GRADE 5 or GRADE 8...that is the question

wished you would've thought of this before. hopefully the f-100 will hold together huh? j/k
love it man. driving the **** out of it. everything is working well.

 

Guys if you need to have one source for really great info look no further than my company's fastener info pages. Kimball Midwest is a national supplier for shop supply. Our fasteners and most of our inventory is American made stuff. I can help you if you decide to order anything from them. Hamb'ers get a discount. The link to the fastener info is..... http://www.kimballmidwest.com/Catalog/TechnicalInfo.aspx?p=2599

 

Hahaha, while it's true, I did turn many wrenches and bloodied many knuckles (I'm a clutz), the suspension and ch***is work was ElPolacko and gang.....

You'll be fine! Glad to hear it went to a good place.

 

Seriously, man, quit it already. You aren't making yourself look any smarter. Leave the replies to the people with an engineering background.

 

Kimball Midwest stuff freakin kicks ***.
Thier Pro-Max paint compares to Eastwood stuff at a fraction of the cost. We have used them for Years now.

Nice cheap first aid kits, too.

 

or the guys who like Zinc DiChromate gold.

 

Ziiiing!

 

Im a firm believer in grade 8 NF for suspension, just for piece of mind, I know it may sound stupid, but I use grade 5 for bolting wood structures together.

 

just wanted to say this thread is/has been a test of wits, anybody for any reason that could justify using grade 5 hardware instead of grade 8 must ride the "short bus!" bet they use grade 5 on the short bus suspension?

 

Just a quick comment, reading these 'discussions' about bolt grades is like watching a car accident about to happen - you can see what's going to happen, but you are powerless to stop the carnage.

People conflate 'grade' with 'quality' as if a higher 'grade' number means better quality. That is simply not the case. Bolt grading is a way to describe the properties of a particular bolt. In a child's swing set, you want a grade 2 bolt. In most automotive clamping application, you probably want grade 5. Grade 8 has its uses, but it is not a higher quality bolt, it's just a bolt with higher tensile (and other) strength. If you think you need 180,000 pounds of tensile strength, you are better off getting a larger grade 5 bolt instead of resorting to a grade 8 bolt.

As I understand it, bolt failure is more often traced to a bolt losing its tightness, thereby leaving the bolt to experience shear forces (which I think are 60% of tensile force), and the shock forces of the moving parts, when it should have been living in its tensile forces. Grade 8 bolts have less of an elastic range (where it is imparting a clamping force) than grade 5 bolts. Expansion and contraction of the parts being clamped, deformation of a low-grade washer under the bolt, and especially improper bolt tightening technique will all contribute to a bolt losing its clamping force.

I have heard of a very successful race car shop that barred the use of grade 8 bolts anywhere on the ch***is. Good luck to all.
Paul

 

Almost made it to 8 years! Yes I did read the whole thread..

 

I break my stuff down into two cl***ifications. Shear or break points or low stress points.

Grade 5 for low stress points not to exceed 50 ft lbs
So attaching hinges, body panels, intake manifolds and accessories.
Grade 8 for suspension, steering, engine, trans, axle etc.

I laugh when I see a car put together with stainless all over it to "look" good. Seen way too many stainless fasteners fail in my time.

 

Never mind my answer. I have decided that I am boycotting any thread older than one year.

 

So nothing but new bolts for you

 

LOL yep can't build anything trad because my bolts all have to have new threads.

 

i prefer grade 5 where i'm concerned about high shear forces and grade 8 and better washers and nuts when it's high clamping forces so i tend to agree with the above comment.

 

Well for a high shear load think of the 1/2-20 grade 8's that hold your 9" ring gears in place..Healthy HP and big tire and prepped track...They do a pretty good job at shear and the resulting shock loads..I used L9's, probably even stronger ones now..Worst in my opinion but maybe I just a worry wort is the coil over mounting, one bolt in single shear with usually a spacer involved...I know, a million out there......

 

I've been replacing everything with stainless because I live in the rust belt. Is this a good or bad thing?

 

Here's a good bit of interesting info. on Henry Ford and the bolts he used.
http://www.jalopyjournal.com/forum/...y-ford-bolts-nuts-and-washers-show-me.614962/

 

STOP
Replacing everything with stainless is a very bad idea. Stainless bolts have no where near the strength characteristics required for automotive safety. Plus, they "gall" steel and are soft. You must read this explanation.
http://www.ebay.com/gds/Stainless-Bolts-Usually-very-weak-/10000000001623345/g.html

 

I use grade 8 for mostly everything.

what about exhaust manifold bolts? last time I had my manifolds off my 390FE, almost all the bolts broke. I replaced with grade 8 bolts and used anti-sieze. been on there for 2 yrs and all rusty looking. wonder if they will come out easy or not. im not gonna check until I have to.

