applied to the caliper brackets by the leverage of a 38, I am just not so sure that a G5 would make it.

    But honestly what are the odds of a 38 getting sufficent traction and having enuff brake pressure to lock up?

    I understand your point of view of the pressure and friction, and yeah it would probably hold up but I wouldnt want to take a chance given there is something stronger out there. If there was nothing stronger, OK. But as long we are talking brakes, more is better.

    When I have to replace a rivited on spring hanger on a frame rail, there is no way to duplicate the rivits, so I use case hardened bolts, w/ crimp head nuts, no washers to risk squeezing out, THEN I will tack weld the nut to the bolt, tack the bolt head to the hanger, and tack the nut to the frame rail. I can assure you that bad boy aint movin.
     
  10. Pure Insanity

    Pure Insanity 1/2 ton status

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    I agree. BUT what are the odds of a bolt bending between 2 pieces of steel that are machined flat, that have exact size holes. There is no place to bend. That is where shear strength comes in.
     
  11. Twiz

    Twiz 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    I wouldnt want to take a chance given there is something stronger out there. If there was nothing stronger, OK. But as long we are talking brakes, more is better

    <hr></blockquote>

    Agreed.
     
  12. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I also agree with you. The odds of a bolt bending when two pieces are bolted together tight with exact fitting holes is almost a non heard of thing. On the other hand, when referring to different grades of bolts most people are referring to the tensile strength of the bolt not shear strength or torsional strength. I will add, use the same grade bolt that was originally used from the manufacturer.
     
  13. Goober

    Goober 1/2 ton status

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    Grade 5's would possibly be ok.

    But with my wife and 2 year old son in the truck with me looking down a 500 ft cliff ....

    .... I WANT GRADE 8's !!
     
  14. Triaged

    Triaged 1/2 ton status

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    I don't even like using grade 8! I was thinking of going w/ AN bolts! The factory bolts are short and clamp the backing plate directly onto the axle. When you do the disc swap you have spacers and longer bolts (the brakes have more leverage to try and brake the bolts because they are longer...so it isn't really just single shear but bending and shear). Add to that the fact that the grade 8 stuff you can buy now is mostly made in China and the bolts on your truck were US made...There is no way in hell I would use grade 5!
     
  15. Twiz

    Twiz 1/2 ton status

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    If there is a spacer, than there would be more-bolt to stretch and that means it has a higher ability to provide more clamping force and retain that force longer. (insted of "relaxing")

    Again, My point is:
    It's not the bolt, it's the friction.

    Don't get me wrong though.../forums/images/icons/smile.gif
    I think the grade 5 would be O.K., grade 8 would be better.
     
  16. Triaged

    Triaged 1/2 ton status

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    If you are going by friction then you should still go w/ grade 8 because you can tighten it down more to create more friction then the grade 5.
     
  17. yunit

    yunit 1/2 ton status

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    Thanks fellas, grade 8 it is.
     
  18. Pure Insanity

    Pure Insanity 1/2 ton status

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    Who woulda guessed thered be so much talk about bolts! /forums/images/icons/tongue.gif
     
  19. thatK30guy

    thatK30guy 1 ton status Premium Member

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    BTW, those 14FF flange bolts are 1/2", not 3/8". /forums/images/icons/wink.gif

    Why not give ARP a call and get some of their indestructable bolts? Their bolts are strong enough that they are used as engine fasteners. /forums/images/icons/wink.gif
     
  20. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Minimum tensile strength of a grade 5 bolt is 105,000 psi vs. 150,000 psi for a grade 8. By those numbers, I would feel safe using grade 5.

    John
     

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