So, i broke a Grade 8 bolt........

Took my roadster out for a cruise tonite and a half mile from my house bang, i'm draggin the left side of the frame down the street......Suicide frontend with the spring perches mounted through the wishbones........The 1/2" grade 8 bolt holding it snapped......Question... Would i be better off with a grade 5?....Are grade 8 easier to shear than the 5.....Someone mention that a 5 might be a little more flexible and not prone to shearing.....What do you guys think?

 

tube axle or I beam?

 

Nix on the gr 5- Id say the grade 8 is definitely the one ya want to replace it. Check and be sure the quality of your bolts there are some inferior hardware being sold nowadays...
I would also recommend a second opinion on design/geometry....is the bolt in question one that was in service a long while?

 

Beam

 

Don't go to a grade 5, a grade 8 is better in every way. If you broke a grade 8, it needs to be bigger, end of story. (Unless the bolt had some kind of a flaw.) There are some really crappy bolts out there nowadays, made in China. Don't take someone's word that it's a grade 8, it has to have the 5 marks on the head. The best grade 8 bolts you can buy are available at Caterpillar dealers.

 

I've had the car 3 years and who knows how long it was in there before that

 

How about posting some pix. for some opions of the set-up. Maybe someone can offer better help then. I'd also like to see it as I have my perches in my bones as well, I'd like to not have it happen to me.

 

First thing in the morning i'll get some pics....

 

had that bolt been welded on? i would most certainly check over that setup.......and when you fix one side, check the other...

some of the suspension gurus here could probably help you a lot more with pics..

check this out...

http://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm


edit: huh? ....never heard of a grade 9 bolt...

http://www.almabolt.com/pages/catalog/bolts/commonheadmarkings.htm

 

I'd like to see the broken end of the bolt, could have been cracked for a long time. A fresh break will be shinny all the way through, if part of the broken surface shows discoloration, that area was cracked for a while, the darker the discoloration, the longer it was cracked. I'm betting its been cracked for a while, if not, you need to find whatever broke the grade 8 bolt and correct that problem. Gene

 

Well now you know why they call it a SUICIDE front end. From what I've heard great 8 are stronger under pulling forces, while grade 5 are stronger under a shearing force. Honestly I would look into changing your mounting setup all together. I've got a suicide setup on my T-bucket, but I made a spring mount that goes all the way around the bones, and is welded solid. I'd post some pics, but I don't have any on my computer right now. Do a search on the H.A.M.B. for suicide front ends, there's a few guys on here runing similar setups, (it's where I got the idea!).

 

I'll jump in here with what little I know from the race car days. Grade 8s are strong-- Grade 5s are tough . If that makes any sense. Also 8s can be brittle, and should be used in the right shear conditions . AND as above said CHINA CRAP is going to get someone killed.

 

word ...

 

Was the bolt that broke chromed? There is such a thing called hydrogen inbritlement that happens when steel over I believe a Rockwell 60 hardness is chromed. After chroming something this hard, it needs to be put in an oven at a set degree, for a set amount of time, and within a set amount of time from coming out of the chrome tank.

Of course none of this matters to you if the bolt wasn't chromed. Good Luck

 

Check the mount for sharp edges aswell. Grade 8's are hard, there is a compromise with harness/britleness. did it break the head right off? . Id stick to the grade 8, but make sure it is a nice fit, you dont want that bolt bouncing around inside a sloppy hole.

 

Fastenal sells what they claim to be a grade nine bolt, as strong as grade eight with a higher shear stregnth. I worked there for about six months and everyone who bought them loved them, but beware, they are pretty spendy.

Nate

 

http://www.engineershandbook.com/Tables/boltgrades.htm


They make bolts stronger than grade 8. Technically, the SAE doesnt call them Grade 9's, but some people who make them call them what they want, so you know they are stronger than Grade 8. I don't know if this is marketing ploy or what.

As for the brittle/hard as glass argument, its BS. ASTM A490's are stronger than grade 8, and designed for structural purposes (like ARP bolts). They arent more brittle, in fact, lower grades will bend and brake before higher grades begin to even stretch or bend.

Eaxmple of tensiles:
Grade 8 = 150,000 psi
Metric class 10.9 =145,000 psi
What's considered Grade 9= 180,000 psi
Metric class 12.9 = 174,000 psi
typical socket head cap screw (allen) = 170,000 psi

For piece of mind if you think the Grade 8's aren't enough you could run F911 bolts. I know Polyperformance, and Kartek carry them.

