That bolt appears to be a SAE grade 8 bolt. The triangle is the manufacturers marking. I have a guid to bolts at work, with marking from the major bolt makers

That is a graded bolt. That is a grade 8 SAE.

Metric bolts have the grade stamped numerically in the head. Standard bolt grades are denoted by those radial lines.

Gotcha.
Appropriate bolt?

Craig,

First, there's no way to tell whether it's a real Grade 8 or a cheap counterfeit, as these bolts have been faked overseas for many years now. Even a reputable supplier may have difficulty guaranteeing the bolt's origin if they don't have the original manufacturer's lot numbers.

Anyway, no, I don't think Grade 8 is enough for an application like that. I would spend the money and get a 12.9, (SAE Grade 8 is roughly equivalent to metric property class 10.9) or something aerospace grade. It's going to be freaking expensive, but worth it. Use one of the aircraft suppliers, or a specialty house.

Do you have Carroll Smiths Nuts, Bolts, Plumbing and Fasteners Handbook? It's great.

IF i think back to highschool science class:

the higher the grade might not be a better choice for the aplication,

i might be wrong but the higher the grade was more tensile strenght but less shear strength?!

i want someone to verify this first im probubly wrong

what is scary is that Mr Greg Fordahl (who i have heard nothing but good things about) dosent know the grade markings for an SAE bolt?!?!

maybe i read that wrong?

Hmmmm, I had a feeling that it was Fordhal. Is there a reason they installed them upside down???

Jeff

John,

I think I agree with Pelican air-cool-me. It seems the failure was from repeated bending of the bolt. Of course it was incorrectly installed up side down according to the manufacturers instructions. I think a harder bolt would be more prone to this failure than a softer one even though it can sustain higher clamping force.

Chuck, isn’t six marks for SAE grade-6 and eight for SAE Grade-8? What is the relation between 8.8, 10.5, 12.9 and SAE?

The first time I saw this set-up with that drop, I said to myself “That looks like a failure waiting to happen.” I think this is more than just a hardware failure or incorrect installation problem – design problem comes to mind.
What also concerns me is the relatively small diameter of the outer cylindrical parts. It seems to me the combined clamping force and the lateral (bending) forces can exceed the deformation limits, particularly if it is just mild steel.

This is not an area of professional expertise for me but I do stay in Holiday Inns. Please correct me.

Best,
Grady

Craig,

Looking at your most recent photos showing the bolt "reassembled," I can see considerable wear on the bolt shank, about an inch above the head. That's further proof that this bolt was "working" or wobbling while it was installed and that bolt preload, if there ever was any, was lost. Another observation from your earlier photos: the fatigue cracks progressed through a large percentage of the bolt before final fracture which suggests that the bolt was not particularly highly loaded while in service.

I agree with Greg Fordahl and others on some of this: it really doesn't (or shouldn't) matter which way the bolt was installed. Once the bolt loses tension, there are several locations along the bolt where (unwanted) bending forces will occur. Of course, given similar bending loads, the most highly stressed area, and hence most failure-prone, is where the threads are located. It's very likely that if the bolt had been put in with the threads down, you would have suffered the same mishap.

I also agree that to minimize the threaded length is a good idea, but that can sometimes be easier said than done, because threaded length is not always available in the full array of choices that you may desire. I wouldn't trust that simply shortening the theaded length is going to get you (and me!) out of trouble. As you can see from the photos I posted earlier, fatigue happens (if it can). It's possible to fatigue the non-threaded portion of the bolt as well. You've got to keep this thing out of the bending mode. But it would certainly be nice to get the transition from the unthreaded to the threaded portion of the bolt shank away from the point of maximum bending moment. But geez, the design should not be so marginal that its survival is dependent on the threaded length of the bolt.

A higher grade bolt would also improve fatigue life, but it appears you have a Grade 8, which for most automotive applications is more than fine. Again, it's scary to think that the design should be so sensitive that the difference between a Grade 8 and Grade 12.9 is going to save the day.

Short of doing a full design analysis, I think this would be the best approach: replace the bolts (and nuts), use the highest grade you can get, get some with shorter threaded length if you can, and torque them correctly. Then check the torque periodically. I wouldn't be too concerned with whether the bolt has the head down or up.

