Torque to Yield bolts on Calipers - Re-use or replace??

[Davefr]

Do you all re-use or replace TTY caliper bracket bolts? Yea I know the factory manuals say to replace them but I've heard common practice was to re-use them with Locktite blue.

Just curious.

 

[milner351]

I would not re - use any TTY bolt, period, especially not on a safety component like Brakes!

 

[PAToyota]

To expand, torque-to-yield implies that it has yielded - in other words it has stretched. Never re-use one.

 

[MoonRise]

Torque-to-Yield hardware MUST be replaced and not reused.

Anyone who says to reuse it and just stick some Locktite on it is an IDIOT.

 

[Falcon67]

X4 - TTY bolts are single use.

 

[Lotek]

X5 Torque to yield bolts are one time use only. They are designed to stretch when tightened to give more even clamping, they will only stretch so much. X1 on the idiot comment

 

[Stuart in MN]

What vehicle uses torque to yield bolts on the brake calipers brackets?

 

[Davefr]

Thanks for the replies!!

I'll replace them. They're on my G8 (fronts only).

 

[Lotek]

Thanks for the replies!!

I'll replace them. They're on my G8 (fronts only).

They should come with the pad kit.

 

[scott37300]

Are all torque to yield bolts marked in some way?

 

[MrMark]

don't all bolts stretch? After all, isn't this the whole point of generating clamping force where the bolt stretches slightly? Are torque to yield some special animal where they are just stretched "more?"

How does one know whether a bolt is torque to yield? I know head bolts but brake caliper bracket bolts? Are they marked or do you just need the factory service manual that would specify that?

 

[AdamH]

TTY bolts typically have a torque rating that you set to and then an additional turn amount to set them, i.e. 85ft/lbs + 1/4 turn.

 

[AMCguy]

For the most part yes, they do. But, a reusable bolt will return to it's original length. When a bolt yields, it no longer returns to it's original length. In this case yield means the bolt has failed or lost it's integrity. it's like pulling on a piece of taffy.

I can't answer your second question. It does open a can of worms though, doesn't it?

 

[Falcon67]

TTY bolts:
http://freeasestudyguides.com/a1_4.html
Yes, normal bolts stretch but are not taken past the yield point.

 

[Lotek]

The manual will tell you, which the tech should have for torque specs anyway, the days of winging it are over.

 

[MrMark]

For the most part yes, they do. But, a reusable bolt will return to it's original length. When a bolt yields, it no longer returns to it's original length. In this case yield means the bolt has failed or lost it's integrity. it's like pulling on a piece of taffy.

I can't answer your second question. It does open a can of worms though, doesn't it?

I see, thanks.

 

[MrMark]

The manual will tell you, the days of winging it are over.

I always buy the factory manual for any car I have. The StarMark manual is a POS compared to the GM manuals. This is one area where Merc could learn a lesson from lowly GM.

 

[MrMark]

TTY bolts:
http://freeasestudyguides.com/a1_4.html
Yes, normal bolts stretch but are not taken past the yield point.

Great! So the bolt is taken into the plastic deformation range where it is not going to return to its original length.

Question: is this a special bolt or simply an enhanced torque?


ANSWER: MOSTLY IT IS JUST A TIGHENING PROCEDURE DIFFERENCE. Same bolt.

 

[MoonRise]

don't all bolts stretch? After all, isn't this the whole point of generating clamping force where the bolt stretches slightly? Are torque to yield some special animal where they are just stretched "more?"

How does one know whether a bolt is torque to yield? I know head bolts but brake caliper bracket bolts? Are they marked or do you just need the factory service manual that would specify that?

Mark,

Sure, all bolts stretch when you tighten them.

But the difference is if you go past the "elastic limit" (where the item under consideration RETURNS to its original size once the load/force/stress is removed) and reach the "yield stress" (where the item under consideration stretches/yields PERMANENTLY and does NOT return to its original size once the load/force/stress is removed).

http://en.wikipedia.org/wiki/Yield_stress


Yes, some head bolts are of a torque-to-yield design. Even if they are not torque-to-yield, head bolts are typically so highly stressed during installation and use that they should NEVER be reused (barring some maybe special cases).

Reuse of the torque-to-yield head bolts is listed as a MAJOR cause of problems and failures with the GM Oldsmobile diesel engines, as well as a class-action lawsuit and eventual abritration settlement against GM for the same.

http://en.wikipedia.org/wiki/List_of_GM_engines

(see the section on "GM's automotive diesel history")

 

[MrMark]

A more basic question: why is moving into the plastic deformation range benefiicial in terms of generating clamping force?

