Caliper Bolts and Loctite

[thkfast]

I did not replace the caliper bolts after removing my calipers for painting. When I had the car up on a hoist some time later, I had the mechanic go around and double check the tightness of the bolts, they were all good and tight. A second mechanic I spoke to also told me if he pulled the calipers off to do work, he would simply reuse the original bolts.

Has there been an example of a reused caliper bolt coming loose or failing?

[rtcat600man]

I did not replace my bolts at the time I did my brakes and rotors. I did use blue loctite. I normally replace all my bolts for any new added mods, however this time I failed......

I had a good friend of mine who is a GM mechanic helping me, (as we changed brake fluid too). We cycled the ABS system during the fluid change. So I asked him about the bolts, and his opinion was, use the loctite and you will be fine for my street application, if racing, and a peace of mind, change the bolts.

[Orange Crush 1LE]

Seriously guys, why risk re-using them? If GM's analysis and testing says they need to be replaced and the bolts yield during torquing, then stresses are through the roof and it's a legitimate safety issue. Any time you highly stress something to yield, then do it again, you are risking a catastrophic failure. I met a guy at the track that had one of his brakes come apart on the track. He veered off and totaled his car at high speed. He has neck pain to this day. You could total your life if that happens in the wrong spot.

We analyze, overload and life-test every bolted joint in the robots that I design, and most of the fasteners are yielded during installation. If they are yielded during torquing and you remove them, you need to replace them. It's your ass that's on the line. All due respect, I'm not going against what the engineers require. Spend the $30.

Another important factor- if you lubricate a bolt before installation, it reduces the friction in the threads allowing you to put excess tension in it. Loctite lubricates. So if you use Loctite, you are increasing the stresses even more on an already-yielded bolt. Bad idea.

[intensifi]

To be clear, the front Brembo caliper bolts come with red Loctite (or something similar) already on the threads. The rear Brembo caliper bolts do not come with Loctite.

Last week I bought two rear Brembo caliper bolts for something like $6.50 total. It's not a lot of money. Why risk it?

[LadyT_SS]

Originally Posted by intensifi

To be clear, the front Brembo caliper bolts come with red Loctite (or something similar) already on the threads. The rear Brembo caliper bolts do not come with Loctite.

Last week I bought two rear Brembo caliper bolts for something like $6.50 total. It's not a lot of money. Why risk it?

Blue or red loctite on the rear caliper bolts?

[rockrau]

Use the blue, red is permanent!

[sehovarter]

All - after reading the forum - I am with Orange Crush 1LE - why risk it. Torque to Yield by design is a "use once and replace" - why risk your car and your life for $40. Helping a buddy with a 2013 SS replace his rotors and pads this week and found this thread - glad I did - I just told him he owes me $45 for the bolts - but nothing for the use of my garage, tools and skills - seems like a fair deal to me - so long as he brings a 6 pack for when we are done!! Now I know that when I pull my calipers in the spring to have them powder coated Inferno Orange - I will need a new set of bolts - and now I have the part # and they reason why! Just remember - $40 for the bolts versus $40K for the car - seems like an obvious choice to me! Thanks for such a good thread!!

[Spurshot]

I wouldn't get too worked up about it. I re-used mine on the fronts when I changed rotors, mainly because I didn't realize GM recommended one-time use. I torqued them like a standard bolt. Well below the yield point. Would I do it again on purpose? If I had the new bolts in hand, probably not. If they weren't available immediately, I'd re-use them. Just don't torque them to the 30lbs + 90*.

[Deputy347k9]

Originally Posted by Spurshot

I wouldn't get too worked up about it. I re-used mine on the fronts when I changed rotors, mainly because I didn't realize GM recommended one-time use. I torqued them like a standard bolt. Well below the yield point. Would I do it again on purpose? If I had the new bolts in hand, probably not. If they weren't available immediately, I'd re-use them. Just don't torque them to the 30lbs + 90*.

Seems nearly a 50/50 split, some are very adamant in changing the "torque to yield bolts" each time removed while others would rather take the risk for $30.00.

One of the worst recommendations would be to "re-use them, just don't torque them to the 30lbs + 90 degrees! The torques specifications are there for a reason, due to heat, stress and vibration these bolts can back off or fail as if over torqued.

Early summer I was driving my 96 Impala SS onto the Marine Corps base at Cherry Point NC when I touch the brake pedal to slow down for the MP. When doing so the big beast came to an abrupt stop with a thunderous smash! What in hell was that? I initially felt the drive shaft had dropped off the front and dove into the pavement. Well that can't happen because I have a loop? MPs were as startled as if being attacked! Brake pedal felt fine, car was running like a champ, only 9,500 miles on the clock! I gently put her in reverse and released the clutch slowly, not a problem what so ever. Touch the brake and again sudden stop with a tremendous smashing noise.

