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Originally Posted by jmatta
I wonder how many other autos this applies to? I have removed the calipers countless times on my track Porsche, only to re-use the bolts time and again.
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It's inevitable that someone will chime in with unique anecdotal information whenever an absolute is proferred. As I mentioned, untold numbers of people who are either too cheap or unknowing will reuse the bolts. That doesn't mean they were not engineered for single use.
Any threaded metal-to-metal fastener works by actually stretching and it is this stretch which actually holds the fastener in place - the tension between the threads. Simply screwing it together does not put the fastener under tension, but torqueing it does. It is this tension, not the thread-to-thread friction, which keeps the fastener in place.
Combined with the torque spec, these are not merely threaded fasteners, they are
engineered ones. They rely on the torque spec to do their jobs. Think about it - a typical caliper bolt torque spec is around 70 ft.lbs. This torque stretches the fastener and allows a bolt threaded to 70 '/" to withstand the force of a 3,000 lb. car (+momentum) being exerted on them. Well, 4 calipers/3,000lbs = 750 lbs/caliper (actually more since the front calipers do 70% of the braking). Without the tension gained from torqueing them, a 70'/" bolt simply cannot withstand this force - eventually, they will work loose. Similarly, a caliper bolt under-torqued will also eventually work loose for the same reason.
In the 30+ years I have been wrenching on cars, I have never seen a caliper bolt which wasn't recommended as a one-time bolt. That doesn't mean people aren't always aware, or heed the advice.
Threaded Mode
