Originally Posted by Revvv
It's not too hot until it boils the brake fluid, locks the calipers down, and the pads weld themselves to the rotor.
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One of the drivers for a team I consult for has had a similar experience with his personal TT3 car (370Z). He came into the last turn at NJMP Thunderbolt, the pedal sank to the floor, and he immediately pitted in. Upon stopping, he saw that he was getting drips of brake fluid dripping from the outer side of the front left caliper.
It turned out that the outer pistons had failed to retract early in the session, and the pad got hot enough that he actually put the pistons through the backing plate of the pad, and mushroomed them against the rotor.
That pad with the pair of embedded pistons now sits on his mantle as a trophy for surviving his first catastrophic brake failure. The other instructors at the PCA event he was at were duly impressed with that failure.