 

I am the old HAMB Metallurgist, I do know what I am talking about (so do several others in this thread form any years ago). I highlighted your statement. You are so wrong. Grade 8 has MORE elastic deformation range than grade 5. It has to, because it has higher yield strength. You have misunderstanding of basic material properties and tensile testing.

Grade 8 bolts do tend be higher quality material, and they are heat treated which gives them their mechanical properties, along with post-heat treat rolled threads to improve fatigue cracking resistance. Grade 5 are improved over grade 2, but both gain their strength by the cold working process, during the cold heading and thread rolling operation to make the bolt. Using a Grade 8 bolt at less than its maximum strength is just fine, such as replacing a Grade 5. It still results in a clamping force on the joint. Clamping force is a result of stretching of the bolt, which is a function of the elastic modulus. Grade 2, 5 or 8 all have essentially the same elastic modulus. What they have different is the yield strength, and ductility once they exceed the yield. I won't get too technical with work hardening exponent once past yield, but for general discussion, ductility as percent elongation is highest in Grade 2, then Grade 5 and least in Grade 8. This DOES NOT mean grade 8 snaps. It simply means that grade 8 will stretch and neck down less once it has reached plastic deformation stage. It will still stretch and bend before final stage overload fracture.

 

@38Chevy454 i have noticed that a grade 8 bolt seams to resist corrosion better than a grade 5. i use them on plow frames and after years of abuse come right apart. am i imagining it?

 

******
A lot of the older threads do take on a "moldy" vibe, but not when it comes to discussions about fasteners, especially in this day and age where the big nut/bolt suppliers (local) are closing up. I won't even say how dismal the situation is with the way the big box stores and their fastener depts have become.
With places like the HAMB taking on new members daily; automotive fastener discussions should be given a "sticky" designation. Would be especially valuable for the younger guys that may not know that all bolts are not created equal.
Some of the better stocked "hardware" stores still display mfgs boxes full of fasteners, this has value to me because you can at least see the country of origin on the box.
The ones that I'm suspect of, are those nice and shiny zinc chromate "washed" grade 8 fasteners that are Made in China. Granted, few of us drive formula one cars, but you won't see any of those on any of my cars' suspensions.
Price should not be the central criteria when buying critical fasteners, but in this internet driven society that's the reality of it.

 

I bet a lot of people don't even know that there is such a thing as grade 8 flat and lockwashers, not to mention grade 8 self locking nuts.

 

I do like lock nuts on a part that doesn't get adjusted or removed very often. Something of mention is that I don't use nylocs on suspension pieces at all. I have not had good luck with them and once you loosen it you should replace it. I do like the self locking fine thread nuts on a part that is not going to be removed or adjusted. The ones with the little dimple on the flat are my favorites.

Here is another little known fact, you can also buy flange nuts in grade 8. A properly torqued flange nut will not loosen on you as long as the flange has something to seat against.

No matter the grade of the bolt, it should be torqued and not just gorilla-ed.

 

This is probably due to the chromate coating more than the zinc plating. Grade 8 tend to be gold chromate, which is a better than the clear that is common on Grade 2 and 5. The slightly higher alloy content would have small effect, the main corrosion resistance is the plating and the chromate. The gold chromate active part is hexavalent chromium, and clear chromate is trivalent chromium. Hex chromium is getting harder to get, since it is carcinogenic.

Good point, for maximum joint strength the washers and nuts should match the bolt.

More general bolt theory: torque is actually a very bad indicator of total stretch in the bolt. This is why high end race engine builds will use a rod bolt stretch gage. The bolted joint is intended to provide a clamping force. This clamping is actually provided by the bolt stretching, think of the bolt as a very stiff spring. Using torque has a lot of error since you have the friction that is result of the clamping force. But too many variables with the friction vs stretch correlation. Torque is used because it is easy and works for most applications. This is also why the surface finish and any lube on the threads is an important factor.

 

Be wary of using the pretty electroplated fasteners for high stress applications. Hydrogen embrittlement has a causal link with electroplating.