1965 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-23 -- Rear Axle

a. Rear axle ring and pinion may be any gear ratio.

b. No quick change, limited slip, or locked rears permitted.

c. Full floating rear axle compulsory, but must not alter tread width or general appearance.

d. Differential oil coolers, approved by NASCAR, permitted. Positively no electric motors allowed in trunk compartment.