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Brake caliper bolt replacement


wiremanjon

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Honda requires the caliper bolts to be replaced every time you take them off. The only visual sign these bolts are different is a little dry thread locker compound on the threads. Well I’ve read the arguments and I’ve never replaced mine. I’ve had my calipers off 30 times already and yesterday I was replacing my bolts after redoing my fork seals and fresh oil. I was using a torque wrench set to 23ft/lbs. first bolt tightened and clicked. Second bolt never clicked but went until it pulled apart. I had reached the useful life cycle of the bolt apparently. I do usually apply a bit of thread lock blue to these bolts. So I’m off to the dealership in the hopes he has them in stock Tuesday. I’ll get a few extras.
Sorry to revive an old argument but it did fail and I did chafe when my friend suggested I made a rookie mistake. As far as I’m concerned, it was the fastener that failed not my mechanical abilities. Unless my torque wrench is very out of spec or threadlock radically changes the torque setting required, I’ll just replace my two right hand caliper bolts and move on!

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Kevin Cameron wrote a very informative article in Cycle World some time back about fasteners. His main point was that helical screw fasteners stretch. At some point the stretching will exceed the fatigue life of the fastener. Presumably in the case of caliper bolts, Honda want to play it very safe for reasons around litigation. It would be nice to know when each bolt is approaching it's failure point, but without microscopic inspection, that is not practical. 

 

The failure at 30 times suggests rather less operations for safety. How about 15. But I'm just guessing ( and assuming each application of force involved a calibrated torque wrench, correctly used, and an allowance made for dry or lubricated threads)..... 

 

I'm sure more thoughts will follow

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And a further thought. The theory is all great but who wants a caliper bolt shearing off at the point of them at emergency stop. Maybe we should err on the side of caution. Replacing every time seems excessive. I'm going with 10 times using a calibrated wrench and even application. What do you think?

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Using liquid threadlocker like LocTite, definitely reduces the amount of torque necessary to reach proper tightness. So if you put

LocTite on the bolts, and tighten them to the stated torque settings you are over tightening them. Anything like antiseize

will do the same thing. The liquid acts like a lubricant and requires refiguring the torque setting. I believe the setting is 23 lb.ft, and

should be reduced probably by about 20%. if using a liquid locktite. Maybe 16-18 lb.ft. This is from Loctite: "The Loctite people

recommend reducing applied torque by 20 percent from dry values when using their liquid thread-locking compounds on threaded fasteners

 

And don't forget torque settings should be reached while the torque wrench is turning. If you stop, then start turning the bolt/nut, and

the torque wrench clicks, that is not the correct torque setting. The click should occur as the wrench is turning.

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Hence we do not use torque to accurately rely to required preload. Best is to use actual elongation measurements but it is often complicated. So torque wrench it is, but is but combined with  expirience.  Use torque wrench that’s length (length, not only torque range) is correct for bolt size and mind your wrench effort while tightening.

 

I also see some rationalizing, regarding bolt replacement, why ten times  not eight? It simply doesn’t work, that’s why recommendation to replace bolt every time. For me a key is cost, and that is being held low by the Honda. Few bucks for radial caliper bolt ain’t much compared to price of pads. 

 

Lastly, how many times those calipers have to go off? Every 10k miles? 

 

 

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Cost of 4 Honda caliper bolts in UK today is £47. Methinks we are being done over.

 

I take your point though Magneto as this is a safety critical item

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I bought 4 Yamaha bolts for some R6 radial callipers. I was shocked when I heard the price, but when I picked them up and noticed how light they were it made sense. They were drilled almost to the head for weight savings. 

Another torque wrench failing is the use of extensions. It's surprising how many don't realize that they are under torquing with an extension, more so as the bolt diameter increases.

Don't believe everything you're taught. :blush:

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Actually a straight extension doesn't affect torque settings. A universal extension is a different story

if not used correctly. The main issue with extensions is that it's easy to not support the head of the

torque wrench properly, thus applying a certain amount of sideways force. Properly supported, an

extension will work just fine.

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...and I highly recommend the use of 6 point hex nuts instead of the more common 12 point hex nuts.

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6 hours ago, Presson said:

Cost of 4 Honda caliper bolts in UK today is £47. Methinks we are being done over.

 

I take your point though Magneto as this is a safety critical item

 

Gee Presson, posh people are taking you for a ride! 