 

Another thing to consider is that if a bolt is not tightened properly and is allowed to work back and forth even by the slightest degree, it will cause fatigue and eventual failure.

Without seeing the actual installation, it sounds as if the at least a portion of the problem is the way that the joint was bolted together. Are there sleeves welded into the wishbones where the bolts pass through? If not, it would be nearly impossible to tighten the bolts tight enough to provide enough clamping force to prevent the perch mount from moving slightly under load.

When the bolt is used in tension, it's main purpose is to clamp the two pieces together inducing enough friction so as not to allow the two pieces to move. If the clamping force is not great enough, the two pieces will be allowed to move in relation to each other putting undue stress into the bolt causing eventual failure.

Likewise, if the material used for the perch mount is not thick enough or the holes that the bolts pass through are too large for the bolt size, the mount would be allowed to flex and move, again putting more stress on the bolt than it was designed for causing it to eventually fail.

If the design of the mount puts the bolt into a single shear situation AND the clamping force is not sufficiant to prevent the two parts from moving relative to each other or the mount is made of insuficiant material, the bolt has no hope of surviving the stresses put on it no matter what grade the bolt is. Ok, so there may be some wizz-bang aerospace bolt that can survive under those conditions but I think you see my point.

You can see that it may not be the bolts fault, it could very well be a design flaw.

 

The F911 style bolt is MUCH better than a grade 8, assuming that there are no geometry or embrittlement issues, as previously mentioned. Make sure the spot the bolt goes thru isn't holding water. Seals-it makes a neat seal for bolts that can keep water from getting in next to the shank.

If all else fails (no pun intended), there are NAS shear bolts available that are designed to be side loaded. Try Coast Fabrication, but make sure the credit card is warmed up, cause they'll redline the sucker...

 

Loogy,damn you be smart.
Dat be the an-sir.

 

PM me a measurment and if I have any supertanium bolts (used on Indy cars) the correct length I will send em to you. They are THE strongest bolts you can get period. I promise you wont break a 1/2 supertanium bolt

Roy Caruthers
www.exilesindy.com

 

Do you know Jeff Haywood at coast?

 

Supertanium used to be the strongest fastener made & had absolute quality when it was marketed by Premier Industries-- however the trademark was sold to a competitor ( not a really high class one at that) Lawson I think was who bought the name & I would question if they are still as good as they were a few years back.
That said , if Supertanium is even half what it was when Premier designed & marketed it it's still a darn good bolt.
I'm not prejudiced just well informed , I sold supertanium for 20 years.

 

Okay, a coupla pics.....The first shows the set-up....I know that the shackles ideally should be at a 45 degree angle.....Mine might be 20. That's the way it was put together and it's been that way for years so i don't know if that would have anything to do with it...



The next shows the piece that was in the spring perch boss.....It was a clean break where the perch bolts to the inside of the bone with no shininess.....What's fucked up is that's all the threads that was holding it together Maybe 2-3, and based on that you know that there is no shoulder to ride on....Probably threaded all the way to the head...Can't tell because the other piece waved bye bye and i haven't pulled the other side out yet....Figure i'll do one at a time so i don't have to spread the spring.....I can get at least a 3/4" longer bolt in there with the right shoulder.......I'm gonna guess the lack of shoulder on the bolt and the shortness of it was the problem....Oh, and i think i would have liked to have seen fine threads

 

That's some life support!

 

I think I would reconsider the geometry of this set up. It looks to me like there maybe a tremendous amount of stress being placed on the bolt and from all directions. Does the spring eye hit the frame on full compression? If you can, get us a wider photo of the front end. Another suggestion, you may want to take the other side a part while your working on it. Do a good inspection and familiarize yourself on how it was put together. You may find clues as to how this side broke. This is dangerous my friend.

 

Great science here but if one broken bolt puts the frame on the ground theres too much weight resting on the bolt. Stand back and look at the basic design and make the necessary alterations. Just my opinion.. ...Bob

 

2-3 threads is scary..

hey, i wanna say something...

most guys are too proud to post something that went wrong on their hot rod.....with this being on the hamb now, you may have just saved someone's life.......

here are some pics i've saved from the hamb....

 

few more....

what about ordering some perch pin bolts and using a nut on the outside instead of a bolt threaded in bung......

there's one in particular that i'm looking for.....it's a cut out pc that is slid down the wishbone and welded in place.......very nicely done and strong...it's a tech on here somewhere...

 

here's your strong solution...

in the tech archive do a search for "perch"

http://www.jalopyjournal.com/forum/showthread.php?t=103232&highlight=perch