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Hot Rods Single shear

Discussion in 'The Hokey Ass Message Board' started by 2OLD2FAST, Oct 19, 2020.

  1. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,722

    from illinois

    I see numerous negative comments about things mounted in single shear .It seems to me that every conventional tie rod end , ball joint & probably a majority of shock mounts are single shear without problems. , Comments ?
    Blues4U likes this.
  2. alchemy
    Joined: Sep 27, 2002
    Posts: 15,850


    Every purpose will have its best design. Hopefully we can meet the best design, or come close. Some guys overcompensate.
    1934coupe likes this.
  3. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 1,711

    from New York

    Exactly, if it is designed and built with the correct hardware it's fine.
    1934coupe and Blues4U like this.
  4. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,854

    from Oregon

    And it depends on the forces applied to the single shear. I wouldn't want coilover shocks done as single shear, but shocks assisting spring suspensions work with single shear. So just know how strong it needs to be, and then decide if it needs double or single shear.

  5. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,055

    Mike VV
    from SoCal

    As said, IF...designed correctly...

    The factories spend a LOT of money and time designing, and testing this stuff.
    Materials, material sizes, cross sections, attachment points, attachment methods.
    The steering points don't have THAT much strain on them. The big piece of rubber between you and the ground soaks up a lot...of shock and load that would otherwise beat on a solid mount.
    A shock or especially a coil-over shock, spring mount can have a lot of car weight AND dynamic weight on it.

    A simple 3/8" or 1/2" fastener (no matter the grade) in single shear attached to a piece of 1/8" to 3/16" thk. flat stock material, that isn't properly heat treated (NOT soft 1018/1020 steel), is NOT a good idea if yours or anyone else's life depends on it. They bend and flex with loading.

    Ever tried bending a piece of metal back and forth...till it breaks..?


    pitman likes this.
  6. The reason those applications you site are OK is because the engineer calculated the loads and stresses for that particular item, and determined the combination of materials used and loads/stresses to within the design limits and safety factors approved by the company Chief Engineer. Material fracture and fatigue of properly designed parts are pretty much non-existent these days.

    Any component that will be hazardous to life and limb when it fails needs to be designed by a competent person. Shade tree engineering of those parts can be (has been) disastrous.
    warhorseracing likes this.
    Joined: Dec 14, 2009
    Posts: 2,665


    As has been stated car manufacturers have battalions of engineers to think of every possible failure point and failure scenario.

    A “shade tree mechanic” does not have this luxury, so over engineered is better when your not sure is my guess and the way I usually do things.

    my dad is one of those over engineering types . When he builds stuff around the house his go to line it “ you can put the CN Tower on ———- whatever it is he built .

    Blanket statements are dangerous, just like under building something.
    Just know what your building and build it to a quality standard I guess is what I’m getting at.

    paging @gimpyshotrods he’s usually clear and concise on these topics.
    Last edited: Oct 19, 2020
    alanp561 likes this.
  8. As most modifications that are done and posted on this sight are probably not designed and tested for strength by an engineer the "blanket statements" err on the side of caution so the guidance people are getting is the safer alternative and has very little to do with close mindedness.
  9. Budget36
    Joined: Nov 29, 2014
    Posts: 4,203


    Well, my take is shocks have been in single shear forever. Shocks don’t carry the work. Coil overs like in a tribar, etc, carry the load And should be in double shear. Leaf springs aren’t mounted (in modern production) in single shear.

    There’s a lot of factors at work when a vehicle is moving down the road. What works on a dirt track, circle track or drag strip, isn’t the way to build something that will be taking trips across country, etc.

    So I would ask, is it safer to over build, or do what they have seen that works?

    My thing is I’ve never done anything thinking of “the other guy”. But always thought of myself. I figure if if safe for me and mine, should be safe for all
  10. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,866

    from So Cal

    About a bazillion out there installed single shear. When was the last time you heard of a catastrophic failure?
    2OLD2FAST, Chicster and seb fontana like this.
  11. seb fontana
    Joined: Sep 1, 2005
    Posts: 6,591

    seb fontana
    from ct

    I discovered my motto over the years has been, "when in doubt make it stout". I look at some stuff I built and say to myself what was I thinking, thats about twice whats needed. I was thinking I didn't want it to break; 40 years later it hasn't so good enough.:)
    alanp561, thintin, bchctybob and 3 others like this.
  12. Nostrebor
    Joined: Jun 25, 2014
    Posts: 1,073


    Automakers put things in single shear because they have engineers to verify loads on such things, and accountants to tell them just exactly how much that extra tab of steel will cost.

    Shade tree hot rod builders put things in double shear because we often have neither of those things on staff.:D

    In all honesty, I use both as is appropriate, and do occasionally run a calculation or two to check a design I'm considering. I don't have the luxury of welding robots and production facilities, so sometimes the extra tab of steel wins out simply to help me sleep better at night. I am after all, doing this hobby labor for free!
  13. grumpy65
    Joined: Dec 19, 2017
    Posts: 371


    Look at the potential consequences of a failure of the varying parts/brackets.
    Shock absorber bracket failure is not usually a catastrophic event.
    Spring mounts, however, are part of the 'load carrying' setup in a vehicle, and failure here can be a very bad situation for your health, and anyone elses health that is in the immediate vicinity. This should scare you!!! :eek:
    I guess the way I look at it is, if I fear the possible outcome of a failure (load carrying suspension, steering, brakes, wheels and tires) I will always engineer to above the minimum required level. It's too late when it's too late. :oops:

