What grade of bolt to use on suspension and why?

If you are not drag racing or street dancing, there is no reason you should EVER break a grade 8 bolt in your suspension. If you break a grade 8 bolt, something is wrong. Either you need a larger diameter fastener (not likely), or your suspension is binding.
There was my opinion, here is your fact for the day:
NHRA Pro-Stock cars use 1/2" AN bolts on each end of the 4 link bars. This is a military grade aircraft bolt, but it's only 1/2". These are cars that make well in excess of 1000 horsepower and run well below 7-second 1/4 mile times.

 

I just put a 1/4-28 x2 Grade 8 Rockford Brand Hex head bolt in my vise and gave it a few whacks with a hammer. It bent to 90 degrees before it snapped. Did the same with a 1/4-20 x 2 in. long Hex head grade 5 bolt and did the same thing. It bend to 90 degrees but didn't break. I think it would be great if a metallurgist on HAMB would clearly
explain the relationship between a bolt's application in a vehicle and it's shear strength, tensile strength and impact strength. No doubt there is a big difference between the load placed on a bolt during the sudden impact (of an accident) or a gradual continuous or intermittedent load. Hence different bolts for different applications. When I took the front suspension of my 51 merc apart (inlcuding backing plate bolts)I am sure the bolts were NOT grade 8. I have the feeling that Henry Ford would rather use a bigger dia. Grade 5 bolt than the more costly Grade 8.

 

Whatever you do, buy from a quality US source.
Grainger, MSC, McMaster, or ARP. The great Smokey belived in ARP and he knew his shit.

Frank

 

It would seem logical that the type of bolt used would be dependent upon the type of FORCES it is MOST OFTEN subjected to in a particular application. For example: body mount bolts would not NORMALLY be subjected to the same forces as connecting rod bolts. I wonder if it's a trade off between tensile strength, shear strength, torsional strength, ductile strength and impact strength when engineers specify a specific bolt for a particular application. When I took apart the suspension on my 51 Merc I am quite sure Henry Ford didn't use Grade 8 bolts and nuts. I bet he just used less expensive (and bigger dia.) grade 5 bolts figuring that under normal conditions (loads), they would do the job.

 

This brings ups another good question: When to use fine vs. coarse threads?

 

What about stainless bolts?

 

Please click this link and you will find some of your answer, and a simple search if you are truly interested would be helpfull.

http://www.rockcrawler.com/techreports/fasteners/index.asp

 

I'd use Grade 8. Please make sure you buy a quality fastener. Check out www.kimballmidwest.com. We carry American made bolts made by Lake Erie Capscrew. If you need 'em I'll help you and give you a HAMB'ers discount to boot. There is good info on the website about torque and yeild strength etc.

 

I don't know that much on stainless hardware but the stuff you get from hardware stores is usually low grade and weaker than a grade 5. I think it has to do with carbon percentages and not being able to heat treat it. Plus you have to mess with anti-seize because of gaulling. It's a pain I'd only use stainless for certain show parts (not suspension) because they have a nice finish. I do know that ARP and I think its Totally Stainless have high end stainless fastners that are quite strong.

 

I took the hint and bought grade 8 bolts from a specialty supply marine and tractor place. The local home stores and ACE do not carry anything longer than 6 inches.

You guys have been a great help and education, thank you very much.
I am puzzled by one thing though? Everyone here has said grade 8 and provided the facts to back it up, so why then would Fatman tell me to use grade 5. Surely these guys have access to the same information.
Do I need to worry about the rest of this setup from them? Again I didnt put this in the previous owner had it welded in, I am just trying to do it right with what I was given when I bought the truck.

 

Not sure why he would say that. There are misconceptions on various fastners. For that matter on many subjects. That's why the internet is such a great tool. You can research for yourself.

 

Like has been said before, the guy from Fatman is a fucking idiot.
If the suspension is well designed ( I'm not familiar with Fatman ) there should be fuck all sear load on any bolts. If it has crush tubes or even better, double shear design, the loads become more tensile than shear.

Just cause a company has a "famous" name doesn't mean they are any good.

Post some photos. If there are problems, I'm sure someone here will spot 'em.

 

Thank you so much for sharing!) Me and my dad love your forum))

 

Look at OEM bolt grades and where they are used. From what I've seen, anything that attaches something to the spindle or steering knuckle is a grade-8. Higher torques go with higher-grade hardware. Take great pains to make sure your hardware will never loosen up, like using safety wire, lock washers, lock nuts and locking compounds. Loose hardware is probably more responsible for something breaking under stress.

