I lost two Caliper bolts both (on different sides) yesterday on my C4 to C5 upgrade kit while on the track, to prevent it from happening in the future I am going to safety wire everything. What is the best drill bit to drill the hardened caliper bolts. It there a recommended brand and compound that wont break too easy? Thanks! Other suggestions are welcome, they WERE heavily coated with high strength red locktite.

 

If it was 262 or 271 Loctite either the product was maybe "outdated" or the threads weren't clean. That I believe could be the only circumstances where "red" if it was "Loctite" branding could maybe fail. Which bolts failed? The GM or the bolts supplied with the adapter package? I'm going to guess those supplied with the kit likely. If that's the case the "fit of the thread" of the bolts is NOT a fit to the threads of the adapter. That's very likely also. Poor job on the adapters would be more likely than the quality of a mass produced bolt but then again what did they supply you with. There's much to be concerned about. The safety wire is a good idea and the drilling shouldn't be an issue.

 

Yes, new out of package locktite, and yes kit bolts failed. Any drill bit compound suggestions 12.8 strength bolts.

 

I think you would have better luck just finding the bolts from a hardware manufacturer with the heads drilled for safety wire.

I have never had that happen. Did you torque them down? And if you used thread locker that really surprises me that they could back out.

 

I did torque them, brakes got so hot melted plastic lug covers and center caps. I dont know a place local to get pre drilled bolts, they are odd sized.

 

Take your adapter brackets to a machine shop and have the threads "confirmed" and have them provide you with bolts that are a "fit". You don't need Joe hardware bolts. I believe you'll be maybe needing adapters brackets.

 

A titanium nitride coated drill bit will work.

Suggest drilling through the "corner" of adjoining flats rather than through the middle of the bolt head to opposing flats.

 

Try this place:

http://www.fastenersuperstore.com/in...FcVFMgodgx8Ajw

 

If everything got as hot as you suggest and the "fit" of the bolt to the adapters is lacking the Loctite didn't fail. I'm going to guess that you need another complete package and evaluate what you buy before you install them. You mention "odd sized" - well I'm going to speculate that the brackets were only thick enough to maybe accommodate 4 - 5 threads and they probably weren't a "good fit" either.

I don't know where your adapter package came from but I'm going to guess likely not a premium product was delivered. When I mentioned a machine shop to "confirm" - I meant check the quality of the female threaded adapters which is where the failure was.

The grade and quality of the bolt mean very little if their used in less than an ideal mating female threaded counterpart.

If everything was hot enough to melt the lug nut covers/center caps which I don't know why they would even be on at a track event then the brake hardware is likely all "suspect". I'm actually quite surprised these failures don't happen more frequently with everyone doing the brackets/adapters in their garage. I've seen a couple adapter packages that should have just been trashed and they were fresh out of the box.

 

Which bolts were they(caliper to adapter or adapter to suspension), what did you torque them to? I've got the C5 brakes and I've tracked them for over 10 years; I don't use Loctite but I check and retorque after every event. Thankfully that's never happened to me.

 

In #3 he mentioned it was the supplied hardware or "caliper to bracket" NOT the GM original hardware which holds the caliper to the knuckle originally but now the bracket to the knuckle. There's many adapter suppliers that ain't "first class"!

 

I think that's suspicious because if the hole was tapped oversize, even if you torqued it to spec, you wouldn't get the correct force on the bolt, even less as the aluminum adapter gets hot. It might even explain why Loctite was ineffective. You might want to double check the tapped holes and fasteners first.

 

I have ordered a new bolt set, it was the caliper to adapter bolts that failed, there are two larger bolts with nuts on them that didnt fail. I am still safety wiring the new bolts

 

-- trying to jog my memory here, but as I recall, there are classes of threads, or tolerance, pertaining to threaded fasteners. if a loose tolerance fit or thread class on the bolt and tapped hole was used, and even if things are torque properly, and thread locker used, it may not be sufficient for the application. for example, class 2A/1B, or 1A/1B. here's a cut and paste thing from a engineering manual on threaded fasteners -

Thread fit is a combination of allowances and tolerances and a measure of tightness or looseness
between them. A clearance fit is one that provides a free running assembly and an interference fit
is one that has a positive interference thus requiring tools for the initial run-down of the nut.
For Unified inch screw threads there are six standard classes of fit: 1B, 2B, and 3B for internal
threads; and 1A, 2A, and 3A for external threads. All are considered clearance fits. That is, they
assemble without interference. The higher the class number, the tighter the fit. The ‘A’ designates
an external thread, and ‘B’ designates an internal thread.

