Fastener advice needed

[gjk5]

I know, I know: "GRADE 8". It's not that simple (I think). I have pulled my old swing away tire carrier on my '72 K5 and stripped and repainted it and am wanting some input on re-mounting.

Sorry, I don't know how to draw and post a diagram so here goes:

It originally had a 7/16" grade 5 bolt, large fender washer, upper arm of swing away, mount bracket, lock washer and finally the nut (this is from top to bottom) through a 1/2" hole.

The bolt sheared when I removed it (it may have had something to do with the 2 three foot breaker bars I used) but it was fully threaded with the threads all eaten up from movement and nothing to really help with not binding.

My idea was start with grade 8 in a smaller diameter slipped through a 1/2" steel sleeve spacer (at just enough length to go through arm and mount bracket) to keep it from binding using the same washers to try and "trap" the spacer, so it works kinda like an axle. I'm wondering if the spacer is going to create a weak spot in the setup (and I couldn't find grade "anything" spacers)




Or should I just keep it simple and cram a grade 8 1/2" bolt with no thread at the top in there and will this cause binding as well since the hole's only 1/2"?

Or just shut up and stick with the original set up @ 7/16" in a grade 8 and stop trying to complicate things?

 

[gjk5]

Great. Thanks anyway, guess I'll just have to deal with some nimrod at Western Implement rather than someone who just may have application specific experience with this.

 

[Triaged]

you could have waited more then 3 hours before giving up...

I would stick with the 7/16" bolts but use fine thread grade 8. It will leave you with enough wiggle room to get it lined up right. Using large fender washers is good but using a piece of sheet metal back there along with the fender washers would help spread the load better. Make sure you torque the bolts down well (78ft*lb if you use the bolts I sugested) and check them after driving around a while. Some anti-seze should keep the bolts from rusting out to quick.

 

[gjk5]

It wasn't the three hours, it was the 49 something views.

Thanks for the reply though, I think I am going to try to just find one with the appropriate unthreaded shoulder just so there are no threads getting mangled.

I did go to a couple stores and the fastener "expert" at the tractor supply store actually told me that the grade 5 was better and stronger for that application as the grade 8 is more for longitudinal strength and more prone to shear than a grade 5.

What the hell is with that?

 

[jekbrown]

It wasn't the three hours, it was the 49 something views.

ya have to give posts in the garage a chance. Lots of people probably looked and didn't have anything to contribute, so they didn't post up. This is actually a good thing, you don't want people who don't know what they are talking about giving you tech advice. Additionally, without a pic, diagram or something to go by, its a little hard to figure out exactly what you're trying to do. If ya need a pic posted, thats no problem, I can do that for you if you email it to me ([email protected]). It would help a lot and you'll get more responses that way because people will know what you're asking.

I did go to a couple stores and the fastener "expert" at the tractor supply store actually told me that the grade 5 was better and stronger for that application as the grade 8 is more for longitudinal strength and more prone to shear than a grade 5. What the hell is with that?

classic example of someone not knowing what they are talking about. Grade 8 is stronger is shear... and every other way you can load it. When a grade 5 fails, sometimes it will bend before breaking... some people mistake this for the bolt being "tougher" than a grade 8. What they don't realize is that at the same force the grade 5 is bending (and will fail completely soon) the grade 8 hasn't even started to fail. When it does, it will probably just break rather than bend very much... but all of that happens after a gr 5 bolt is beyond toast.

in any case, if I was you, I'd probably go with new grade 8, 1/2" bolts, good washers (hardened ones if you wanna spend the $) and lock nuts. If the hole is 1/2", and they all line up correctly, 1/2" hardware ought to fit just fine. If it doesn't, it shouldn't be tooo much of a hassel to hog one or two out using the carrier as a guide.

j

 

[dremu]

It wasn't the three hours, it was the 49 something views.

Thanks for the reply though, I think I am going to try to just find one with the appropriate unthreaded shoulder just so there are no threads getting mangled.

I did go to a couple stores and the fastener "expert" at the tractor supply store actually told me that the grade 5 was better and stronger for that application as the grade 8 is more for longitudinal strength and more prone to shear than a grade 5.

What the hell is with that?

If I understand it, grade 8 stuff is high tensile strength -- I think that's the word for pull, right? -- but more brittle, so the shear (side-to-side) strength isn't there.

As opposed to sheer strength, which is a typo I see all the time. Angers me almost as much as "gear rations" -- are those what you feed your gears?

Anyway, grade 5 hardware has a higher shear strength and/or is less brittle, so it will bend and deform, when grade 8 would just snap. I decide which hardware to use based on what I want the failure mode to be, what loads it will see (lateral or longitudinal), and what I have right there in the box in front of me so I don't have to drive to OSH again (for the fourth time today)

As for your specific thing, my cheeseball dealer-installed carrier had random nuts and stuff in it when I got, but one thing to note was that it had three washers -- one under the bolt head and one behind the nut, like yours, but also one between the mounting bracket and the swing arm. If I was gonna put the thing back on, I'd grease the hell out of that area, but I found that I didn't have to tighten it all that much to have it work well for me.

