What grade/class bolts for suspension HW?

Discussion in 'Gen 1 & 2 - Suspension, Brake Systems, & Body' started by jayro, Feb 13, 2013.

  1. jayro

    jayro Well-Known Member

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    I was wondering if anyone knew what grade/class bolts should be used for suspension hardware. I know you don't want anything too hard because they will break instead of flexing in high load situations.

    Would grade 8 be good of should I use a standard grade 5?

    Also, from reading I found that Class 10 is about equal to grade 8. Can anyone with experience verify this?

    Thanks
     
  2. zak

    zak SHO Member

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    Ideally you want OEM bolts for any suspension application. A Grade 8 will be strong but brittle. Any Grade 5 bolt wil be weak in this application.
     
  3. jayro

    jayro Well-Known Member

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    Then what Grade are OEM bolts? Somewhere in the middle?
     
  4. zak

    zak SHO Member

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    Automotive suspension fasteners don't correspond to SAE or metric strength grading systems, they are made under very different standards for quality control, strength vs. elongation to failure, hardness etc. Remember that for many of these suspension applications if the bolt fails then control of the car can be lost at speed. They are typically optimized for both strength in shear, and elongation to failure.

    If you stuck with having to buy bolts for a uniquely engineered suspension modification go with NAS or AN aerospace rated fasteners. Aircraft Spruce, Pegasus Racing are a couple of sources.

    Something to read would be this:
    http://www.amazon.com/exec/obidos/t...f=sr_1_1/002-0119510-8760844?v=glance&s=books
     
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  5. AREA 91

    AREA 91 PA SHO SHOP

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    I believe the stock bolts are a 10.9 rating.
     
  6. jayro

    jayro Well-Known Member

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    That would be Class 10.9, correct? The metric ones I have found are defined by "Class" and the SAE seem to be "Grade".

    The conversion I found shows that a class 10.9 is about a Grade 8.
     
  7. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    ^ This is misleading at best, and quite incomplete.

    Grade 8 bolts are approx 130,000 psi yield strength, which is very strong. A properly made grade 8 bolt will not be brittle. However, if you zinc plate or chrome plate a grade 8 bolt, it can become brittle - that is why you do not find quality grade 8 fasteners that are plated. Grade 8 bolts are identified with 6 equally spaced radial lines on the head.

    Grade 5 bolts are approx 90,000 psi yield strength, which is not 'weak'. A grade 5 bolt will elongate noticeably before breaking in most cases - much more than a grade 8 bolt will. Grade 5 bolts are identified with 3 equally spaced radial lines on the head.

    The material from which they are made is different, grade 5 being medium carbon steel and grade 8 being medium carbon alloy steel. The addition of the alloying materials allows the grade 8 bolt to be hardened to the higher yield strength without becoming 'brittle' - whereas if you try to harden a grade 5 bolt to the grade 8 properties, it will be fairly brittle.

    Grade 1 or 2 bolts, on the other hand are not nearly as strong - they have yield strengths of around 36,000 and 57,000 psi respectively. They will elongate significantly before breaking. Grade 1 or 2 bolts do not have any radial lines on the head.

    Metric class 8.8 corresponds roughly to grade 5 SAE bolts, and metric class 10.9 corresponds roughly to grade 8 SAE bolts, with metric 9.8 between them. Metric fasteners simply have the class rating on the head.

    If you look at the markings on the factory fasteners on our vehicles, you will find many more 8.8 markings than 10.9. Therefore, in most locations, the factory engineers deemed 8.8 to be plenty strong enough for our applications.
     
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  8. zak

    zak SHO Member

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    I will concurr that my post was incomplete, but the OP didn't note which fasteners he was attempting to replace.

    First point is you are quoting tensile yeild strengths, when most of these fasteners are loaded in shear.

    Secondly, if you think that the Grade 5 bolt at your local hardware store has the same overall reliability that an automotive OEM bolt that might have an 8.8 stamped on its head (since it happens to also meet this spec along with others) you are sadly mistaken. In fact, if you're using hardware store Grade 5 bolts to hold your suspension together I for one do not want to be on the same road or track as you.

    All I have time for right now.
     
  9. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    yield strength of material is relevant regardless of what manner the material is loaded. yes, some materials have different yield strengths depending upon how they are loaded (concrete being a good example of this) but heat treated steel is not one of those materials.

    the only person in this thread who talked about hardware store fasteners is you. I talked about quality fasteners, which are available at some hardware stores, but when I want to ensure quality fasteners I go to somewhere like Fastenal that only does fasteners for their business. it is very difficult to find a hardware store that sells grade 8 or class 10.9 fasteners anyway.

    and, btw, the industry has done a pretty good job of getting rid of the suppliers who provided junk fasteners labelled as grade 5 or grade 8.

    edit:
    Sorry I wasn't more complete above...

    The shear strength of the steel bolt (regardless of grade/class) is about 60% of the tensile strength so the relative difference in the strength of the fasteners is the same.
     
    Last edited: Feb 14, 2013
  10. Racer X

    Racer X SHO Pilot

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    Semantics aside, I recommend class 10.9 hardware for suspension applications.

    On where to purchase, I prefer Metric and Multistandard Components Corp (http://www.metricmcc.com), but only because there's one relatively local to where I am and they solely deal with metric fasteners. If you're close to a Fastenal, that's a good bet also.
     
  11. frosho

    frosho WOLFMAN

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    Belmetric.com is another great fastener/hardware store that is local to me. They specialize in metric and automotive applications, and a lot of local dealerships get their hardware from them.
     
  12. jayro

    jayro Well-Known Member

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    Thanks for all the input guys. I have both a Fastenal and an ACE here locally. They both carry hardened metric fasteners. I am installing my adjustable rear control arms and h-brace. I may be able to use all the OEM hardware, but I was looking at my other options if the bolts looked bad after I de-rust them in my glass bead cabnet.
     
  13. Toolman

    Toolman Boost it! Staff Member Club Mod

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    I can still send you out the ones I found. Then there are no questions about it.

    And they are free.

    Also, there is a local Ford parts distribution warehouse here that I get all my bolts from.
     
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  14. AREA 91

    AREA 91 PA SHO SHOP

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    The past 2 cars that have been "restored" in my shop we used all grade 8 fasteners from Fastenall.
    Lucky for me it's across the street. :)
    These were 60's GM cars.
     
    Last edited: Feb 14, 2013
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  15. jayro

    jayro Well-Known Member

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    Thanks. I thought I had some extras in my stash....but I was wrong. If you don't mind sending them out that would be great. I will shoot you a PM with the address.
     

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