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Looking for some insight. My trailer has Grade 8 hardened bolts in the suspension and undercarriage. While in on a trip I hit a bump and one of the bolts snapped in half. Needless to say causing a pain in the butt to fix while on the road.

The question is, now that I have time this winter, should the bolts be of a less hardness to minimize the tinsel strength and thus allowing the bolts to give a bit instead of snapping?
 

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Grade 5 should be good enough for that trailer. Must have been some bump !


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I would go with either a slightly less hardened bolt or I have good luck with stainless steel bolts with an aircraft nut, the nuts with the neoprene in them. Although the stainless is more expensive, there are only a few areas that I would put them on, hitch and suspension would be two of those areas, so your not spending that much more.
 

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bolts whether grade 5 or 8 have a point where stretch factor is involved,overtightening can cause premature failure,which is probably what happened in this instance,there are charts in most manuals which suggest normal torque figures,but manufacturers websites usually have posted figures
 

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From a parts catalogue.
 

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mr irrelevant
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I thoroughly believe, because i have ridden with Tim and his lovely wife on two trips last summer, that he should get the hardest darn bolts he can get, because if its possible for it to happen, it will!!LOL...Just ask me bout my glasses, I have proof!! LOL....now back to your regularly scheduled thread , please help Tim with his dilemma and tell him to post pics of his newly installed LED dash lights!!
 

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Trainertim77 wrote:
Looking for some insight. My trailer has Grade 8 hardened bolts in the suspension and undercarriage. While in on a trip I hit a bump and one of the bolts snapped in half.


Are you referring to "U-Bolts" or Shackel EyeBolts?


In any event. Grade 8 is better suited than grade 5 for these applicaitons. If it was your U-bolt then the failure was in tension. If it was the Eye Bolt your failure was in shear. Something to keep in mind before you try comparingtables.



Grade 5 will fail before grade 8. That simple. There are higher grades for this application that should be overkill,10.9 for example.
 

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Lil Pete wrote:
Trainertim77 wrote:
Looking for some insight. My trailer has Grade 8 hardened bolts in the suspension and undercarriage. While in on a trip I hit a bump and one of the bolts snapped in half.


Are you referring to "U-Bolts" or Shackel EyeBolts?


In any event. Grade 8 is better suited than grade 5 for these applicaitons. If it was your U-bolt then the failure was in tension. If it was the Eye Bolt your failure was in shear. Something to keep in mind before you try comparingtables.



Grade 5 will fail before grade 8. That simple. There are higher grades for this application that should be overkill,10.9 for example.
X2...
 

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I think it was just a flawed bolt. A grade 8 1/2" bolt would pick up the whole rig, sling it around, jerk it up and down with a crane and should never break.
 

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The subject of failures in bolts is not an easy one to address through a forum, and I do not represent myself as an expert. It sounds like you have experienced a suspension component mounting failure, and the answer is not to substitute with a lower grade bolt.

There is some misalignment between the imperial and metric system of grades of bolts. For example a grade 8.8 (metric) bolt is not equivalent to a grade 8 (imperial) bolt. In fact a grade 8.8 bolt is more closely aligned with a grade 5 bolt. Thrown into this mix is the stainless bolt which has a different class again. Stainless steel exhibits different characteristics to the more conventional steels, and most "off the shelf" stainless bolts in general terms do not exhibit the same tensile strength or shear strength properties as their conventional counterparts. This is not to suggest in any way that stainless steel is an inferior product, it has it's place and is invaluable in many applications.

You have received some sound advice with respect to correct torque figures for the size and type of bolt in question. It is also good practice to lubricate the bolt thread before "torquing" up, although I concede that many people believe that this will help to induce the nut to work it's way loose. If this is of some concern use a tension washer (eg. spring washer) to correctly maintain the tension in the bolt. A correctly tensioned bolt will help to resist the applied forces both due to the bolt properties and the clamping force (ie. friction) applied between clamped surfaces. Also don't forget that a bolt, nut, and washer is a complete system and all components should be the same grade in a highly stressed situation.

