I was looking at the Power Train Chart for the 1968 Firebird, http://firstgenfirebird.org/firebird/1968/sales_manual/O-chart1.html
and it noticed that the rear ends available for air conditioning equipped vehicles are limited. For instance for item #17 the only rear end available is the 2.53. Also you will notice that the 3.23 rear end has the exclusion (Exc. W/Air) for performance axles and has the code "N - Not Available W/Air Conditioning" in the Special Order Axles section. Does any body know the reason for this?

pontiac did not want high revs it screwed up the a/c and it ran hot.void the warrenty