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Old 11-26-2007, 03:53 AM
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Lower A-arm bolt for M II?

Since we have talked a lot about strut rod eliminator A-arms and how to strengthen them lately, I ask:
Where can I find a 12" long 5/8 fine threaded grade 8 or 18.8 stainless steel bolt???
That's what I need if I add the frame support bracket.
(I know 18.8 is not as strong as grade 8.)

What followed the kit was a 18.8 stainless 11" fine threaded bolt, and I must have a longer one If I add that bracket. 11 1/2" will probalby do too.
And it must be fine threaded.

I have found 18.8 stainless 5/8x12" coarse threaded, but not fine.

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Old 11-26-2007, 05:34 AM
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How about using threaded rod?
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Old 11-26-2007, 06:31 AM
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Does threade rods exsist with the specs I mentioned?
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Old 11-26-2007, 07:42 AM
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You can try McMaster-Carr to see if they have something like that..Or the local machine shop to have a rod threaded on both ends..

Sam
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Old 11-26-2007, 07:43 AM
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threaded rod is not as strong as grade 8,never use it on something as important as suspension.
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Old 11-26-2007, 07:46 AM
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Quote:
Originally Posted by 123pugsy
How about using threaded rod?
Threaded rod would be roughly the equivalent of grade 2. Your grade 8 bolt is going to have a min. tensile strength of 170,00 psi whereas the best alloy steel threaded rod you'll find is 125,000 psi.

I'd rather go with the course thread, then make sure you drill the bolt and nut so you can put a cotter pin through it. You could buy some bolts that way, although at that length you'd have the option and you'll probably have to do it yourself, which may involve breaking drill bits... If you're getting it from a bolt shop they might be able to do it for you or refer you to a machine shop that will.

The nut you can probably get, or get a castle nut, at least.
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Old 11-26-2007, 03:44 PM
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Quote:
Originally Posted by Slipangle
Threaded rod would be roughly the equivalent of grade 2. Your grade 8 bolt is going to have a min. tensile strength of 170,00 psi whereas the best alloy steel threaded rod you'll find is 125,000 psi.

I'd rather go with the course thread, then make sure you drill the bolt and nut so you can put a cotter pin through it. You could buy some bolts that way, although at that length you'd have the option and you'll probably have to do it yourself, which may involve breaking drill bits... If you're getting it from a bolt shop they might be able to do it for you or refer you to a machine shop that will.

The nut you can probably get, or get a castle nut, at least.
I think I posted too early in the morning with that one. Glad you guys piped up about it.
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Old 11-26-2007, 04:41 PM
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5/8-11 course x 11 3/4" lg. grade 5 lower control arm bolts are what came from Heidt's in my MII delux multi-fit kit. I am replacing them with 5/8-11 course x 12" lg. grade 8 (which is what Fastenal stocks) so I'll have extra length for the frame bracket. The cotter pin/castle nut idea is a good one. Price for the two bolts was $18.69, cheap insurance.
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Old 11-26-2007, 07:06 PM
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Quote:
Originally Posted by k.c.
5/8-11 course x 11 3/4" lg. grade 5 lower control arm bolts are what came from Heidt's in my MII delux multi-fit kit. I am replacing them with 5/8-11 course x 12" lg. grade 8 (which is what Fastenal stocks) so I'll have extra length for the frame bracket. The cotter pin/castle nut idea is a good one. Price for the two bolts was $18.69, cheap insurance.
Fastenal website does not list 5/8-11x 12 grade 8, did you get them local?

Update: found them

Vince

Last edited by 302 Z28; 11-26-2007 at 07:16 PM.
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Old 11-27-2007, 06:13 AM
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Yes, got em locally here in Garland. The guy said I got the last two he had on the shelf, and they had been there for a couple of years as there is just no big demand for them. But he can get more in a day or two. Glad you got yours.
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Old 11-27-2007, 06:37 AM
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I found them with the fine threads too.
Item No 18336 w/plain finish.
18982 with zink finish.