One last thing, if the bolt has been used in the eye of the spring then it is being used as a pivot and this is quite different to the normal clamping application. If it was a spring eye bolt failure this could have simply been a failure due to shock loading, or wear around the shank which would reduce the cross sectional area in the critical stress zone. I think this is classed as a type of fatigue failure.

I guess we could analyse this bolt failure to death, but it will probably be a lot easier to replace with a new grade 8 (or higher grade) bolt!

Good luck with it...
JC
 

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Never !!!!!!!!!!!! use stainless steel bolts in a high load area. Most ss bolts sold commonly are 304,305 or 306 ss, generaly refered to as 18-8, there are harder stainless ( 410 )but they have a higher chance of rusting.18-8 bolts are not as strong as grd 8 or grd 5 bolt.

I would use the grd 8 but nothing less than a grd 5 bolt. The stuff you by in the open bins in hardware stores is usually grd. 2.

I use to tell people whats more important not rusting or not failing.

Jim
 

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Actually the bolt that broke was one underneath the container on his trailer, where the tongue section bolts up to the rear trailer section..He hit a hell of a pot hole earlier in the day and we assume that is what did it, but not sure. Also not sure why it broke in the first place..
Not sure bout where you shop rideandslide, but here in iowa with the farming industry here, most hardware stores and farm/home supplies stores stock all the grades of bolts you could ever want..
 

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farm and fleet and all them mainly sell grade 5 fastners on normal stuff you would not normally need a grade 8 bolt

grade 8 bolts are for exh manifolds things like that sure you can use them on a trailer but its a complete waste of money to do so. or go get a thing of all thread thats about grade 2 lol
 

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Use the stronger grade 8.. My suspicion is that the bolt was defective or damaged by corrosion... a 1/2" grade 8 would hold 10 Goldwings by a single bolt..
 

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Thanks for the help guys, as I suspected, there is a ton of knowledge out here in the forum. I for one think the root cause of the failure was a defective bolt. I agree a quality grade 8 bolt should have handled anything within reason thrown at it.

COME ON SPRING!!!
 

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rideandslidejim wrote:
Never !!!!!!!!!!!! use stainless steel bolts in a high load area. Most ss bolts sold commonly are 304,305 or 306 ss, generaly refered to as 18-8, there are harder stainless ( 410 )but they have a higher chance of rusting.18-8 bolts are not as strong as grd 8 or grd 5 bolt.

I would use the grd 8 but nothing less than a grd 5 bolt. The stuff you by in the open bins in hardware stores is usually grd. 2.

I use to tell people whats more important not rusting or not failing.

Jim
I don't know what your expertise in this area is Jim, Mine is almost nil, just personal experiences and what I read.

The load strength of a typical 18-8, 1/4" to 5/8" Bolt is min. 100,000 to 125,000 respectively. Same or better typical tensile strength as a #5 bolt, again, as most agree, depending on torque specs.

My thought on SS bolts, since this is an Iowa trailer, rust could be an issue. The strength of the SS bolt on a trailer with a few hundred pound load rating, should more than do the trick. This is not what I would think would be considered a "High Load Area"

What is your thoughts?....
 

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Unless I missed sonething here I did not see where the OP mentioned th size of the bolt or what exactly it was doing. Sounds like it was part of the tounge of the trailer.
A pic of the bolt andlocation would be nice. Sounds like perhaps a design flaw in that area. having raced shorttrack stockcars for years I know what it take's to break bolts and can't see that hapenning here.
Wilf
 

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boy this is gettin good where's the popcorn
 

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Whatever you decide be careful with stainless bolts. Example: Ace Hardware carries 2 different grades of stainless. Cheap and more costly. I don't know what the grades are. With the cheaper SS the heads can be stripped easily even when threading into hard wood and they will shear before a proper torque is achieved. Cheap Chinese junk!
 
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