I then realized the problem was directly associated with the brakes, a visually inspection front and rear saw no leaks or damage. Told the MPs I was going to roll through the gate and at a very slow speed was going to drive to the base hobby shop for further inspection.

With the wheels off I quickly found the inside of the rear right 1990 ZR1 wheel had some deep gouging? Further inspection showed the bottom caliper bolt had backed out and fell off. Each time I went to apply the brakes the caliper would swing up and jam into the wheel! $3.00 bolt you have to be kidding me! CHANGES THEM for your safety as well as others.

A friend took a picture of two front Camaro bolts, one on the left is new OEM while the one on the right is a one time used bolt with less than 4K on them. I believe the more miles on them the greater or more visible the stretch will be. If you have ever torqued one to specifications, 30 foot pounds and 90 degrees you will then realize how much stress is on them. Now add a lot of vibration?

[Spurshot]

Originally Posted by Deputy347k9

Seems nearly a 50/50 split, some are very adamant in changing the "torque to yield bolts" each time removed while others would rather take the risk for $30.00.

One of the worst recommendations would be to "re-use them, just don't torque them to the 30lbs + 90 degrees! The torques specifications are there for a reason, due to heat, stress and vibration these bolts can back off or fail as if over torqued.

Early summer I was driving my 96 Impala SS onto the Marine Corps base at Cherry Point NC when I touch the brake pedal to slow down for the MP. When doing so the big beast came to an abrupt stop with a thunderous smash! What in hell was that? I initially felt the drive shaft had dropped off the front and dove into the pavement. Well that can't happen because I have a loop? MPs were as startled as if being attacked! Brake pedal felt fine, car was running like a champ, only 9,500 miles on the clock! I gently put her in reverse and released the clutch slowly, not a problem what so ever. Touch the brake and again sudden stop with a tremendous smashing noise.

I then realized the problem was directly associated with the brakes, a visually inspection front and rear saw no leaks or damage. Told the MPs I was going to roll through the gate and at a very slow speed was going to drive to the base hobby shop for further inspection.

With the wheels off I quickly found the inside of the rear right 1990 ZR1 wheel had some deep gouging? Further inspection showed the bottom caliper bolt had backed out and fell off. Each time I went to apply the brakes the caliper would swing up and jam into the wheel! $3.00 bolt you have to be kidding me! CHANGES THEM for your safety as well as others.

A friend took a picture of two front Camaro bolts, one on the left is new OEM while the one on the right is a one time used bolt with less than 4K on them. I believe the more miles on them the greater or more visible the stretch will be. If you have ever torqued one to specifications, 30 foot pounds and 90 degrees you will then realize how much stress is on them. Now add a lot of vibration?

I do engineering for a living. If you yield a bolt twice by permanently torque stretching, as in Torque To Yield (read that as permanent deformation), it will be that much closer to full failure.

A piece of metal will only stretch so far before it fails. When a given piece of metal stretches within a certain limit, it can return to its original length. That's called "within it's elastic limit". If it stretches and doesn't return to original length, it has stretched into its "plastic region" or "beyond its elastic limit". A little more stretch and it will fail.

How much a piece of engineering steel stretches either within its elastic limit or plastic limit depends greatly on alloy and hardness. As the steel gets harder, the range of stretch in either of these regions drops down dramatically.

Your correlation of miles verses stretch of those bolts is mistaken. First these bolts are not primarily in tension in their function. They are mostly in shear. If they were to permanently stretch, due to their use/mileage, they would become loose. This is not the case. They permanently stretch (yield is the engineering term) due to the extreme torque applied to them. If you stretch them too far, they will fail. Repeated (once, twice, ?) yielding (permanent stretching) will fail the bolt. That's why they are one time use.

A TTY bolt saves going to the next size bolt that would be normal torque to stretch within elastic limits. This can save weight, cost and space.

I recommend that if you re-use these bolts, they be torqued to normal (stretch within elastic limits) torque values for that size if re-using rather than torque to yield TTY of 30lbs + 90*, which permanently stretches and puts the bolt at greater risk of failing from over stretching. The mechanism that keeps a bolt tight is the elastic stretch, which is why all bolts are torqued.

[JusticePete]

Originally Posted by Spurshot

I do engineering for a living. If you yield a bolt twice by permanently torque stretching, as in Torque To Yield (read that as permanent deformation), it will be that much closer to full failure.

A piece of metal will only stretch so far before it fails. When a given piece of metal stretches within a certain limit, it can return to its original length. That's called "within it's elastic limit". If it stretches and doesn't return to original length, it has stretched into its "plastic region" or "beyond its elastic limit". A little more stretch and it will fail.

How much a piece of engineering steel stretches either within its elastic limit or plastic limit depends greatly on alloy and hardness. As the steel gets harder, the range of stretch in either of these regions drops down dramatically.

