Track Pak is the 1970 heavy-duty rear-axle option for manual-transmission cars. The package brings: a 3.54:1 final drive, the 8 3/4-inch carrier with Sure-Grip limited-slip, heavy-duty cooling for the engine, and dual-circuit power-disc front brakes on most engine families. It is the basic 'serious about going fast' option.
Super Track Pak (A34) is the next step up: same idea but with the Dana 60 carrier, a 4.10 ratio, and the same cooling and brake upgrades.