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Discussion Starter #1 (Edited)
Like some of you out there, I have asked for information about the bolts that are "required" when doing suspension work. I could never get anyone to measure their old bolt. Well, I am getting close to installing my suspension pieces so I just bit the bullet and purchased them from GM. They showed up and I have measured them. From head to end, here are the specs (measured with a pair of digital readout calipers):

PN: 92038482
Position: GTO Rear Crossmember (Cradle) Bushing
Head Marking: M8.8 with an embossed hexagon with what looks like a Pontiac arrowhead in the hexagon
Hex Head: 18mm
Washer Head Diameter: 1.1"
Smooth Shank Under Head: 0.549" diameter x 0.285" long
Smooth Shank Taper Length: 0.085"
Smooth Shank After Taper: 0.548" diameter x 0.885" long
Threaded Shank: 0.548 diameter x 3.091" long
Thread spec: M14 x 1.5)
Smooth Shank After Thread: 0.462" diameter x 0.204" long
(The length on this one is variable because it is not cleanly
Taper to point: Not easily measurable diameter or length.
Overall Length: 5.319"
Applied threadlocker: Blue, starting ~0.75" from pointed end to ~1.5" from same end
Torque spec: 90 ft-lbs + 40 degrees

All of the lengths except the overall length were actually measured from the washer head to the feature and then subtracted from the previous).

The fact that it's Class 8.8 (metric equivalent to Grade 5) surprises me. Every other suspension bolt I've had the ability to examine has been Class 10.9 (metric equivalent to Grade 8). I thought that that might be the reason it yields.

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If I had merely wanted to measure them, I could have purchased just 1 bolt. I had a test in mind, though. I wanted to see if they actually yielded. So, I bought 2 bolts in the event that they did and I would have to put a new one in after the 2nd measuring session.

So, tonight was the night for the test.

Step 1: I used a breaker bar with a pipe extension to get the old bolt out (and it was a cast iron b!tch, too).

Step 2: I installed the exact bolt that I measured and torqued it to 92 ft-lbs with a torque wrench.

Sep 3: I turned the bolt another 40* (closer to 45*, really) with the breaker bar (cheater bar not required).

Step 4: I took the bolt out and re-measured it. It came out a LOT easier this time due to the threadlocker/corrosion not setting up.

Result: Zero change in overall length, diameters, or intermediary feature distances. That is they do not yield.

My conclusion: The FSM says Remove & Discard due to the threadlocker. I will have zero concerns about re-using this bolt after cleaning the threads and applying new threadlocker (which is what I did after re-measuring).

Maybe we should call them RAD (remove and discard) bolts from now on.

Stay tuned for a repeat of this test with the rear diff bolts and the front and rear front cradle bolts.
 

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GTO
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Good info, keep up the testing. I have always had a hard time with replacing these TTY bolts that look so stout.

Can you tell if the threads are affected?? That may be what yields.
 

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Discussion Starter #3
Other than the remnants of threadlocker, the threads on the original bolt look perfect. They're uniformly spaced for the whole threaded length and still have the dichromate gold finish. The thread diameter measures the same for the whole length of thread, too.

It would be crazy to weld an interference-fit nut onto as major a structure as a vehicle body.
 

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I know from my experiences when I owned a VW most of the TTY bolts only needed threadlock re-applied. They were all reusable but the service manuals stated to replace them. The dealer techs told me that they did not need to be replaced and that they themselves re-used the bolts and just added new threadlock.
This is probably the same case w/ the GTO.
 

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Ssshhh, I reused the cradle bolts with new Loctite. No f'n way do those bolts yield unless you use a CMM to measure 'em afterward (I have a Zeiss Spectrum but didn't think to test). Also, you will need the mother of all cheater bars to tighten them, I don't think they make torque wrenches that go high enough. You literally can't tighten these bolts enough, and if there are the slightest bit loose, you will have a clunk.
 

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I think I know why the bolts are still the same length. I play with a lot of metals.

It's Young's Modulus of Elasticity. Bolts stretch and extend only when they are installed. They will return to their original length when removed, unless they were overtightened or damaged by heat.