ANSWER: IT should be called torque to just before yield. IT stays in the elastic range or the thing would fall apart.

 

[MoonRise]

A more basic question: why is moving into the plastic deformation range benefiicial in terms of generating clamping force?

See the Wikipedia article on Yield Stress. Note the graph of stress-vs-strain (the only graph on the page) and that the yield stress is higher than the elastic limit stress (by definition). More stress means a higher 'load/force' which means more clamping force from the bolt.

 

[MrMark]

Why not just get a stronger bolt? Why stress the bolt to yielding in the plastic deformation range? Why not just stick with a bigger or stronger bolt in the elastic deformation range to generate the required clamping force?

 

[Lotek]

Why not just get a stronger bolt? Why stress the bolt to yielding in the plastic deformation range? Why not just stick with a bigger or stronger bolt in the elastic deformation range to generate the required clamping force?

Because the clamping force can be more accurately predicted, with a torque spec, friction can cause inaccurate readings. Think of the differences between a rusty bolt, a dry bolt, and a lubed bolt, they will result in very different clamping forces for the same torque.

 

[MrMark]

Because the clamping force can be more accurately predicted, with a torque spec, friction can cause inaccurate readings. Think of the differences between a rusty bolt, a dry bolt, and a lubed bolt, they will result in very different clamping forces for the same torque.

Forgive me if I am wrong tim, but I don't think you read my post.

edit:

Ah, I had to reread that a couple of times. Yes, you did answer the question. THank you!

Excellent answer.

Now the other question was: is this a different material bolt or just a different tightening procedure?

 

[MrMark]

But Tim, I was just thinking that to get to the correct yield point you still have to rely on the initial torque setting then you add the angle, so it is still relying on torque with those failings. See what I am getting at here.

Edit: Answer is the LOW INITIAL TORQUE SETTING (before the angle turn) is more predictable

 

[MrMark]

This answers my questions

http://www.enginebuildermag.com/Article/2343/threaded_fasteners_torquetoyield_and_torquetoangle.aspx

excellent article by the way.

 

[MrMark]

Let's you get more stretch on the bolt is why it's done vs going up a size in bolt to generate the same initial clamping force. With Relaxation of gasketing you need more stretch to hold the same clamping force.

 

[AMCguy]

Another consideration given to a torque to yield bolt of a given size over a conventional bolt, might be the architecture of the component. As in an application where there is no room for a bigger just as strong, or stronger bolt. Just thinking out loud here.

 

[MrMark]

seems they could be reused (I wouldn't do it though) maybe once because they are NOT supposed to be installed past their elastic deformation range. They are to be installed just prior to their yield point for maximum elastic deformation.


Some of the comments posted in the beginning of the thread are not quite right.

 

[MrMark]

Another consideration given to a torque to yield bolt of a given size over a conventional bolt, might be the architecture of the component. As in an application where there is no room for a bigger just as strong, or stronger bolt. Just thinking out loud here.

That article explains it really well. That is why you see long thin head bolts. Max stretch.

 

[AMCguy]

This answers my questions

http://www.enginebuildermag.com/Article/2343/threaded_fasteners_torquetoyield_and_torquetoangle.aspx

excellent article by the way.

Just read this article. Now I'm smarter. Thanks for digging it up.

 

[scott37300]

So the only way to tell a TTY bolt is from a service manual? Sure would **** to be doing a simple brake job and not have a repair manual since a brake job is pretty easy when you have done a bunch. Then come across a TTY bolt on a caliper and not know it.

 

[MrMark]

They are for almost all apps the same bolt. See the article. It always pays to run through the shop manual even for "routine" work to see if any nuances are involved, like here, apparently with this G8. Although, like I said, he could probably get away with reusing these bolts if they are the original.

 

[MrMark]

Scott, I'll tell you how you'd know. To put back caliper mounting bolts or bracket mounting bolts you are going to have a torque spec. I wouldn't think about doing that job without at least researching that number. When you find that number you are going to see that it is an initial torque plus an angle and you are going to know that it is torque to yield and you should probably get new bolts. Only the half-*** would go about a safety operation like a brake job without a torque spec and wrench. So you are going to know.

 

[Hurricane_Whisperer]

don't all bolts stretch? After all, isn't this the whole point of generating clamping force where the bolt stretches slightly? Are torque to yield some special animal where they are just stretched "more?"

How does one know whether a bolt is torque to yield? I know head bolts but brake caliper bracket bolts? Are they marked or do you just need the factory service manual that would specify that?

Most bolts are in the elastic range when torqued. If you untighten them, the strain is removed and they will be the same dimensions as before tightening.