HTH.

-- A

 

[jekbrown]

If I understand it, grade 8 stuff is high tensile strength -- I think that's the word for pull, right? -- but more brittle, so the shear (side-to-side) strength isn't there.

Anyway, grade 5 hardware has a higher shear strength

negative.

and/or is less brittle, so it will bend and deform, when grade 8 would just snap.

if you applied the exact same amount of force that was just enough to snap a grade 5 bolt... the gr 8 bolt would still be a-ok. Its stronger in shear even if it is more brittle.

I decide which hardware to use based on what I want the failure mode to be, what loads it will see (lateral or longitudinal), and what I have right there in the box in front of me so I don't have to drive to OSH again (for the fourth time today)

me thinks factor 3 is the prime consideration...

j

 

[gjk5]

Thanks guys, I'll wait a little longer next time. I usually post these ?'s in the 1st gen forum where the views and responses are much slower, I'll wait a little longer in the garage next time too.

Jekbrown: I know how to post a pic, I was just at work and didn't have access to one, but I am monkeying with the computer to figure out how to post a diagram (I know how to draw in ms paint)


Thanks for clarifying the 5 vs 8 thing, I figured that as usual the guy at Murdoch's (or Home Depot or Lowes or whatever idiot I'm talking to) didn't know much of crap about crap.


Shouldered grade 8's it is. I actually found them in a black oxide finish rather than that gold zinc oxide, now I just need washers in black too.

 

[dremu]

if you applied the exact same amount of force that was just enough to snap a grade 5 bolt... the gr 8 bolt would still be a-ok. Its stronger in shear even if it is more brittle.

Dammit, I knew somebody who knew something would post up just as soon as I did

Thanks JB ... I stand corrected.

me thinks factor 3 is the prime consideration...

j

LOL, especially for something like a tire carrier which doesn't see huge loads. Now, for bumpers or rollbars or my CUCV shackles, you betcha I use the good stuff... but otherwise, whatever's handy works

-- A

 

[jekbrown]

LOL, especially for something like a tire carrier which doesn't see huge loads. Now, for bumpers or rollbars or my CUCV shackles, you betcha I use the good stuff... but otherwise, whatever's handy works

yeah, if the engineers at gm decided a grade 5 bolt was enough for the tire carrier... it probably is. Of course, they don't design things for oversized tires. If it was meant to hold a 31" tire... maybe a 33" is pushing it with respect to fastener tech. who knows. For anything that really bears any weight/force I always go with grade 8 on my rig.

j

 

[ntsqd]

classic example of someone not knowing what they are talking about. Grade 8 is stronger is shear... and every other way you can load it. When a grade 5 fails, sometimes it will bend before breaking... some people mistake this for the bolt being "tougher" than a grade 8. What they don't realize is that at the same force the grade 5 is bending (and will fail completely soon) the grade 8 hasn't even started to fail. When it does, it will probably just break rather than bend very much... but all of that happens after a gr 5 bolt is beyond toast.

I am one of those who proposes a G5 in certain situations. There are places I'd rather have a bent G5 than a sheared and lost G8. G8's are more brittle than G5's so an impact load that would bend a G5 will shear a G8. Better a bent bolt than no bolt.
The big caveat here is that b/c a G5 has a lower tensile you HAVE to use a larger bolt.

If I understand it, grade 8 stuff is high tensile strength -- I think that's the word for pull, right? -- but more brittle, so the shear (side-to-side) strength isn't there.

Shear Strength is a direct function of Tensile Strength. The relative brittleness of a bolt is only a factor in extreme overloading where it will predict the failure mode, but not necessarily the failure load.

Pivoting on a bolt is cheap, but not good engineering. Make a sleave to go thru the hole in the moving part only. Tighten the bolt thru the sleave and clamp it to the base bracket.

 

[gjk5]

Pivoting on a bolt is cheap, but not good engineering. Make a sleave to go thru the hole in the moving part only. Tighten the bolt thru the sleave and clamp it to the base bracket.

Good to hear, that was one of my thoughts in the original post. I'm calling around trying to find a strong steel sleeve or spacer since the shops I already checked only had plastic, aluminum and brass.


Thanks for all the advice, I gotta loosen up, if I'm this anal about every bolt I'll never get the truck finished.

 

[diesel4me]

sleeve?

I use pipe for sleeves all the time--or old wrist pins,(brittle!),and bushings from old lawnmower wheels--chevy smallblock valve giudes work for 3/8 bolts!--.if you have a home depot or lowe's,they have a limited selection in their "drawers" in the hardware section of steel bushings..my favorite store for stuff like that is a local farm store,similar to "Tractor Supply"--they have a lot more to choose from,and are MUCH more reasonably priced--I had to pay 7 bucks for 1 bolt at lowes for my engine crane--1"x6 inch grade 8!---the Farm store had the same thing for 2.99 --but Lowes is 1/2 mile away,the farm store is 12 miles--

 

[jekbrown]

I am one of those who proposes a G5 in certain situations. There are places I'd rather have a bent G5 than a sheared and lost G8. G8's are more brittle than G5's so an impact load that would bend a G5 will shear a G8. Better a bent bolt than no bolt.

this assumes that the G5 will actually still be in one piece (tho bent) when the G8 "shears". Of course it depends on a lot of factors, but I wouldn't make that assumption. IMO, in a majority of failures, the gr5 would have failed completely before the gr8 will. If a broken bolt is better than a non-broken one... well.. yeah. lol!

