a vibration isolation suspension system comprises a support plate mounted on a main support plate on the spaced parallel frame members of a truck tractor . the support plate is mounted on a transverse pivotal axis located near the forward end of the tractor . an air bag suspension system is mounted between the support plate and the main support plate . first and second open - ended cylindrical members are attached to each of the plates and surround the air bag in sliding relationship with one another to minimize lateral shift and roll of the fifth wheel support plate . the main plate is adjustable longitudinally on the tractor frame to adjust the fifth wheel position .