• Classes 1A and 1B are considered an extremely loose tolerance thread fit. This class is
suited for quick and easy assembly and disassembly. Outside of low-carbon threaded rod or
machine screws, this thread fit is rarely specified.
• Classes 2A and 2B offer optimum thread fit that balances fastener performance,
manufacturing, economy, and convenience. Nearly 90% of all commercial and industrial
fasteners use this class of thread fit.
• Classes 3A and 3B are suited for close tolerance fasteners. These fasteners are intended for
service where safety is a critical design consideration. This class of fit has restrictive
tolerances and no allowance. Socket products generally have a 3A thread fit.

I'm guessing its not a bolt failure here. unless the bolts that failed are some cheap, low tolerance, chinese junk, I'd suspect the internal threads in the bracket maybe an oversized or a loose fit.

 

No need to guess. The choice of hardware is equally as important as the quality of his product. He's not yet mentioned the source.

I mentioned "thread fit" and having a machine shop "confirm" his product yesterday first thing and since responders seem to agree so what the OP does with the product he has is entirely "his" choice. Is the new hardware and wire secured a fix? I doubt it but it seems the direction the OP is taking. He needs the hardware anyway but the without "confirmation" of the product what has he gained?

I recalled this I thought from a long while back. Hardware and product weren't likely part of a package. It could have been "incorrect" hardware also but that would have been it seems if this is correct the OP's choice of hardware.

http://forums.corvetteforum.com/1577694452-post1.html

From another forum a good "generalization" of various Loctite product usage. A Loctite product page for each would take hours. The summary is from a RC "helicopter maintenance"


271, Red: High strength threadlocker for larger diameter hardware.
262, Red: High strength threadlocker for for hardware smaller than that which uses 271 (more like heli parts). Either does a good job for our stuff, however. I see 271 most commonly in auto parts stores.
609, Green: Retaining compound, high strength, for mounting slip fit bearings to shafts. An appropriate product for tail boxes.
603, Green: Retaining compound, high strength, similar to 609 but good where the parts may be a little oily. Good for mounting oilite bushings in housings, BTW.
640: Green: Retaining compound, high strength. Similar to 609 and 603. Lacks the oil tolerance of 603. I use it where I might have trouble with adjacent bearing contamination with the product, such as start shaft bearing blocks, since it has a little greater viscosity than 603.
638, Green, rather thick: Ultra strong retaining compound for assemblies with a marked amount of slop in the fit, min 0.004". Don't try to use this stuff for our normal bearings on healthy shafts. It sets almost immediately in the tight gap, and you'll never have the chance to get the bearing into place.
290, Green: Wicking product for thread locking AFTER assembly. Medium strength, much stronger than 242 blue in my experience. Not the correct choice per loctite for bearing mounting.
242, 243 Blue: Classic medium strength threadlocker for most of our threadlocking applications. 243 is the oil tolerant version.
222MS, Purple: Low strength threadlocker for small diameter or otherwise delicate fasteners.

Bottom line:
NEVER choose a loctite product by color alone.

Loctite has way more "thread locker" and retaining products than we customarily see on the AP shelves and hardware shelves and many are used in assembly plants. I don't believe the OP's failure has anything to do with product but it was a good read and I thought worth mentioning. The "green" product has interesting properties when working with high stressed bearings/shafts etc.

 

An important note about safety wire:

This is not a solution to your problem. Safety wiring fasteners is done to retain the fastener in the unlikely but possibly disastrous event that the fastener comes loose. It is not a solution to this issue. Please be sure to address this issue in a comprehensive and proven-to-be-effective way, _then_ wire the bolts.

 

Yes you've made a good point! It's been mentioned enough I'd think that the OP this time around "confirms" the product (brackets) and the hardware before assembly. Is the product a quality production? Needs to be determined first I'd think.

 

And it's important to deal with the heat issue. If there was enough heat to melt the plastic caps over the lugnuts, I would bet the brakes are getting too hot. I would have expected some fluid boiling.

In any event, the bolts for the front caliper attaching points simply hold the guide pin to the caliper bracket. The caliper body has holes that slide over the guide pin. It could take some time for the caliper to actually fall off as the pin would have to slide complete out of the abutment bracket.

The guide pin female threads should be always completely cleaned of any old threadlocker material as should the male threads of the bolt. It doesn't hurt to simply replace the guide pins; they don't cost a lot and they are a piece common to many GM front calipers. IIRC, they are even sold as a kit containing the pin, the rubber boot and a bolt with pre-applied threadlocker.

If there is leftover threadlocker material, the old stuff would be sandwiched between the new threadlocker and may not hold.

Sounds like it's also time to add some good brake ducting

 

To answer your question about drilling. COBALT (the metal) bits will drill damn near anything. MUST be ran slow speed. So drill press or slow electric drill.

 

I have one of these jigs for drilling for safety wire. Works great..
https://www.pegasusautoracing.com/pr...asp?RecID=5738