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What grade bolts?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 84k5, Aug 21, 2001.

  1. 84k5

    84k5 1/2 ton status

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    What grade bolts should I use for the factory tow hooks. I beleive Grade 8 has a higher tensile strength, but Grade 5 has a higher shear strength. Which would be better? Thanks.

    Brian
    <a target="_blank" href=http://84k5.coloradok5.com>84k5.coloradok5.com</a>
     
  2. Cavalry

    Cavalry 1/2 ton status

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    Shear Strength of a hex head cap screw is calculated at 60% of Tensile strength. The higher the Grade the higher the carbon content and through heat treating the 5's &amp; 8's the higher the strength level, but also the higher the "brittleness." The lower strength bolts are more "ductile" (have more stretch) than the higher strengths.
    I dont remember the diameter of the factory bolts but I believe they were pretty substantial. IMO you arent going to shear the 5's (a 1/2 inch fine thread grade five has a 19,200lb tensile which works out to 11520lbs shear X 2 bolts) or the 8's if properly installed. If you do you are going to have more problems than sheared bolts and flying towhooks.
    You have to remember these are towhooks, they were not intended to have loads like 75 foot of slack in the chain, going 45 MPH to pull some one out of the mud with a 4KLB truck.

    "There is a fine line between hobby and mental illness"
    Luke
    84 K5
     
  3. Pugsley

    Pugsley 1/2 ton status

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    Always use Grade 8 for tow hooks - preferably 1/2" or larger. In addition to increased strength, Grade 8's are far less susceptible to corrosion than other grades.

    Dos mas Tecates!!!
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  4. pcorssmit

    pcorssmit 1/2 ton status

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    There was a thread recently about shearing off these bolts. Lots of us have done it. Quite common.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Much rather have the bolts shear than the frame : )

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  6. BlazerGuy

    BlazerGuy 3/4 ton status

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    I have grade 8's on mine. The key is to use a good/big washer. The passenger side towhook is almost pulled through the frame, the bolts are just fine &amp; dandy.....

    ~~'84 K5~~
    Check it out at:

    <a target="_blank" href=http://www.k5.rockcrawler.com>www.k5.rockcrawler.com</a>
     

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