TTY bolts are designed for a specific application and installed in a way to have a very wide range of elasticity. In other words, they have a wide working range before they are permanently deformed. Think of a bolt (a TTY in particular) as a cable on a bridge.

When a bridge cable has tension on it, it's working and will handle plenty of weight. Some bridges sag about 12 inches when loaded with trains, trucks and GTOs. These cables will hold all the weight and when the bridge is empty, it will go back to its original height. That means the cables have a working range of 12 inches. Anything past that, (by too much weight or heat) and the cables will go into permanent deformation and shortly thereafter, snap. Just like any bolt you've tried to overtighten over the years.

If you were able to measure an increase in length after you removed a bolt, that bolt is no good as its about to snap. It is in its range of plasticity and after plasticity, there's the burst point.

It is recommended that TTY bolts are to be replaced anytime they come back out. That is because they have been "unsettled" from their happy little homes where they were perfectly installed with all-new threads and components. Personally, I've re-used TTY bolts with great success. Although it's not recommended, with proper cleaning and thread chasing, any bolt can be reused if it hasn't entered its range of plasticity.

Hope that helps. I probably confused a lot of people.
 

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Kollar Racing Products
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If great information about bolts, nuts etc is needed ...ARP...the manufacturer of the best rod bolts and head bolts on the planet has volumes of easy to understand information on their website. I cant find the specific page that applies to TTY headbolts but I know its in there somewhere.
 

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Still Hangin'...
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If great information about bolts, nuts etc is needed ...ARP...the manufacturer of the best rod bolts and head bolts on the planet has volumes of easy to understand information on their website. I cant find the specific page that applies to TTY headbolts but I know its in there somewhere.
Oh yes, I got it from an old printed piece ARP gave out years ago. Still keep it close to my desk.
 

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Thanks for bringing this information to light, 24GTOUinFL. I am very sure that other bolts that are known as TTY are also not TTY. Strut ear mount bolts were called to be TTY for my Mustang, but reusing them posed no problems for me in the period of 7 years of taking struts on and off. I highly suspect GM is no different in this aspect.
 

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Still a communist state
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I reused mine,didnt see a problem with it at all
 

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Because race car
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I think I know why the bolts are still the same length. I play with a lot of metals.

It's Young's Modulus of Elasticity. Bolts stretch and extend only when they are installed. They will return to their original length when removed, unless they were overtightened or damaged by heat.

TTY bolts are designed for a specific application and installed in a way to have a very wide range of elasticity. In other words, they have a wide working range before they are permanently deformed. Think of a bolt (a TTY in particular) as a cable on a bridge.

When a bridge cable has tension on it, it's working and will handle plenty of weight. Some bridges sag about 12 inches when loaded with trains, trucks and GTOs. These cables will hold all the weight and when the bridge is empty, it will go back to its original height. That means the cables have a working range of 12 inches. Anything past that, (by too much weight or heat) and the cables will go into permanent deformation and shortly thereafter, snap. Just like any bolt you've tried to overtighten over the years.

If you were able to measure an increase in length after you removed a bolt, that bolt is no good as its about to snap. It is in its range of plasticity and after plasticity, there's the burst point.

It is recommended that TTY bolts are to be replaced anytime they come back out. That is because they have been "unsettled" from their happy little homes where they were perfectly installed with all-new threads and components. Personally, I've re-used TTY bolts with great success. Although it's not recommended, with proper cleaning and thread chasing, any bolt can be reused if it hasn't entered its range of plasticity.

Hope that helps. I probably confused a lot of people.
I think you are missing the point.

Torque to Yield means that it YIELDS! Any metal will elastically deform within a certain load/stress/deflection range. Elastic deformation means that the part will always come back to it's original shape. As soon as you exceed this elastic limit, the part will plastically (pernanently) deform. This does not necessarily mean the part is about to break....but you are definitely putting a lot of load onto this part.

If you measure a "torque to yield" bolt before and after and it hasn't changed shape...than it hasn't yielded!
 

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Still Hangin'...
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Er, it was meant to clarify why his bolts were still the same length. It won't yield if it never leaves its elasticity range sitting in your hand. As an authority on metallurgy, surely you know that.
 

