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

So i took the bolt out of the other side and again, it was about three threads holding it...Wouldn't think this would have anything to do with it shearing but way too short....Replaced them both with one's a 1/2' longer.....Also, because the bones taper in towards the back, the bolt heads wouldn't sit flush on the bones....So i took a milling bit the diameter of the head of the bolt and milled out about a 1/16th on one side of the bolt hole so now the bolt sits square on the bone....Also, when trying to put the bolt back in i had to disconnect the rear of the bones and draglink and adjust it so the axle would move back at least 3/8"s of an inch just to get everthing lined up so it also had to be bound up {pushing foward}....Took it for a quick ride and it actually felt like it steered a little better, so maybe the axle was sitting in there a kittle cockeyed

Now it's a lightweight car with the front axle at least a foot and half out in front of the crank pulley so i wouldn't think there is a lot of weight on it compared to if was sitting directly underneath the pulley but i could be wrong...

And Flathead, that last setup is the tits...Will have to look into that further

 

I don't know if I'd trust that set-up once around the block. 1/2" bolt is pretty small there...would you trust a 1/2" diameter front spindle?...they're holding up the same weight. Then there is the issue with bolting through that wishbone, if there isn't a sleve in there it's just hollow and you can't be tightening that bolt nearly enough. Another problem I can see is that as the suspension moves up and down that shackle is going to want to turn a little to adjust for the caster change...which could cause that bolt to turn itself out.

I'd redo it NOW. At the very least weld those hangers to the bones in addition to the bolt.

-Jeff

 

factory perch pin bolts are 11/16" in diameter....

that chart i posted doesn't have a listing for 11/16 tensil strength but 3/4" tensil is over double that of a 1/2"

 

RR Eddie, Loogy provided some good info. Also I believe that you have solved some of your problem with your spotface and also a longer bolt.

If you can give me a couple real good pics of the fracture surface, I can try to give a metallurgical explanation of the failure.

The biggest issue I see with your set-up is that your bolt is essentially in single shear with an added bending load. If you can provide some additional support like Flathead's, it will help tremendously.

Also, kind of related to this, but as a heads-up info for all that read this. El Gringo and myself are working on a "Metallurgy for Hot Rodders" basic tech series on several metallurgical topics. This should help everyone. Look for the first post coming soon.

 

The only thing that sucks for strength worse than fine threads is stainless hardware. I can't find the comparo chart for it, but the tensile strength is less in finethreads vs. coarse. Opposite what you'd think and I have no idea why. I read about it on some eng. site, and now I can't find it.
To give myself an out on this cause I don't know from experience I'm just spitting up some stuff I read recently when I was trying to understand the difference in fasteners. But I was surprised, I recakll they said something about risers.

 

EDDIE, What I did was machine a bung from 1" o.d. 1018 steel. It is long enough to go through the bone. It gets welded on both sides to ensure the bone is strong. It has 5/8 fine threads in it to receive a spring mount from Speedway Motors (the one you would use for spring behind axles with batwings). I use that with a jam nut. I have good thread engagement (the whole thing). I ran this set-up all summer and have about 1000 miles on it so far with no problems. And I don't drive like an old lady either. And I don't not go somewhere cause the roads are too rough. I live in central NJ, the roads suck. Looks like you could use my set-up with a little work and few $ in parts. If I had any brains I'd post pics. but I can't. It looks like your relying too much on the bolt head in your set-up. I could machine you set of bungs and mail them to you. or you could bring your bones down and I'll tig weld them in too. I'll PM you my phone #. MIKE.

 

double

 

Hate to be a nit-picker, but grade 8 has 6 marks.
5 marks is for a slightly lesser grade (don't remember if that is grade "6" or grade "7"). Grade 5 has 3 marks FWIW.


ARP might be a good choice, as well as the Caterpillar stuff, or even the aerospace/Indy stuff. But I do agree that the suspension in the picture does look scary! I recommend that you get Carroll Smith's (I think that's the author's name) book on "Nuts Bolts and Fasteners", and read it! It will talk about how you should actually use bolts in shear/etc.

 

I read somewhere that even if the bolt has the right markings, it could be a fake. If you want real grade 8 bolts, get them at the Cat dealer. They don't compromise on quality. (Bring a big fat wallet.)

pigpen

 

Just wanted to put a plug in here for Ace Hardward. They opened one here that's just around the corner and it's the best hardward store I've ever been in. It has that small town feel. As you walk in the door, someone is there to guide you to what you need. The selection of nuts and bolts is second to none. They're easy to do business with as opposed to the big box stores and I don't care if it's more money or not.

