I had a somewhat similar problem with my '76 Spider autocross car after installing a new brake booster. When hot, the brakes would slightly drag, the pedal was very firm, and brakes/pads/etc. would get very hot during track laps. When cold, everything was free, but a short drive on the street with light braking would cause the drag to reappear. Even though brake booster and master cylinder are supposed to be "Plug-and-play" installation with no adjustment on a hanging pedal 105 chassis, my assumption was that some tolerances stacked up and a bleed hole (or whatever) in the master cylinder was being obscured and holding pressure when the brake pedal was released. I temporally inserted .020 in. shims between the brake master cylinder and booster and the hot brake "dragging" stopped. The final solution was installing a new master cylinder and everything then worked correctly.
I posted a query about this issue a year or so back, and Jim Neil "Papajam" responded that he had heard of a rare similar condition on early transaxle chassis Alfas.
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1976 Spider (Dedicated Autocrosser, "SPICA, No Carbs")
1991 Spider Veloce (Retirement cruiser)
Scuderia Non Originale
Last edited by conedriver; 12-05-2017 at 07:16 AM.