grade 5 vs grade 8 bolts(chassis/suspen)

[crazy longhorn]

This post is a spin from another post that was about stainless fasteners. I am working with plain steel fasteners, so I figured to start a new post would be better than "hyjacking" a post per say. I have heard it said by several guys that grade 8 is not good on chassis , or suspension parts.....I am no engineer, but if you crawl under your truck, & check the markings on the factory bolts holding the front crossmember.....you will find they are grade 8! The eye bolts on the springs (factory leaf truck), also have grade 8 bolts! The bolts holding the steering box are grade 8, as well as the idler arm(factory). there has been a lot of discussion on 5 vs 8 on the fasteners.....i tend to go a bit overkill on some things, but have always felt that a grade 8 was the way to fly on suspension pcs. the U bolts will be a softer grade, I guess so that they can "wrap" the axle properly? the last Bell tech spring hanger kit I installed (90 GMC shortbed), had grade 8 fasteners, to mount the hanger to the frame I have followed this with every pc that has been removed/ replaced on my chassis. I run 7/16 grade 8 hardware, with pinchlock nuts on my spring hangers, trans crossmember, & carrrier crossmember.....both crossmembers are custom pcs.I feel that the fit on the bolt in the hole is important.....no slop, they were drilled to fit tight enough that a few had to be tapped in with a hammer. I have yet to have a grade 8 bolt come loose, or break, on the bottom side of the truck. crazyL

[Bobalouie]

I look at it this way...If you are going to be bolting something together where the bolt is going to be loaded in tension or compression (for example a tranny x member, bed to frame bolts, cab mounts), Grade 8 is fine, although not needed. If you are loading the bolt in shear (for example shocks, leaf springs front x member on a 2wd), you would be better off with grade 5. If you want to use Grade 8 on a shear loaded part, you would want to make sure that the load is not significant.

[Longhorn Man]

Al, you may be refering to my mentioning this in the SS bolt thread.
While I stand by my opinion...based on facts, I had never bothered to look at what was under there from the factory.
Personally, i'll still use grade 5 on the chassis and 8 where it might actually be needed, but I guess you have a very good argument here.

[tom hand]

http://www.rockcrawler.com/techrepor...ners/index.asp

[crazy longhorn]

That is a very good thread Tom the article explains tension & shear loads pretty well, as well as bolt strenghts. while I will agree that some of the grade 8 fasteners are a little overkill,but shouldnt cause any trouble. I see the factory has used them on these old trucks in some places .......my guess is that there could be a good reason for that? As far as factory, the leafs & front crossmember are grade 8(my front crossmember has never been off the frame). crazyL

[Sweet72]

In reference to the stainless hardware, the commonly available stainless that you can buy at your hardware store and home center is far too soft for chassis/suspension. I've replaced all gr.8 and gr.5 bolts on the '72 with new hardware With 8 & 5 respectively.

[wxman1]

Bobalouie said: If you want to use Grade 8 on a shear loaded part, you would want to make sure that the load is not significant.

What would be you reasoning for saying this, in light of the info presented in the article ?

Jim
Mt Juliet

[Tx Firefighter]

I was taught in A&P school years ago, that the FAA required a grade 8 bolt or better in any situation where a bolt was replacing a rivet on any aircraft. No diffrentiation was made between shear or tensile loads. I figure the FAA and all the aircraft engineers have researched it thoroughly, concluding that a grade 8 was appropriate for any load condition, so I go with them on the matter.

Yes, a grade 5 bolt will deform when failing, and a grade 8 will fail catostrophicaly, but a grade 8 bolt will fail under higher force than any grade 5, so arguing about the sudden failure of grade 8 is pointless. The grade 5 would have long been failed by the time the grade 8 does.

[Fred T]

First, from an engineering standpoint, I agree with the article from Rockcrawler. And, as I stated in the other thread, you cannot go wrong if you replace your fasteners with the same grade as the manufacturer used. If you want to use grade 8 for everything, it is fine, it's just not what I will do in most cases. A matter of preference and not worthy of any arguments.

I was taught in A&P school years ago, that the FAA required a grade 8 bolt or better in any situation where a bolt was replacing a rivet on any aircraft. No diffrentiation was made between shear or tensile loads. I figure the FAA and all the aircraft engineers have researched it thoroughly, concluding that a grade 8 was appropriate for any load condition, so I go with them on the matter.

I am going to have to ask about that one. It goes against how we design structure. First rule is only replace a rivet with a rivet, and never mix a bolt into a rivet pattern. When the shop requests replacement of a rivet with a bolt for installation purposes, we call out a low strength bolt and place a note on the drawing requiring the use of substitute bolts to be for the entire pattern.

[68LSS1]

:p :p No comment.

[Tx Firefighter]

Originally Posted by Fred T

I am going to have to ask about that one. It goes against how we design structure. First rule is only replace a rivet with a rivet, and never mix a bolt into a rivet pattern. When the shop requests replacement of a rivet with a bolt for installation purposes, we call out a low strength bolt and place a note on the drawing requiring the use of substitute bolts to be for the entire pattern.

Look in your FAA AC 43-13 book. It's the standard book by which all aircraft repair or modification must comply. Every Airframe and Powerplant mechanic has to be studied on this manual and pass three tests on it, a written, an oral, and a practical test on it before becoming licensed. It states that a rivet may be replaced by a like sized bolt as long as it's grade 8 or higher.

[Sweet72]

Originally Posted by 68LSS1

:p :p No comment.

Aw come on 68LSS1, surely you have something to add

[Bobalouie]

wxman1 said "What would be you reasoning for saying this, in light of the info presented in the article ?"

Mainly, my thinking was, because when grade 8 fasteners fail, they fail castastrophically. They pretty much shatter. I also had not read the article before I posted, but now my mind is changed.

[chickenwing]

Tom Hand, Outstanding article. Thanks for sharing.

[68LSS1]

Originally Posted by Sweet72

Aw come on 68LSS1, surely you have something to add

Oh ok. My stainless steel trailing arm bolts are stronger than grade 8. But that's what's great about this board. If you are not learning new stuff than you probably don't need to be on it. Tx, I'm going to have to dig out my AC4313 and will take a look at the SRM (Structural Repair Manual) tonight at work and see what Raytheon says on the subject. That's been too long ago.

[Dave Reed]

68LSS1, you work at Raytheon? My brother works there. An EE, last time I asked he was debugging code for the Patriot.

Not to change the subject, but I was told by an engineer, (my boss) that SS is far more brittle than steel. I can't argue with you on that, but anyone care to enlighten us on that?

[Sweet72]

I'm no metallugist or engineer, but I know that stainless can be alloyed, tempered and hardened for almost any application. However, finding stainless hardware of the correct grade for a specific application can be difficult for those of us who lack the resources. Making a blanket statement that stainless is more brittle than steel is just silly.
I chose to install zinc plated hardware of the same grade as was installed by the GM assembly plant. It just made it easier for me.