Now, I hear somewhere else that the s.s. bolts don't have the shear strengh of chassis (gr8) bolts. Does anyone know if this is true? I want to use ss bolts everywhere in the A is possible simply because I live on the coast and don't want anything that is going to corrode or rust.

This is a good thread, lot of important information here and I look forward to the metallurgy tech article that the above two guys are putting together.

As they say, details, details, details. Thanks everyone.

 

i read the fine thread vs. course thread here on the hamb too...i had planned on using fine in as many places as possible until i read that thread....made sense.....something about fine clamps tighter but is prone to stripping.....or something like that.....or you could crank harder on the coarse thread.....more ft lbs before the threads give...

 

http://www.jalopyjournal.com/forum/s...ighlight=perchAttached Thumbnails



If you gona use the bones to hold your spring this is the only way to do it and not risk yours and others lives.

 

\

The hole is going through where the front piece of the bone is slid in and welded through the main section....It's going through both

 

The fractured surface is a little mangled from me using a punch trying to spin the piece out

 

I've driven this thing for 3 years now over probably the shittiest roads in the country and this is a first....I'm really inclined to believe that that the bolt fatigued and sheared because of it binding up because of the tie rod end in the end of the bone not adjusted properly...It was pushing the axle foward at least a quarter of an inch.....The stuff i did {spotfacing the bone and the longer bolt} just made it a little more "right".....But i do like that "hoop" set-up that surrounds the bone in the pic that Flathead posted....I have a friend with a machine shop and i'm gonna give him that pic and see if he can carve me out a pair......I'm also a wrencher.....Every few months or before a trip i'll grab a fistfull of wrenches and go over all the suspension bolts.....Who knows, maybe i stretched it beyond what i should've.....

 

You are correct Stainless is pretty but crap, IMO. I mean crap by the point that the same exactly bolt non stainless will have a higher tensile strength.

Ok, I copied this from the Totally Stainless website.

"Stainless is a series of alloy steels which contain at least 12% chromium. Such steels will not rust when exposed to weather. The most common stainless steel is 304 which is an 18-8 alloy containing at least 18% chromium and 8% nickel. 304 is a non magnetic steel. The metric designation for 304 is A-2. Even more corrosion resistant alloys, such as 316, are available for some of our product line and are a good choice for high corrosion environments such as marine use. We carry medium strength hex and socket head cap screws made from strain hardened 316 in metric sizes. These fasteners have a strength designation of 80 and are approximately equivalent to metric 8.8 or a US grade 5. We have an extensive line of high strength stainless as strong or stronger than US grade 8. The high strength bolts are made from age or precipitation hardened stainless and have a polished finish.

Stainless steel is superior to chrome plating because it won't crack or peel as it isn't a surface coating but the substance from which the fastener is made. Because stainless steel is softer than medium carbon steels (it only seems harder because it work-hardens) it tends to gall. Always use anti-Seize or a similar product on the threads."

I think this is marketing BS, because I don't understand how Stainless steel can be stronger than a grade 8? How is that possible? I've never seen it over 45 rockwell C.

 

It all depends on the type of stainless steels used. In general 300 series stainless will be lower strength, but these alloys can be cold worked to extremely high strength. Precipitation hardened grades of stainless can have even higher strengths. My company makes a precipitation hardened (PH grade) stainless steel that has a tensile strength of nearly 300,000 psi, which is twice that of Grade 8. All in all, the metallurgy of Grade 8 bolts is far from "state of the art".

I'll add this to the topics that Terry and I will address in our metallurgy series.

 

I like that design with a bracket encircling the bone, but it looks 'added on' to my eyes.
Henrys perch pins are forged and plently beefy, so i used those. I had bungs made up with a taper inside to match the perch pin, then welded them into the bones, across the joint between the forged end piece and the welded tubular part.I also used castleated nuts to make it look original. Putting the spring mounts further back up the bones is horrible and screams 'ratrod 2003' to me. I wanted mine to look like a spring configuration that could have been a factory setup in a slightly altered parallel world where cars were set to ride low from the factory (oh how i want to live in that world!)