Then It's just left to find out if they sell to a suspicious, possible-communist- Norwegian....
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Old 11-27-2007, 06:47 AM
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Staleg,

Why are you so intent on fine threads? I understand that they have more thread surface area than the course which is good for tension or compression, but these bolts will be in shear. It's your business, but I'm just curious.
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Old 11-27-2007, 07:23 AM
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It's just That I want to use same threads as the A-arm bolts supported in the kit.

I've been told that fine treaded bolts are recommended in high security areas with movements, because they will stand more of that without loosing. Lock nut on coarse threads will partly prevent this but not as good as the fine threads, and supported in my Fat Man kit was both fine threads bolts AND lock nuts.

This is just what I've been told. But then again: I do this as an extra insurance, so why change to coarse threads when the fine threads probably are the most suitable alternativ?
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Old 11-27-2007, 08:05 AM
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I agree about not using threaded rod in this case for a couple of reasons but in case someone might need it some time it is available in different grades. I have several sizes in my shop now that are grade 8 equivalent that I had left over from my welding shop.
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Old 11-27-2007, 08:58 AM
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I'd like to take a moment to recommend Carroll Smith's "Nuts Bolts and Fasteners". It's really good for understanding the engineering of nuts and bolts in language that doesn't require an engineering background to understand.

I think we've established that the ideal would be a fine thread grade 8 bolt. What I'd like to add to the discussion is what that means and why it's good.

I'll be honest, off the top of my head I can't fully recall the explanation of why fine threads are better. I think the explanation has to do with each peak being like a cantilevered beam, and being that the beams are shorter on a fine thread, they deflect less. That and I think it might have to do with being smaller notches which might mean not as much of a stress concentration.

Another key characteristic of grade 8 bolts is that except for the shortest lengths, they are not fully threaded - and your 12" long bolt will not be fully threaded. A threaded rod may be equivalent to the threaded portion of a grade 8 bolt, but I doubt it is equivalent to a grade 8 bolt if you really look at the numbers. I listed numbers from what I found on McMaster-Carr. The fact is that threads are a stress riser, and having threads other than where they are needed for your nut in a shear application (more on that later) means less contact area.

Both grade 5 and grade 8 should be formed by thread rolling, which adds strength by inducing residual stresses in the surface whereas cut threads take strength away by tearing metal off. Grade 8 gets heat treatment to add strength (core hardness of Rockwell C 33-39 vs. C 25-34 for grade 5)

There are characteristics of the profile that reduce stress concentrations, but I can't recall those off the top of my head as far as which are associated with which grades, and if I site characteristics that improve strength, they might be present on aerospace or mil-spec grades but not grade 8, but examples are having shank diameters smaller than the thread major diameters (which would mean the shank doesn't contact the ID, the bolt is good for high tensile strength but a shoulder bolt would be better for shear applications) and radiussed transitions fron the shank to the head of the bolt. But when you get into aerospace grade bolts, you start talking about spending $25 and up for a 1/4"-20 bolt. You get what you pay for, tensile strength is much higher and you start getting certifications listing the parameters of the materials and processes used to create the bolt. Or am I thinking of bolts for the nuclear power industry?

Here's a decent link I found that talks about grade 5 and grade 8.
http://www.powroll.com/screwed-grade.htm

One thing I want to point out is that being a shear application, what you want is good radial contact - shear strength being equal. If you're contacting threads, you're getting closer to point contact, and you'll tend to locally yield and create notches in the inside diameter of what you're bolting, which becomes stress concentrations. Even a partially threaded bolt isn't ideal since the shank radius tends to not be a tight fit to the bore of what it's going into (and if it is, that actually takes away some tensile strength). The ideal for shear loads is the shoulder bolt because it will have the best fit to a proper hole, so you'll avoid looseness and ovalling of the hole and achieve the best contact.
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