There is considerable difference in the horizontal length of a truck spring when the truck is loaded and unloaded. When not under load, the spring is in its original curved position. When heavily loaded, the spring has a tendency to straighten out. (See Fig. 1177.)

To compensate for the difference in length when the spring is compressed, and when it is not under load, the spring seat turns on the machined end of the axle housing. To prevent any possibility of the spring seats on 4811 long rear springs rotating too far forward, a new radius rod bolt, A-21309 and AA-4773 nut have been adopted. This nut and bolt are assembled in the upper bolt hole in the radius rod with the nut on the spring seat side. In this position the nut acts as a stop in preventing the spring seat rota ting too far forward. (See Fig. 1178.)