Grade 8 bolts and rust

[Alex Hayley]

How rust resistant are grade 8 bolts when used on the frame?

[Shane]

No more resistant than any other steel based fastener.

[Classic Heartbeat]

The hardness of the bolt does not have anything to do with rust resistance. If you are looking for nuts and bolts with good rust resistance, then you should be looking for coated nuts and bolts. Like zink, cadium, black phosphate, and etc. Zink coated nuts and bolts will give you plenty of rust protection. My personal preferance for the hardness for frame work is grade 5 though. They are not as brittle and offer just a bit more flexabillity. WES

[Longhorn Man]

Wes, I think you and I are the only ones who do that on here.

[Lugnut64052]

Originally Posted by Longhorn Man

Wes, I think you and I are the only ones who do that on here.

Ad me to the list.
I never use anything tougher than grade 5.
I used to work at an outfit that built tow trucks. They did extensive frame stretching, including making huge tow rigs out of semi tractors. They never used anything harder than grade 5 in their frame lengthening operations, or anywhere else on the truck for that matter.

I've never been too impressed with the rust resistance of the zinc coated stuff. Only lasts a year or two for me then it's as rusty as anything else. The black phosphate coatings looks great, but I don't know how long it lasts. Anyone know?

[mr48chev]

The grade or strength of bolt should be in direct relation to where you intend to use it.

Outside of the suspension you probably don't need grade 8.

I used to install a lot of trailer hitches on cars at a dealership in the 70's and they were shipped from the factory with grade 2 bolts.
I'm with Wes and Longhornman in that a good grade 5 with good plating is fine in most cases.

In years of buying fasteners for automotive and industrial use I always felt that I was better off buying a product that the maker put their mark on so you could tell who made it. I have always been a bit shy of grade 5 bolts with no mfg marking.

[cdowns]

if you're worried about rusty bolts either go stainless or paint the plain steel ones

[tcb-1]

black phospate will last longer, but that also depends on the length of time it originally spent in the solution.

hardware that has been well covered and penetrated deeply with black phosphate should withstand years without oxidation. I have never been to keen on zinc coatings. heat and abrasive environments can take that stuff off el quicko......

[PanelDeland]

If you really want rust sesistance you need to use stainlesss.Contrary to popular beleif stainless will rust and must be anti-siezed before installation.I personally use a lot of stainless at work but would only use them as polished on exposed engine fasteners on a truck.
I think the others have steered you right.I also would only use grade 5 on suspension parts.I would much rather have a stretched grade 5 holding it together than a broken grade 8 not.

[tcb-1]

^^ yep, 400 series stainless will and does rust. 300 series will not.

[Skirkpat]

rust (oxidizing) needs to things, oxygen and water, paint it, keep it dry and your bolts will be fine....as far as grade goes. an SAE Grade 5 may be strong enough,but in reality that is an engineering question, refer to a book like a Mark's engineering handbook, or use a comparable factory fastener...or ask A Mechanical Engineer. I have an opinion, but will respectfully not give it.

[rlb67]

Hello all,

I am a mechanical engineer and do stress analysis for sizing bolts periodically. Contrary to some beliefs, grade 8 bolts are far superior to grade 5 bolts in all aspects of stress and strain. Here is good link explaining this. http://www.rockcrawler.com/techrepor...ners/index.asp

[AustinScott]

Originally Posted by rlb67

hello all,

i am a mechanical engineer and do stress analysis for sizing bolts periodically. Contrary to some beliefs, grade 8 bolts are far superior to grade 5 bolts in all aspects of stress and strain. Here is good link explaining this. http://www.rockcrawler.com/techrepor...ners/index.asp

great info, great link!

[texanidiot25]

If you have a GM dealership near you, and have good relations with one, see if the service department will sell you their Grade 8 bolts. Their required to carry standard thread bolts, but all modern GM vehicles use metric. So they have a big inventory of useless bolts... If your lucky you could find a cheap supply of grade 8s

[Alex Hayley]

I checked back in on this thread. Thanks for all the information. I learned a lot more than I asked for.