Jeep’s first full-time four-wheel-drive system, introduced in 1973, was Quadra-Trac.
American Motors Corporation introduced Quadra-Trac for the 1973 model-year full-size Jeep Wagoneer and Jeep Cherokee (SJ). Unlike conventional part-time systems, it allowed four-wheel drive to remain engaged on pavement, using a center differential to accommodate different front- and rear-axle speeds while turning.
The original system used a Borg-Warner transfer case and included a limited-slip center differential. Drivers could use the system in a full-time mode for normal driving or lock the differential for conditions requiring more equal torque distribution. A low-range version added extra capability for slow off-road work.
Quadra-Trac is often confused with Command-Trac, Selec-Trac, or Rock-Trac. Those names belong to later or differently configured Jeep four-wheel-drive systems. Quadra-Trac later returned in several updated forms, but its original 1973 debut was on Jeep’s full-size line.