Caliper bolt is number 13 on the chart below:

 

A938-A486-7926-42-F5-9862-61-E80-BAC0050

 

Radial caliper bolt cost just over 5 bucks here. That is cheap for special fastener through OEM supply chain.

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That appears to be mid-grade 5.8 or 8.8 bolt which doesn't have too much carbon.

Higher-carbon 10.9 or 12.9, which are much more fatigue-prone.

 

Hmm, I suspect broken bolt was abused somehow.

Torque of 23-lb*ft is nowhere near 10mm bolt's fatigue-limit.

If forces are kept below that fatigue level, bolt will last forever.
Can two snapped halves be re-assembled and crack meet up cleanly?

 

That torque isn't even close to yield-limit either.

If we're talking about yield-failure, that would require way more force than 23-lb*ft torque...

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4 hours ago, Magneto said:

I have to interject to this thread that fatigue in fastener does not come directly from clamping force but working force of the joint....

Unless you take it apart a bunch of times and overtorque it... 🤪

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4 hours ago, squirrelman said:

stress on those bolts is mostly in shear, and they would be quite robust, with no chance of a fracture in that mode.

 

Only fitted fastener can carry shear.  Failure mode being under torquing the joint and cycle fatigue from working force.... 

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I just use titanium fasteners, with thread lock, at a reduced installation torque (assuming I remember...).

 

Ciao,

 

JZH

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13 hours ago, Magneto said:

 

Fatigue require cyclic force. Even low cycle fatigue require 10000 cycles.... lots of brakejobs 😉

 

 

13 hours ago, Magneto said:

 

Only fitted fastener can carry shear.  Failure mode being under torquing the joint and cycle fatigue from working force.... 

 

That's what I figured, fatigue unlikely in normal usage. I suspect some sort of mistake was made that caused higher fatigue loads. Low-torque may be possibility, as that factory torque seems awfully low for such large fastener. This causes larger cycling loads from brake-usage.

 

Similar to spokes on bicycle wheels. Best to tighten them to high-tension just under limit of rims.  Too-loose spokes undergoes larger extremes between minimum to peak-loads, leaking to faster fatigue failure.

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21 hours ago, DannoXYZ said:

That appears to be mid-grade 5.8 or 8.8 bolt which doesn't have too much carbon.

Higher-carbon 10.9 or 12.9, which are much more fatigue-prone.

 

Hmm, I suspect broken bolt was abused somehow.

Torque of 23-lb*ft is nowhere near 10mm bolt's fatigue-limit.

If forces are kept below that fatigue level, bolt will last forever.
Can two snapped halves be re-assembled and crack meet up cleanly?

 

That torque isn't even close to yield-limit either.

If we're talking about yield-failure, that would require way more force than 23-lb*ft torque...

A 10 mm bolt is about the same diameter as a 3/8 bolt, and the 3/8 bolt recommended torque setting is

right around 23 lb.ft. So 23 lb.ft. for a 10 mm bolt would be about right. But a grade 8 3/8 bolt is about 44 lb.ft.

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From these:

 

https://www.boltdepot.com/fastener-information/Bolts/Metric-Recommended-Torque.aspx

https://applifast.com/wp-content/uploads/2017/07/Applifast_Conversion_Table-Torque.pdf

 

I get 40-55 lb*ft for similar strength to grade-8 bolt. Makes no sense unless Honda's using bottom-barrel bolts. 

 

Just replaced CV-axles on my Porsche last weekend. Looked up 8mm cheesehead bolt torque-specs and it was 33-36 lb*ft. Toyota and Porsche put out tech-bulletin to increase torque for head-bolts on their turbo models by +20-25% to alleviate headgasket issues.  Must be some bean-countre/engineer dictating design back in '80s.

 

Just helped friend replace rear-shock on his ST1300P,  Manual calls for replacing upper shock-mount bolt, but not bottom one. Both exact same diameter with exact same torque-spec... WTF??? Seems reversed as lower-bolt would face higher peak forces.

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Maybe the harder bolts could stand up better over time - but I wonder if the aluminum bosses on the forks could take much increased torque.  I've thought about ditching the threadlocker and drilling the bolts for safety wire, but that's not feasible on the left side caliper with the SMC on 5th and 6th gens.  Eventually when the OEM bolts go disco from mother Honda, we'll all be figuring out other bolt options for the calipers. 

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Talking about prices, I have found this website in the Netherlands cmsnl.com where the prices are good (quite low) and parts still available for older models.

Just ordered the vents for my 97 VFR from there as I could not find these in the US.

 

keyfob cmsnl.jpg

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