    By the way, I do everything in double shear, but that's just me. Looks better, works better, feels better, and I sleep better at night. :D
    Last edited: Oct 19, 2020
    alanp561 and VANDENPLAS like this.
  14. fiftyv8
    Joined: Mar 11, 2007
    Posts: 5,119

    from CO & WA

    How about a technical definition of what single shear is and a couple of pic's showing it (good & bad examples) for the audience.
  15. 19Fordy
    Joined: May 17, 2003
    Posts: 6,919


    Joined: Dec 14, 2009
    Posts: 2,665


  17. grumpy65
    Joined: Dec 19, 2017
    Posts: 371


    Surely we are not going to turn this into a pissing contest regarding semantics.
    For your benefit: "I do everything I possibly can in double shear."
    Happy now?
    Budget36, TA DAD and VANDENPLAS like this.
  18. grumpy65
    Joined: Dec 19, 2017
    Posts: 371


    Here's the lowdown and skinny on hand-built vehicles, as I see it.

    If it is only going to be trailered to shows, or you are only going to drive it around your own back yard, do as you please. If it all goes tits up, it will hopefully only be your ass on the line.

    If you intend to use your pride and joy out in the public arena, you have a certain level of responsibility for the safety of others around you. This includes public roads and race tracks. Scrutineering is there for a good reason.

    Here is a 'blanket statement' that I can live with - "Build it like your life depended on it". ;)

    Single vs double shear - That one small extra piece of metal that is inexpensive, light, and takes very little time to install, contributes a great deal to the strength of the mount. Why would you choose not to???
    Last edited: Oct 19, 2020
  19. Budget36
    Joined: Nov 29, 2014
    Posts: 4,203


    We said the same thing;)
    grumpy65 likes this.
  20. nutbush
    Joined: Jul 7, 2006
    Posts: 257

    from Texas

    Jim Jacobs designed the PJ coil over mount top and bottom single shear and that design was 45 years ago. If you know how to weld correctly and use grade 8 bolts, single shear works fine.

    Sent from my iPhone using The H.A.M.B. mobile app
    Blues4U likes this.
  21. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,136


    Uh, OK.
  22. When did "single shear" become a bad word?
    ..only when an under-designed part was asked to do more than it should.

    Sent from my SM-G981V using The H.A.M.B. mobile app
  23. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 2,664

    Lloyd's paint & glass

    I'm just a retarded bodyman, but doesn't it depend on how much force the said connection is gonna have to endure repeatedly? Like a leaf spring bolt being setup in double shear and a tie rod end being single?
    deucemac, grumpy65 and VANDENPLAS like this.
    Joined: Dec 14, 2009
    Posts: 2,665


    This has become a 43B4F733-2B9A-402F-AF55-92C635B6C931.jpeg

    just like the wheel , rim, tire attachment fitting.
    Freeze plug, frost plug, blanking plug, Welch plug butt plug fiasco .

    gosh, we’re all adults can’t we just tell each other to duck off and get back to our regularly scheduled programming ?

    alanp561, lumpy 63, fauj and 3 others like this.
  25. Halfdozen
    Joined: Mar 8, 2008
    Posts: 606


    As much as possible, I try to use fasteners in double shear. Sometimes, it's very difficult, as in lower mounts for coil shocks. I always make up a substantial spacer to go between the shock eye and the housing bracket, it offers support very close to the shock body. I always use 5/8 grade 8 bolts here too. Coil shock mounts 003.JPG Coil shock mounts 007.JPG Coil shock mounts 009.JPG
  26. grumpy65
    Joined: Dec 19, 2017
    Posts: 371


    ^^^ Very nice work. Excellent examples of how to do single shear. :cool:
  27. Pete Eastwood
    Joined: Jul 27, 2011
    Posts: 960

    Pete Eastwood
    from california

    Well done !
    deucemac likes this.
  28. patterg2003
    Joined: Sep 21, 2014
    Posts: 620


    2old2fast. You got the answer in that the applications in your example are engineered then the design allows for all the stresses. The advantage of the double shear is that there are 2 cross sections to share the stress, The fastener in double shear can be a smaller diameter to carry the stress of a larger cross section in single shear. Every type of connection has its purposes and pros or cons. It seems a very generic question looking for an argument and whenever anyone attempts to answer then your response is to growl. Growl on.
    stanlow69 and grumpy65 like this.
  29. X-cpe
    Joined: Mar 9, 2018
    Posts: 998


    When all is said and done, I hope everyone has built their stuff safe and strong because when you are out there you are aimed at me and mine.
    Last edited: Oct 20, 2020
    VANDENPLAS and grumpy65 like this.
  30. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,758

    from oregon

    Looks familiar!

    I have three cars with coilover suspension, two of them both front and rear, and the one thing that I never cared for is the (typical) single shear mount system offered by most builders on the lower coilover mount for the rear of cars.
    Grade 8 hardware or not, that is asking a lot out of a bolt, especially on heavier cars.
    The problem is also made worse when spacers are used for extra clearance, this added "slip surface" has a built in loosening effect.
    One other dangerous practice often seen is having bolt threads as a load bearing surface creating another loose situation as the thread erodes.
    Many years ago these simple little mounts appeared on the market and I finally thought "somebody was think'n", these are a good way to spread the load over two mounting bolts and also combat the self loosening effect.


    Problem was, $50.00 sure could go a long way on other part purchases so I made these.


    Attached Files:

    Last edited: Oct 19, 2020

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