The big caveat here is that b/c a G5 has a lower tensile you HAVE to use a larger bolt.

comparing a larger gr 5 vs a smaller gr 8 doesnt make any sense. If you can use a larger bolt, use a larger gr 8.

j

 

[ntsqd]

jek, It makes plenty of sense. The idea is that you need an XX,XXX psi shear strength bolt. Two ways to do that. Either use a higher strength, smaller diameter, more spendy bolt, or a lower strength, larger diameter, less spendy bolt. Assuming that you do the calcs, either method results in a strong enough bolt.

The point I haven't (yet) made clear is that I do NOT trust G8's. If the application is a critical one I go right to something better than any SAE rated bolt, regardless of grade. Can't justify doing that on a tire carrier so I hadn't mentioned it.

People tend to think that a G8 is the Holy Grail of bolts. It is not, its not even close. The common socket head cap screw (aka "Allen" bolt) is both stronger AND more Ductile than a G8 bolt. It's the first bolt type I look at in a bolt critical application. I would sooner use a SHCS than a G8 in just about anything.

 

[loafer]

Shear Strength is a direct function of Tensile Strength. The relative brittleness of a bolt is only a factor in extreme overloading where it will predict the failure mode, but not necessarily the failure load.
.

A bolt loaded in "shear", such as a bolted lab joint, the tire carier exaple, etc., has the same stregth as a bolt loaded in tension.

The "shear strength" of a bolt determines how much torque the bolt can handle (not the tightening torque though...this is different because the nut is rotating w/ respect to the bolt) Usually the only time a bolt fails in torsion (pure shear) is when the threads are rusted, you try to loosen the nut, and the bolt "twists" off.

 

[jekbrown]

The point I haven't (yet) made clear is that I do NOT trust G8's.

if you can't "trust" something industry rated, then it seems to me that paranoia wouldn't allow for any type of bolts to be used, no matter what grade/spec they are, after all how could you trust them?

If the application is a critical one I go right to something better than any SAE rated bolt, regardless of grade. Can't justify doing that on a tire carrier so I hadn't mentioned it.

there is no question that there are better alloys out there, the 190,000 psi stuff that ARP uses for example. Pretty much all the fastener manufacturers have some uber-alloy hardware. I'm not saying that gr8 is the end all and be all of hardware... if anything Im suggesting that its the weakest option that should be considered for most automotive applications.

People tend to think that a G8 is the Holy Grail of bolts. It is not, its not even close. The common socket head cap screw (aka "Allen" bolt) is both stronger AND more Ductile than a G8 bolt. It's the first bolt type I look at in a bolt critical application. I would sooner use a SHCS than a G8 in just about anything.

yeah yeah we all know about the bling allen bolts, but not all applications need a fastener beyond grade 8. Steering arm studs are a good example... but there aren't toooooo many other places on a k5 where I think uber hardware (read uber $pendy) is necessary. If you want to hold your glovebox on with super bling 1" allen bolts go for it!

j

 

[Tom E]

Hate to pull up an old thread, but I have a question related to this. I'm doing the 52" leaf springs from the rear and putting them in the front. My local bolt store had G8 bolts and washers in stock but will have to order G8 locknuts. Do I need to use G8 locknuts or not? I'm using this article as my instructions:
http://www.coloradok5.com/52inchspringswap.shtml

 

[kennyw]

Tom any smaller hardware store with a good bolt selection will sell you grade 8 locknuts... Just look for an Ace or TrueValue hardware or something like that.

But for the original thread... Jekbrown is right and if you can follow this article below it explains it well.
http://www.rockcrawler.com/techreports/fasteners/index.asp

 

[ntsqd]

A bolt loaded in "shear", such as a bolted lab joint, the tire carier exaple, etc., has the same stregth as a bolt loaded in tension.

From the link above:
"Mark’s Standard Handbook for Mechanical Engineers lists Grade 5 fasteners as 120 ksi fasteners. This means the tensile strength is 120,000 lbs per square inch. It also lists Grade 8’s as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength."

If I understand what you're saying correctly either you or Mark's is wrong.

if you can't "trust" something industry rated, then it seems to me that paranoia wouldn't allow for any type of bolts to be used, no matter what grade/spec they are, after all how could you trust them?

It isn't that I don't trust the SAE std, it's that I don't trust the source of the bolts. There have been WAY too many cases of counterfeit bolts making their way into places where they should have been caught. There is no way I can hope to determine if a bolt is counterfeit on my own. So for critical applications (glovebox door not being one of them) I go to a bolt that I can trust the origin of.