1970 NASCAR International Stock Car Racing Rule Book NASCAR Grand National Championship Circuit Section 20-10 -- Brakes and Hub Assembly

a. Any interchangeable brake and drum assembly may be used. Spot or disk brakes allowed if car is produced with spot brakes as standard equipment. Dual master brake cylinders are recommended.

Wheel treads must conform to approved specifications for make and model.

b. Backing plates and drums may be drilled for better air circulation. Scoops may be used for brake cooling, but all scoops must be approved by inspector in charge [sic - .] Fans, blowers or other attachments will not be permitted. Headlight opening may be used to pick up air for brake cooling. NASCAR approved screens and ducts from the opening to the backing plates must be installed.