Of course, the only way to really be sure what is best is to do a full design analysis on this, examining loads, stresses, strengths, and fatigue life. But that's not going to happen, I'm sure. Many automotive concepts are not truly "designed," they're just "built." I don't know what kind of thought or analysis went into this part, but I wouldn't be too surprised if it was minimal. The design certainly looks a little unsettling, doesn't it? I liked the post above that showed a gusset that was designed to keep the bolt out of bending. Not sure how well it worked, but in concept, it looks appealing.

One last thing: I would hesistate to call this a material failure. Though material did fail, it did so because of a high level of bending stress. That stress was most likely the result of bolt tension loss, which allowed the bolt to go into a bending mode during service. The tension loss could have been from inadequate torquing during installation, and/or it may have occurred because the design placed so much bending load on the whole system that local deformation of the system components caused pretension to be lost.

6 lines is a grade 8.

Translating from SAE to metric for tensile strength is roughly as follows:

SAE
Grade......Metric
5 .......... 8.8
8 .......... 10.5
10......... 12.9

One thing that always bothered me about the ERP kit was the bushing that adapts a SAE bolt to a metric taper. I dont like lots of adapters, bushings etc..

counterfeiting happens to metric fasteners also... I recall a recent thread where a guy bought flywheel bolts from mittlemotor, they were obvious fakes.

yes as long as the part with least section is out of a shear plane... but that really didnt matter in this instance because it is a bending failure.

check into AN bolts.. very grip specific

One thing that sticks out is that in my mind that this is the first failure of bumpp steer tie rod end Ive ever heard of.... There are thousands of cars out there with this kit on them...

Should we all be worried?

I would have to agree with all of Rob 930's posts.

I don't think there's anything wrong with the bolt, just the design. The bolt in the pictures has the grade 8 mark, the manufacturer's mark, and rolled threads. The part should not be in single shear and the threads should not be subject to bending stress, which caused the failure. At the very least I'd change the bolt every year. Next would be to get a bolt which only has enough threads to secure it. Of course the best option would be to design for double shear.

I would recommend anyone that works on track cars without an engineering degree (yes, there are some pretty lousy engineers) and/or years of experience building race cars get a copy of Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook for their's and everyone else's safety.

Air-cool-me,

The higher the bolt grade, the higher its tensile strength. Shear strength (which isn't a concern here), is generally regarded as about 50% of tensile strength. Fatigue strength (endurance limit) also increases with tensile strength; hence the wisdom that a higher grade bolt would be better in this case. One confounding factor is that the "notch sensitivity" (of higher tensile steels) tends to increase as well, which means that fatigue cracks are more prone to grow (for loads at the same percentage of the ultimate tensile strength). BTW, there was some discussion earlier about rolled or cut threads. The threads on this bolt were rolled, as are almost all bolts in this range.

I have these on my car and will look into a quality AN bolt that will fit.

Chris

You don't need the drop-link bump-steer kits unless you raise the spindles. The more you raise the spindles, the longer the drop-link you need. For slightly lower than Euro height, the rack spacers work well.

What you are shooting for is having the lower control arm and the tie-rod be parallel. If you don't raise the spindles, then adding longer drop-links will make them less and less parallel.

The rack spacers work because the Factory deliberately made them unparallel to induce toe-out during bump to make the steering more predictable. Because of this, when you lower them too far, it makes it even worse. So the little rack spacers get some of that back by reducing some of that bump toe-out, which reduces the kick-back and bump-steer to an acceptable level again.

But if you raise the spindles, you really need to drop the outer tie-rod down the same amount as you raised the spindles. Either with the drop-links, or bending the steering arms.

Chuck Said: That's an interesting fact. Making the bolt smaller probably doesn't help, particularly considering the increased load by the longer moment arm.

Ol' Carroll Smith says, on page 79 of Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook, which everyone should go out and buy, which is Copyrighted 1990 by Carroll Smith, and which quotation I am about to post is submitted for the purposes of review and "fair use," (deep breath):

Review: Smith is the man.

can someone post a pic that shows the difference between bolts in single and double shear?

thanks Rob 930, i knew there was some downside

I personally know Rob. The man is a near genius.
Thanks all,

Am I the only one that thinks this picture is bad ass?

http://forums.pelicanparts.com/uploa...1100589531.jpg

I don't know much about this subject. So fwiw

http://forums.pelicanparts.com/uploa...1100613495.jpg

http://forums.pelicanparts.com/uploa...1100613511.jpg