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Old 09-14-2004, 07:21 PM   #1
daren
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Default Which is stronger Grade 8 or Grade 5 bolts?

Well I was wondering which is stronger or most resistant to a shear force, you know side to side not up and down. Anyway opinions vary, i've heard some say that a Grade 8 bolt is too brittle and that a grade 5 holds up better to a shear force. Just curious I will be needing this info soon. Any engineers or the like care to comment, your reply would be very appreciative.
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Old 09-14-2004, 07:31 PM   #2
crow
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Grade 8 is "stronger" as in tensile strength or force it takes to break it, but when they go the snap.

Grade 5 will flex as it fails and tend distort and stretch and may actually hold together a bit.

I would use Grade 5 in a high shear situation.

my experience and opinion.
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Old 09-14-2004, 07:44 PM   #3
Steve
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

grade 8 is technically stronger but I wouldn't use them in suspension stuff cause like you mentioned they are more brittle
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Old 09-14-2004, 08:27 PM   #4
willowbilly3
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

I am not sure what they are graded but for the best bolts available we always used Caterpillar bolts.
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Old 09-14-2004, 08:29 PM   #5
41ChevyTrucker
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

I didn't know the difference either. Check out this article it is pretty good...

ROCKCRAWLER.com - Grade 5 vs. Grade 8 Fasteners

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Old 09-14-2004, 08:32 PM   #6
demonspeed
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

yea I think crow’s right. grade 8 is stronger but not good for suspension parts. stuff like bodywork you probably on need grade 3 for.
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Old 09-14-2004, 08:34 PM   #7
FrameDragger
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Hmm... Trying to think, I don't think I have ever seen an 8 break... I have broken 5's on an engine hoist before though... Anyone have an experience where an 8 did break? What did it take to break it???
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Old 09-14-2004, 08:53 PM   #8
Deuce Rails
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Check out Carroll Smith's book on fasteners.

At the very least, it will answer all your questions about bolts. At the most, it will save your life.
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Old 09-14-2004, 11:59 PM   #9
enjenjo
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

[ QUOTE ]
yea I think crow’s right. grade 8 is stronger but not good for suspension parts. stuff like bodywork you probably on need grade 3 for.

[/ QUOTE ]

Grade 8 is much better for suspension, period! Read the rock crawler thread again. Want to prove it to yourself, drill two holes in two pieces of bar stock 2 ft long, 3" apart at one end one 3/8", and the other 1/4". put a 3/8" bolt and nut in the larger hole, and a grade 5 1/4" bolt in the other. Hold one bar in a vise, and you can cut the 1/4" bolt in two with one hand, that's shear baby. then try it with a 1/4" grade 8 bolt. You will see the difference.
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Old 09-15-2004, 12:12 AM   #10
crow
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Yes, I have always used Grade 8 on my suspension junk(rockcrawlers). Usually the higher tensile strength is great enough. I have often been confused about the appropriate use. I have always seen Grade 8 on high quality suspension stuff but grade 5 on seat mounts. Someone once explained it to me but I have lost it. I think it has mainly to do with tension vs. shear. Imma read that article closer(again).
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Old 09-15-2004, 12:27 AM   #11
Dan
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

so in a nutshell...for my A coupe I want grade 8 for all suspension/engine/tranny mounts and I can mount the body and seat with grade 5 ????
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Old 09-15-2004, 12:27 AM   #12
redmeat
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

8 is stronger in all aspects....if you doubt me read the article posted by 41chevytruck that article sums it up better then i can...The reason folks think grade 8 shears is because when it goes it is at very high pressure and makes more of a commotion/POP then others

bottom line grade 8 is stronger in tensile and shear strength...period

R E D M E A T
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Old 09-15-2004, 12:32 AM   #13
crow
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

dunno bout that, Dan, as I said it is confusing to me. I use 8 on everything I can. But have seen em go away before(rockcrawling) and they just snapped bigger n shit, no stretch. Where I've seen a 5 completely fuckin choofed outta shape but it was still in the hole. I say 8 everywhere you can afford it.
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Old 09-15-2004, 12:44 AM   #14
Crease
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Grade 8s will yield at approximately 130,000 pi, grade 5s at about 92. The 5 will fail before the 8 if subjected to the same load. However, the grade 8 will fail more catastrophically when it does. Basically, you will have less, if any warning, because of the brittle nature. Personally, I would use grade 8s. The chances of you noticing that your bolt is shearing isn't good. It is possible to get even stronger alloy bolts, but they are typically most common in shoulder bolts. You will want to stay away from stainless in any high impact situation.
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Old 09-15-2004, 01:20 AM   #15
GRADY
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

In our shop, we always use grade 8 bolts on suspension pieces...they come that way from the factory, not that that should be your only reason
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Old 09-15-2004, 01:29 AM   #16
Bass
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Just a little tip...you can buy Grade 8 bolts at your local Tractor Supply by the pound.

I put Grade 8 bolts in just about everything now...and since I ride a Triumph, I've learned to Loctite just about everything as well!
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Old 09-15-2004, 09:40 AM   #17
BoomBoom
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

For what its worth , Sanderson headers says use grade 8 when installing thier headers.
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Old 09-15-2004, 09:56 AM   #18
banzaitoyota
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

I recommend you read "Carroll Smith's Nuts, Bolts and Fasteners and Plumbing Handbook " by Carrol Smith. Also known as SCREW TO WIN.

A plethora of information and how to's INCLUDING riveting and how to PROPERLY make brake lines
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Old 09-15-2004, 10:01 AM   #19
cool57
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

Bolt science web page
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Old 09-15-2004, 10:29 AM   #20
PetT
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

I tried hanging an alternator from one bolt on a big Buick motor once.. kept breaking.. Switched to grade 8 and it still broke. Guess the bottom line is, bolts break when used improperly.
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Old 09-15-2004, 10:31 AM   #21
Rand Man
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Default Re: Which is stronger Grade 8 or Grade 5 bolts?

I don't have time to write an essay on fasteners today. Ask the automotive bolt experts at www.arp-bolts.com. This subject is too important to go on hearsay.

I learned the difference in shear force as kid in the hay field. The old square bailers had a shear pin on the flywheel. It was designed to break if a stick or something jammed-up the works. One day I ran out of the regular low grade bolts and replaced it with one with a "bunch of marks" on the head. Later on when the PTO drive shaft twisted in two, guess who was in big trouble.
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