Your correlation of miles verses stretch of those bolts is mistaken. First these bolts are not primarily in tension in their function. They are mostly in shear. If they were to permanently stretch, due to their use/mileage, they would become loose. This is not the case. They permanently stretch (yield is the engineering term) due to the extreme torque applied to them. If you stretch them too far, they will fail. Repeated (once, twice, ?) yielding (permanent stretching) will fail the bolt. That's why they are one time use.

A TTY bolt saves going to the next size bolt that would be normal torque to stretch within elastic limits. This can save weight, cost and space.

I recommend that if you re-use these bolts, they be torqued to normal (stretch within elastic limits) torque values for that size if re-using rather than torque to yield TTY of 30lbs + 90*, which permanently stretches and puts the bolt at greater risk of failing from over stretching. The mechanism that keeps a bolt tight is the elastic stretch, which is why all bolts are torqued.

You are spot on

I have been in more GM service departments than I can count doing suspension training. GM has used TTY bolts in calipers for several decades. In all my interactions I met one, ONE, GM World Class Tech that actually replaced the caliper bolts. I have lost count of the SCCA, NASA and HPDE pits and paddocks I have been in and cannot recall seeing a single racer replacing caliper bolts.

I am not advocating not replacing them. Clearly, the best practice is replacing them and we frequently do. I have had issues getting replacement nuts and bolts. When we can't get new TTY caliper or suspension bolts and nuts we reuse them with LocTite.

So the question for the metallurgy and engineering experts is -- Based on what I have seen, the vast majority of repairs made reuse TTY bolts on driveways or service departments reuse TTY bolts and nuts and it has been this way for quite some time. Why don't we see more issues and failures?

[tylerio]

Please, what is the GM part number for the caliper bolt?

[Deputy347k9]

Originally Posted by tylerio

Please, what is the GM part number for the caliper bolt?

Bolt, front caliper, quantity needed 4, part number GM 11570788

Bolt, rear caliper, quantity needed 4, part number GM 11515781

Crush gaskets/washers (if removing calipers), quantity 8, GM 21012386

[Spurshot]

Originally Posted by JusticePete

You are spot on

...

So the question for the metallurgy and engineering experts is -- Based on what I have seen, the vast majority of repairs made reuse TTY bolts on driveways or service departments reuse TTY bolts and nuts and it has been this way for quite some time. Why don't we see more issues and failures?

First, I'm not a metallurgy expert nor a structures engineer. But, I have stayed in a Holiday Inn Express and I am an engineer with test, failure, and accident experience over the decades I've worked in aerospace.

Our caliper bolts have a good portion, maybe most, of their load in shear. In other words: the caliper is trying to slide sideways (rotate with the rotor) across the bracket. This is probably the biggest reason we don't see failures of bolts in tension. There is some twisting force on the caliper, since it's hanging out off of the backside where the bracket attaches, and that causes tension force on at least one bolt.

I don't want to over complicate or over simplify, but understanding the way steel behaves as it is stressed (loaded with force, in our case tension). In the stress strain curve below for simple steels, it shows how force (stress) is applied and how the steel stretches (strain) and eventually breaks. Initially, there is a region the steel can stretch like elastic and return to original dimensions. This is called the elastic region. On that chart, it is the steep slope that is a straight line up to the yield strength. Most bolts and other objects made of steel are used within the elastic region below the yield strength. If you are ever on a steel trussed bridge and it bounces around, this is the steel flexing within the elastic region. Regular bolts are used within this region. You can tighten and loosen bolts within their elastic region a lot of times before you run into issues of fatigue. (but fatigue is another science project altogether)

On a Torque To Yield (TTY) bolt, when you torque it as the maker intended, the bolt will stretch beyond the yield strength mark on that chart. The yielding of the steel will more than likely be around the ultimate strength or left of that a bit, if torqued to maker's spec. But it will be permanently stretched. If you stretch it using the same forces (strain) again, it will push it further to the right on that curve shown, and closer to failure. That's why I would not recommend torqueing a previously torqued bolt to the same 30lbs + 90 degrees value that GM recommends for a new bolt. That goes for putting on a new bolt, torqueing to spec, then removing and reinstalling/retorqueing to spec again. I'd avoid retorqueing a bolt to the yield spec twice, regardless if you just installed it and had to remove it for some reason.

A simple test might be to measure the length of a new bolt accurately (+/- .001") , then torque per GM specs, remove it and measure the length. It should have stretched noticeably. Record that length, torque it to specs for a normal grade 5 bolt of that size, remove and measure. It should not be longer than the prior measurement. Torque it again to the TTY GM spec, remove and measure. It should be longer than the last measurement. That means it's moving along that stress strain chart curve to the right, closer toward failure, eventually.