 

I stopped buying axles for the choppers i was building because i was paying $80 each when i could go to fastenal and get a grade 8 bolt for less than half. The shear rating on it was so freaking high that i was never concerned. Should've seen the looks on their faces when you say " i need a 1"x16" grade 8 bolt and poly locknut please

 

my off topic drag car has a well known chassis company back half kit in it it came with grade five hardware when i called on it they told me it was a maintenance item and they would wear instead of the mounts

 

Grade 8, because it makes it look like I know what I’m doing

 

I use the factory bolts on suspension when possible.
I have seen grade 5 bolts in roll cage applications mandated by rules.
Used 8 on most non stock suspension applications. I say most cause now I’m wondering what the grade all the chrome bolts were that came with the axles and shackles I used.

The M2 originally had the strut rod. Then the aftermarket guys made the cleaner strutless lower arm.
The extra stress on the lower arm bolt was not intended from its original design.
I bet the factory bolt never failed with the strut in use.

 

One of the problems I have encountered is finding the perfect length in any grade

 

This is the 2nd thread that new member, SamathaHumphreys has resurrected from the dead, 12 yrs. and 8 yrs., and everyone just jumps right in to keep it going. Interesting. Lol! I guess I am guilty as well. Sorry.

 

From real experience. My tractor PTO drives the brush hog. It has a 5/16" shear bolt in the shaft to prevent major damage if you hit something. Put in a grade 5, I can't make it far before it shears off. Put in a grade 8, unless I hit something big, it won't shear off like the grade 5's do.
I use grade 8 in almost everything, they don't seem to rust as fast as the grade 5.

 

I'm not a engineer and don't profess to know it all but I have helped install a few of Bretts Mustang II front suspensions for a few of the street rodders I know and used the parts from Fatman's, I don't know of any problems with the bolts supplied with the kits. HRP

 

From my experience if you take a three cornered file and it just glides across a “supposed “ G-8 fastener it is only case hardened, and not hardened throughout. If you cut a true G-8 bolt with a hacksaw it will have a gummy feeling.
Being retired I don’t have access to a Rockwell hardness tester but if I did I’d expect a reading on the C scale of 25-34 for a Grade 5 and 33-39 for a Grade 8.
Anybody have a Grade 8 from Fastenal and a Rockwell tester they could use?
If a bolt was made by Ubrako or Holo-Chrome you can expect quality.

 

Now I feel like a fool.....lol

 

I think everyone gets caught out like this at least once, probably more often...........

 

Fordors listed a couple of quality fastener manufacturers, to which can be added ARP of course, and various others.

However don't assume that bolts supplied by a major fastener distributor to be made in the USA. They generally buy fasteners from whoever is cheapest that week and certifies that the bolts meet the standards. From whatever country that might be.

I'm sure he wasn't implying to use a bolt that's been destructively tested, but a bolt that's scratched with a file will lose a lot of its strength.

 

I've always heard the "grade 5 will bend before braking, and grade 8 will break sooner", but of all the bolts I've broken, most of them have been grade 5.

So, I just use grade 8 for just about everything, unless it really isn't subjected to any major forces. Probably overkill in many situations, but that doesn't bother me.

 

Destructively tested would mean pulled to its tensile strength limit, but a small nick on the head of a bolt wouldn’t hurt anything. Let’s say you buy a bag of Grade 8’s at the local hardware or big box store, or maybe even Fastenal. Take them home and check one with a file, if they prove to be case hardened you don’t want them.

 

You've got a Tractor Supply there in Kingsland. Walk in and buy them in bulk. Way cheaper than Fastenal or any of the big box stores. Yeah, I know they're made in China but I've never had one fail yet. I generally buy a lot of the same sizes in both Grades 5 and 8 so I don't have to go running somewhere trying to find the right size bolt.

 

If you have something that you need a specific length for and can't find what you need, look at AN bolts. An AN-5 means a 5/16 diameter. An AN-6 is a 6/16 which is 3/8 diameter. I believe lengths are stepped by 1/8 '' which should pretty well cover any need.
https://www.aircraftspruce.com/catalog/stpages/anbolts.php

One thing to consider is the size of the bolt when making a decision. A 1/2" bolt is a serious piece of hardware and may indeed work well as a sacrificial lamb while staying intact. If I was dealing with some 1/4" bolts working with each other I think I would view things differently but 1/2 inch anywhere on a car is a heck of a bolt.