A torque to yield bolt is stretched past the point where they will snap back to the original size.

 

[MrMark]

Most bolts are in the elastic range when torqued. If you untighten them, the strain is removed and they will be the same dimensions as before tightening.

A torque to yield bolt is stretched past the point where they will snap back to the original size.

I don't think so. That wouldn't make a lot of sense from a clamping standpoint. If the bolt yields it loses clamping force.

See the linked article.

 

[MrMark]

The bolts have about 6 rundowns according to the info in the article so they obviously aren't torqued past yield. It is torque [up] to yield, not torque past yield. The reason for the few reuses must be that the material is fatigued by running near its yield point.

I'm surprised at the amount of misinformation on this subject in this thread.

 

[MrMark]

Here's a great post from another forum on this misunderstood subject

"Fastener engineering has become a science unto itself. Very few folks (even engineers) actually know how to torque a bolt correctly. Here are a few items to think about.

A torque wrench is almost useless for high performance work. The accuracy of bolt tension using a torque wrench is +-30%. The problem is not with the torque wrench but rather that any torque wrench measures frictional torque forces, not bolt tension.

The coefficient of friction of the bolt thread, nut (or threaded material), all washers and clamped material, will determine the torque value needed for a specific bolt tension. Did I mention lubrication, plating, cut or rolled threads? It should quickly become apparent that the only way to determine a torque value for a given bolt is by testing.

As was mentioned earlier, it is an easy matter to construct a bolt torque test fixture. All that is needed is a hardened steel plate of a thickness equal to the distance from the bolt head underside to the threaded surface; the effective bolt length.

In order for any bolt to perform properly, it must be stretched into its elastic range but not into its plastic range. If a bolt is overstretched into its plastic range, it will not return to its original length.

The industry standard (for all bolts regardless of strenth class) for bolt stretch is taken as 1.002 of the bolt effective length. This means that a 4 inch bolt should be torqued until the effective length becomes 4.008 inches. A 6.75 inch bolt should be stretched to 6.7635 inches.

The amount of torque that is required, using the actual bolt, washers, nut, etc., to accomplish the necessary stretch dimension now becomes the target torque value. As long as all components remain the same.

Another approach is to dismiss the use of torque entirely. If the thread pitch is known, we can calculate the angle torque necessary to accomplish the required bolt stretch.

A major pitfall, often overlooked, is the crush of the clamped material and washers. If the clamped material (or washer) is being crushed, it will be very difficult to achieve the required bolt stretch length.

A very high grade bolt can ONLY be used to clamp very rigid material with very hard washers. If a high grade bolt is threaded into low strength material or used to clamp low strength material, the bolt cannot be properly stretched without pulling the threads or crushing the clamped material. If the clamped or threaded material is has low strength, a lower grade bolt must be used. There is a reason why bolts are made to various grades; and it is not a matter of cost.

If a bolt, regardless of grade or tensile strength, is not stretched properly, it will not exert the necessary clamping force. And more importantly it will not be properly tensioned and will come loose and/or will break. LockTite, lock washers, lock nuts, safety wire, etc, are of absolutely NO value unless the bolt is properly tensioned.

If the clamping force is not substantially greater than the dynamic load forces, the bolt will stretch under load into its plastic range, change its length, lose tension and become loose. If a bolt has changed its diameter after use, it has entered its plastic range, reduced its cross sectional area and can no longer carry its design load. It must then be discarded and replaced with a bolt of proper cross sectional area.

If a fully threaded bolt is used, the threaded length will stretch under excessive load and the thread pitch will change. If a nut is run up the threads and it binds, the bolt is junk.

For longer term use in high stress enviornments, corrosion and vibration must also be carefully considered."

http://speedtalk.com/forum/viewtopic.php?p=127281&sid=294a4bd3dad45c63b38ad6f5b893e905

 

[NUTTSGT]

Hmmm, I hope none of my junk ever had TTY caliper bolts. The only one I replaced was one that fell out, after my bone head move. That could have been REAL bad, since the wife was driving it at the time.

 

[KrisKustomPaint]

Hmmm, I hope none of my junk ever had TTY caliper bolts. The only one I replaced was one that fell out, after my bone head move. That could have been REAL bad, since the wife was driving it at the time.

X2 Everything I've owned has full floating calipers and I don't see any reason a full floater would have a torque to yield bolt for the caliper pin.

What are you working on? Are you talking about the bolts that hold the caliper bracket to the spindle?

Cylinder heads use tty bolts and I've seen them reused, several times over with out a problem, but we're not talking about performance motors.