Breaker strips are needed between the upper frame rail flange and the lower body subframe to allow the frame to flex
and the body to remain rigid. The breaker strips are the width of the frame flange and extend from the rear of the body to
the front of the body subframe. Breaker strips are normally of elastomer (rubber type) material, although the older
practice of using wood breaker strips is still continuing. To provide frame flex, the front end of the breaker strips clear the
frame flanges by about 1-inch (25. 4 mm) and, by tapering down, gradually comes in contact with the frame some 18
inches (470 mm) as they run rearward. This downward tapering of the breaker strips allows the truck frame to bend and
twist during travel without the body subframe restricting and concentrating a frame cracking, high load at the front of the
body.
Shear bolts and brackets are located on each side near the rear suspension and running gear. An upper L-bracket is
bolted or welded to the body sub frame and a lower L-bracket is bolted to the heat treated frame. The two legs of these
brackets are then secured with bolts. These bolts locate the body on the frame and prevent fore-and-aft slipping and
side-to-side slipping of the body on the frame. It is true, there is no way these bolts will locate the body. They will only
hold if the twin studs or U-bolts are tight and doing their major share of body clamping. Shear bolts which have sheared
off and a shifted body indicate that the twin studs or U-bolts are loose.
Twin studs or U-bolts are spaced along the sides of the truck, clamping the body subframe onto the breaker strips and
then onto the truck frame rails. The quantity used on each side and the diameter of the rod use depends on the body and
payload being secured. The minimum diameter of each twin stud or U-bolt should not be less than 9/16-inch (14.3 mm)
for heavy truck applications. The quantity should not be less than 3 or 4 assemblies per frame rail. Two tie plates are
used on each twin stud, one on top and one on the bottom. The U-bolt uses one. To prevent deformity the tie plates
should be not less than 1/2 - inch (12.7 mm) thick metal and sized to spread the bearing load over the bottom of the frame
rail and the top of the subframe. There should be enough metal outboard of the two bolt holes edges so that at least twice
the bolt hole diameter distance is provided to any edge of the tie plate. The twin studs or U-bolts should be secured with
large, flat, hardened steel washers on the tie plates and prevailing torque type nuts on top of the washers, locking the
assembly. These nuts must be correctly torqued to the twin stud or U-bolt manufacturers recommended torque readings,
using either a known accurate torque wrench or the turn-of-the-nut method of tightening. Retorque these nuts at 100
miles, 1,000 miles, and 6 months of use after the truck has been put into service. After the first year, an annual check of
body mounting is necessary.
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