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I had to drop my diff a little to fix a small leak that developed when I changed the oil (factory must have tightened the drain plug before sealant cured, so it 'pulled' when removed. It was tight as hell). Had to remove 4 bolts holding the pumpkin cover to the 'chassis'. When looking for the torque realized they were TTY. However, didn't take much effort to remove those, and the bolts look pretty stout to easily hold that torque without 'yielding'. So I reused them, but without the additional 'degrees' of rotation. Didn't see the need, just like I don't follow torque recommendations for drain plugs. No problems.

Bottom line is if the bolts are TTY, they are, but unless they reach their threshold, they're just like any other bolt. It's hard to know if they reached that point without speciallized equipment, but in some cases, like those diff bolts, I don't think it was even close. Besides, the plate where those 4 bolts mount seems flimsy as hell, with only a handful of 'tack welds' holding it to a cross member, so the weakest link is by far that part, not the bolts, but that's just my opinon. A more critical looking bolt that is TTY, I'd replace it for sure.
I personally think 90% of the reason to call for new bolts is to make a profit, rather than real need, but could be wrong. It's beyond me why even use 'disposable' bolts on a car; unbelievable. Only GM. Later gang.
JC
 

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I had to drop my diff a little to fix a small leak that developed when I changed the oil (factory must have tightened the drain plug before sealant cured, so it 'pulled' when removed. It was tight as hell). Had to remove 4 bolts holding the pumpkin cover to the 'chassis'. When looking for the torque realized they were TTY. However, didn't take much effort to remove those, and the bolts look pretty stout to easily hold that torque without 'yielding'. So I reused them, but without the additional 'degrees' of rotation. Didn't see the need, just like I don't follow torque recommendations for drain plugs. No problems.

Bottom line is if the bolts are TTY, they are, but unless they reach their threshold, they're just like any other bolt. It's hard to know if they reached that point without speciallized equipment, but in some cases, like those diff bolts, I don't think it was even close. Besides, the plate where those 4 bolts mount seems flimsy as hell, with only a handful of 'tack welds' holding it to a cross member, so the weakest link is by far that part, not the bolts, but that's just my opinon. A more critical looking bolt that is TTY, I'd replace it for sure.
I personally think 90% of the reason to call for new bolts is to make a profit, rather than real need, but could be wrong. It's beyond me why even use 'disposable' bolts on a car; unbelievable. Only GM. Later gang.
JC
Good points here. TTY bolts are very commonplace in today's manufacturing world. Beyond the engine, these are everywhere. Truth be told, they should be replaced but I've even reused head bolts in a 550 rwhp LS1 with nitrous.
 

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May I quote you on that?
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In another thread, someone proposed a concept that makes a lot of sense. GM recommends replacing the bolts because it is cheaper than paying a tech to piss around with removing the old Loctite.
 

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STANd YOUR GROUND.
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In another thread, someone proposed a concept that makes a lot of sense. GM recommends replacing the bolts because it is cheaper than paying a tech to piss around with removing the old Loctite.
ding ding ding, winner
 

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Another possibility here is that the torque spec + degrees ends up with a preload condition that is very close to yield. Ideally, you want your bolts to be as close to yield with preload as you can get. GM probably just specs a certain torque + degree rotation which gives them 85% to 110% yield or so, depending on how the bolt comes in. So if you pull 100 bolts, maybe only 5 of them will have actually been torqued to yield, so they just tell everybody to replace them just to be safe.

But the theory of not paying a tech to clean up the old bolt is quite likely, also.
 

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So it goes.
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Yes they do

I have seen those TTY bolts after 25,000+ miles with my own eyes.

They do not change dimensions; its the threads that stretch/yield.

I had my crossmember bushings replaced at my local Pedders shop and the installer Tommy brought out the TTY bolts for us to look at.

You can see on the threads near the end of the bolt, where they grab the frame of the car, are stretched. Instead of being straight and uniform, the threads near the top are pulled upwards. Imagine a heavy weight pulling down on the bolt while its bolted up into the frame, and you'll see what I'm getting at.

It was obvious to the naked eye that those bolts had warped.
 

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Discussion Starter #20
Beach Goat: How far from the end of the bolt were these stretched threads?
 
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