Rear track bar bolt axle side question - JeepForum.com
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post #1 of 15 Old 08-12-2017, 10:57 AM Thread Starter
JeffBowser
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Rear track bar bolt axle side question

Probably been asked, but search isn't my friend today. I'm looking for a source for the rear track bar bolt, axle side to get rid of the stripped torx head bolt in there now. Problem is, the only thing locally in M12 1.75 x 80 in grade 8.8 or above is all thread, I cannot find any with the stock 1/2" shoulder.

So, two questions - how important is that shoulder, and does anyone know a source for that bolt....

Thanks!

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post #2 of 15 Old 08-12-2017, 10:28 PM
Jerry Bransford
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Find a Fastenal store or their website. That's where I bought that same bolt in July when I replaced the rear track bar and bracket.

When you have a choice, buy American made.
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post #3 of 15 Old 08-13-2017, 07:36 AM Thread Starter
JeffBowser
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Originally Posted by Jerry Bransford View Post
Find a Fastenal store or their website. That's where I bought that same bolt in July when I replaced the rear track bar and bracket.
Ah, thanks. There is a store nearby, I had no idea. Thanks for the heads-up.
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post #4 of 15 Old 08-13-2017, 08:12 AM
mrblaine
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Quote:
Originally Posted by JeffBowser View Post
Probably been asked, but search isn't my friend today. I'm looking for a source for the rear track bar bolt, axle side to get rid of the stripped torx head bolt in there now. Problem is, the only thing locally in M12 1.75 x 80 in grade 8.8 or above is all thread, I cannot find any with the stock 1/2" shoulder.

So, two questions - how important is that shoulder, and does anyone know a source for that bolt....

Thanks!
The fully threaded bolt is called a tap bolt. It won't hurt a thing to run a tap bolt in that application. It also won't hurt to run one with a bit of unthreaded shank. Both work the same all other things being equal.
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post #5 of 15 Old 08-13-2017, 11:08 AM Thread Starter
JeffBowser
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Thanks for that insight, much appreciated.
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post #6 of 15 Old 08-13-2017, 03:43 PM Thread Starter
JeffBowser
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For the layman, could you explain when a shoulder is necessary, and why? Is it strength?

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Originally Posted by mrblaine View Post
The fully threaded bolt is called a tap bolt. It won't hurt a thing to run a tap bolt in that application. It also won't hurt to run one with a bit of unthreaded shank. Both work the same all other things being equal.
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post #7 of 15 Old 08-13-2017, 04:01 PM
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Originally Posted by JeffBowser View Post
For the layman, could you explain when a shoulder is necessary, and why? Is it strength?
Folks easily get confused and believe that a bolt with some amount of unthreaded shank is stronger. It isn't in 99.9% of our uses and applications because the largest diameter at the root of the thread determines the actual strength whether there is one thread or one hundred, or more. The minor diameter is still the minor diameter no matter how many of them there are or where they are.

The vast majority of our applications fall under the rules for slip critical joints which rely on tension in the bolt and the resultant clamping force developed acting on the friction between the surfaces in contact with each other to stabilize the joint. In other words, we stretch bolts to turn them into clamps. The amount of stretch we can employ is determined by bolt strength which is controlled by the bolt material, processing, and physical size.

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post #8 of 15 Old 08-14-2017, 07:59 AM Thread Starter
JeffBowser
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Thank you.

So that begs the question - if one monkeys with the bolt grade, going from grade 5 to grade 8 for example, I presume you change the clamping force for the given torque spec and a higher grade bolt will need to be torqued down more to achieve the required clamping force?
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post #9 of 15 Old 08-14-2017, 08:11 AM
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Originally Posted by JeffBowser View Post
Thank you.

So that begs the question - if one monkeys with the bolt grade, going from grade 5 to grade 8 for example, I presume you change the clamping force for the given torque spec and a higher grade bolt will need to be torqued down more to achieve the required clamping force?
Sorta, you change the torque for the higher strength alloys so you can get a higher clamping force but only sorta. If you move up to a high strength bolt like L9 or F911, they develop higher clamping force at similar torque specs because they stretch less. That doesn't hold true for the lower grades and there are other factors like thread and bolt condition, plated, dry, and lubed which you need to follow to achieve the correct amount of stretch based on just torque value.

Look up bolt torque tables and study and compare them a bit. They will show the clamping force for a given value and how they arrived at it.
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post #10 of 15 Old 08-15-2017, 07:56 AM
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Originally Posted by mrblaine View Post
Folks easily get confused and believe that a bolt with some amount of unthreaded shank is stronger. It isn't in 99.9% of our uses and applications because the largest diameter at the root of the thread determines the actual strength whether there is one thread or one hundred, or more. The minor diameter is still the minor diameter no matter how many of them there are or where they are.

The vast majority of our applications fall under the rules for slip critical joints which rely on tension in the bolt and the resultant clamping force developed acting on the friction between the surfaces in contact with each other to stabilize the joint. In other words, we stretch bolts to turn them into clamps. The amount of stretch we can employ is determined by bolt strength which is controlled by the bolt material, processing, and physical size.
My understanding was that the purpose of the shank was to 'beef up' the area directly below the fastener head which sees a stress concentration during loading and interfaces with the mounting surface. Fully threaded fasteners are great for applying clamping force because you can stretch out that entire threaded length, but they're more susceptible to failure due to shear due to the reduction in area - at least that's what I remember being taught.


Either way, I definitely agree that it shouldn't matter for 99% of our uses
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post #11 of 15 Old 08-15-2017, 11:24 AM
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Originally Posted by mmierz View Post
My understanding was that the purpose of the shank was to 'beef up' the area directly below the fastener head which sees a stress concentration during loading and interfaces with the mounting surface. Fully threaded fasteners are great for applying clamping force because you can stretch out that entire threaded length, but they're more susceptible to failure due to shear due to the reduction in area - at least that's what I remember being taught.


Either way, I definitely agree that it shouldn't matter for 99% of our uses
If you torque it to the same value, a bolt will see the same tension and provide the same clamping force whether it has an unthreaded shank or not, all other things being equal. The risk of breaking is the same.

The unthreaded shank only affects strength if you have side loading on that portion. Picture the bolt in a shackle, and imagine how much weaker it would be if you completely threaded it.

I'm sure bolts are cheaper to make if you don't thread them as much.
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post #12 of 15 Old Yesterday, 08:46 AM
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Originally Posted by JEK3 View Post
If you torque it to the same value, a bolt will see the same tension and provide the same clamping force whether it has an unthreaded shank or not, all other things being equal. The risk of breaking is the same.

The unthreaded shank only affects strength if you have side loading on that portion. Picture the bolt in a shackle, and imagine how much weaker it would be if you completely threaded it.

I'm sure bolts are cheaper to make if you don't thread them as much.
Not according to this guy. wait for it


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post #13 of 15 Old Yesterday, 09:18 AM
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Originally Posted by mrblaine View Post
Not according to this guy. wait for it
I've seen that one before (you may have been the one who linked it). Wow. So much fail - where to begin? Apparently height causes bump steer, I never knew that. We should all be lowering our Jeeps.

I'd love to see him pull his springs and cycle his suspension. If he has a paper-thickness of clearance at resting height, I'd hate to see what happens on the trail (or in the parking lot, for that matter).
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post #14 of 15 Old Today, 12:10 AM
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I used to think Jantz was smart.

He should stick to differentials.
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post #15 of 15 Old Today, 10:41 AM
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The arc of the track bar changes if you hold it level? Even with the exact same pivot point? lol
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