 

Doesn't matter --- Each size fastener has an assigned torque value , tighten it to that & you need no more torque & I assure you the assigned value is short of the stripping point. Overtorquing leads to stretching & eventual failure .
Now with that covered the next thing is to insure you are using a proper size fastener for the load incurred, if the load exceeds the design size ---- failure . Also improperly torqued, ( too little) will allow movement of the parts secured when load is applied , repeated cyles of load -unload , if the clamping force of the secured joint is not equal to or more than the load WILL result in fAILURE --- IT IS ONLY A QUESTION OF HOW LONG IT WILL TAKE .

 

Ideally, since the bones move in an arc, the perch bolt (if it is going into the bone) needs to be able to pivot, since the spring eye can't turn in the same arc. Somethings' got to give!

 

Maybe thr 1/2" bolt is not big enough.I made the perch's for my roadster with3/4" bolt's.3/4 might be overkill but i'd rather have one to big than not big enough.Gregg

 

300,000 PSI DANG!!!!
How does it hold up in shear?

I've been reading your metallurgy thread. Sorry couldn't get through it in one read had to take a brake from serious study and thought.
I'm a total novice to this but am trying to learn all the difference, and the properties of eahc quality. What I have a hard time with is all the "DIFFERENT" ways or rating, and I guess you could call it different "STANDARDS"
Anyway, I'll get my hands around it soon enough. Thanks for the help.

 

I had renowned hot rod fabricator, drag racer and fellow HAMB member Bob Hindman make up a set of perches for my Model T sedan project. They use 5/8" grade 8 bolts and run through sleeves in the wishbone. I put a lot of effort into ensuring the perches, shackles, and spring were in perfect alignment and free to rotate on axis.

Bob does not charge much for them. Sometimes you need some help from a pro.

 

Bob appears to do them right.
The way the failed ones are made, any looseness in the assembly will allow bending forces to overstress the threaded part of the bolt.
A 1/2" bolt is only 1/2" in the shouldered area...not thru the threads.
If maximum available strength is the requirement...then the failed one is fabbed backwards...causing the bolt thread itself to become a stressriser.

 

I have not read the thread that you guys are refering to comparing fine versus coarse threaded bolts but what you are saying goes against everything that I have learned and was taught about bolts.

The minor diameter (the smallest diameter of the screw thread) of a coarse threaded bolt is smaller than the minor diameter of a fine threaded bolt. Think of it this way, if you were to chuck a coarse thread bolt and a fine thread bolt into a lathe and turn the threads off right down to the base of the thread, the diameter of the remaining material will be greater on the fine threaded bolt than on the coarse threaded bolt. So in essence, the coarse threaded bolt will be weaker than a fine threaded bolt with everything else being equal.

There's a reason that the aerospace industry uses fine threads alsmost exclusively.

Given the choice, fine threads should be used for all applications except where a bolt or stud needs to be threaded into castings such as transmissions or engine blocks.

 

No, but I could use a friend there! We've bought a fair amount of hardware from Coast, as most of the race cars i work on use AN bolts exclusively.

BTW, it's a good idea to read up on airframe bolts, as they are very handy for suspension systems. With "gas station" hardware, you ALWAYS have too much thread and not enough shank (I believe part of the original problem on this thread). AN bolts are expensive, but if you buy only what you need in the planning stages of a build, they are the best solution IMHO.

 

I'm suprised that no one has mentioned Carroll Smith's book "Engineer to Win". In it, Smith provides excellent information on metallurgy and threaded fasteners that has guided racers for decades. My copy was published in 1984 by Motorbooks International. Carroll Smith writes this stuff so that us regular guys can understand it. Although it is oriented towards sporty car construction, it has lots of valuable information applicable to hot rod construction.

 

BibOveralls, I hate to rain on your parade some, but the welding doen on that bolt to the sleeve has reduced your bolt down to less than grade 8. Or whatever it started as. The welding causes the heat treatment in the bolt to be messed up, it loses strength, because you are essentially tempering the bolt more.

Wait for the metallurgy tech series on heat treating and this will mnake mroe sense.

I am not saying that your parts won't work. Just that I have some concerns. In addition to your welding heat affects, I also see by your design that ALL of the load and stress is going through that weld on the sleeve. Hope you have good confidence in that weld, as it is holding everything up. Once again, I am simply making observations based on a small amount of pictures and data in your post.

 

lmao

 

Jeezus H., I wouldn't drive those 2 feet.

Those are mock up, push around the shop only.