Every apparatus preventive maintenance program should include a periodic check of the frame components and fasteners. Here are some things to look for the next time you get out and under your apparatus.

Fastener torque. Some fastener systems are designed to retain their torque and strength over the life of the vehicle; others require periodic retorquing. If your apparatus use common threaded bolts and nuts, you need to check the torques at least once a year, or as often as recommended by the vehicle manufacturer. The proper torques should be specified in the maintenance manual. If they aren't, use the standard torques specified for the particular grade and size of bolts. The grade can be identified by markings on the head of the bolt. Some vehicles use English bolts and nut sizes; others use metric sizes. Always use the correct torque for the bolt sizes and grades used.

Missing fasteners. All holes in the frame rails, gussets and crossmembers should have a fastener. Any empty holes, even those that serve no function, need a fastener to carry the internal stresses around the hole. The fasteners should include washers or flanged-head nuts and bolts to distribute the clamping load over a larger area and avoid stress concentrations.

Replacement fasteners. If any fastener is damaged or is extremely loose, it needs to be replaced. Do not re-use old fasteners or re-torque very loose fasteners. They have lost their strength and must be replaced with new fasteners of the proper size and grade. Do not substitute lower-grade fasteners than the ones originally installed on the vehicle — they can't provide the required strength and may contribute to frame failure.

Damaged frame components. While you are checking the frame fasteners, also check for broken or cracked frame rails, crossmembers, gussets and brackets. Damaged frame components are a serious problem, and the apparatus must be taken out of service immediately. The most common places damage occurs are the lower flanges of the frame rails, the crossmember gussets and around the rear suspension brackets. Do not attempt to weld cracks on heat-treated rails because that will only weaken the rails further. In the worst cases, the entire apparatus may have to be disassembled in order to replace the damaged components.

Corrosion. Another potential problem to look for is corrosion. Rust, or oxidation, is a common form of corrosion that attacks iron and steel components. Fortunately, rust usually can be removed and halted with a wire brush, primer and top coat of paint. A more serious problem is galvanic corrosion, which can attack any two different metals in contact with each other. On frames, the most common galvanic corrosion problem occurs when aluminum or galvanized steel brackets are mounted on steel-frame rails. In these cases, the brackets get corroded at the point of contact until they loose a great deal of material and strength. The best solution is to avoid the problem entirely by mounting steel brackets on steel rails. If corrosion already exists, the brackets may have to be replaced.

Frame Rail Drilling Guidelines

Some vehicle users unknowingly cause serious problems when they mount components on the frame rails. Drilling the wrong size holes or drilling holes in the wrong places can cause premature frame failure.

Here are some guidelines to follow when you make holes in any frame rails:

• Hole forming. Always drill and deburr holes. Never cut holes with a torch. Rough-cut holes result in stress points that can cause cracks to form.
• Hole size. Holes should not be more than 1/16 inch (0.06 inch) larger than the bolt. Holes should be round, not elongated.
• Hole location. Holes should be in the sides of the frame rails and at least 2 inches away from the upper- or lower-frame flanges and 2 inches from any other holes. Placing holes too close to the frame flanges or to other holes results in stress points that can cause cracks to form. Holes should never be drilled in the upper or lower flanges of the frame rails.