The front twin stud or U-bolt must be positioned rearward of the front of the body approximately 18 to 24 inches (460
to 610 mm) to avoid clamping on the breaker strip taper and to allow the front end of the body subframe to spread its load
over a large section of the truck frame without a stress concentration.
J-bolts must never be used to secure a heavy truck body. The 3-bolt clamping strength is dangerously inadequate to
withstand truck operation. The J-bolt clamping force is cantilevered outboard from the frame. When the frame rails flex,
each frame rail twists, the J-bolts loosen, and the body could shift or come off of the truck.
Unless frame rail reinforcing blocks are located between the upper and lower flanges of the frame rail, the tightening
down of the twin studs or U-bolts will crush the frame initially and continue frame deformity with the truck in use. Frame
reinforcing blocks of either wood or rigid elastomer (plastic) material must be furnished at each twin stud or U-bolt
location. These blocks must be a close fit, within a 1/8 inch (3.2 mm)flange tolerance, inside of the truck frame channel,
near the web between the flanges. Since the frame twists and flexs, these blocks must be secured in their position to
prevent fore or aft shifting. The blocks should be either equipped with vertical grooves or with top and bottom keeper
straps over the inner stud or U-bolt rod. These means keep the block from working out from under the twin stud or U-bolt.
On the Military Design Tactical Trucks, a special front body mount is employed. To accommodate tactical cross-
country travel, the normal front twin stud or U-bolt has been replaced with a much more flexible method. Outboard, upper
and lower, L-brackets, secured with spring loaded bolts and nuts, provide a proportion of the clamping force necessary to
hold down the body on the frame. In addition, the springs expand and contract over rough ground much more than a solid
rod could permit. This more flexible body mount greatly prolongs the life of the truck frame in this extra severe operation
environment.
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