Identification of Material
Notice: Some frames are constructed of heat-treated steel. Do not weld or drill these frames. The use of heat in excess of 606°C (1200°F) can weaken, cause distortion, and change the characteristics of the steel.
It is critical to identify the rail material before attempting to straighten or repair a frame. The use of any method that is not recommended for the material may result in damage to the frame.
All medium duty vehicles have modified SAE 1027 heat-treated SAE J 1392-050, or SAE J 1392-080 steel rails. Measure the thickness of the frame rail in order to identify the heat-treated frame. Take the measurement at the front of the frame where there is not any reinforcement. The heat-treated rail will measure 10 mm (0.39 in) thick. There should also be an identifying label on the outside of the left rail or the reinforcement forward of the rear suspension.
Refer to Electrode Table for the use of the electrode and the chamfer according to the process for welding the SAE J 1392-050 and SAE J 1392-080 rails.
Frames
The components of a frame consist of the side rails and the crossmembers. The side rails carry the load and the crossmembers stabilize the rails. The frame assembly must be stiff enough to support the load it carries and flexible enough to absorb and distribute stress.
These vehicles have straight, full-channel, side rails. The rails should be parallel at all points along their length.
In order to prevent corrosion, it is necessary to apply a batten compound to the mating surfaces of dissimilar metals, such as an aluminum battery box that is mounted on a steel frame rail.
Attach the frame components by using grade 10.9 bolts or huck fasteners. Use prevailing torque nuts and hardened washers at each end of the bolts.
The proper frame alignment is critical to the durability and the function of many other parts of the vehicle. If the vehicle has been involved in a fire, a collision, or has been overloaded, check the frame alignment. Check the alignment if improper alignment is suspected for any other reason. Refer to Checking Frame Alignment .
