Sectioning a frame rail is merely a series of simple operations for an experienced technician; it is just another repair. However, if it is your first time to section a rail, it can create some anxiety. As with many things in life, research, advice, organization and a solid repair plan are your best foundation with this kind of work. This is not a repair in which you want to learn from your mistakes.
Repair plan
There are a few matters of concern to be mentioned before we start. One of the most critical procedures in this particular repair process is measuring. There are three things to remember when measuring: measure, measure, measure. Measuring is the compass that gives you direction during the pulling process, and it confirms when you have arrived at the correct dimensions. Measuring should be done throughout the pulling and welding process to validate that you are in tolerance. The other critical procedure is welding. If you have not been certified by some entity, whether it is I-CAR or some other professional welding program, you should consider becoming certified. Understanding what constitutes a good weld is paramount to a successful repair that guarantees the car will perform as it was engineered if it is in another collision. Before you weld the rail together, practice weld on the old cut-off sections and then destructive test them yourself. Be sure you are getting good penetration. Remember, every time someone drives this repaired vehicle, they are placing their trust in your repair.
Before the decision has been made by the technician to section the rail, a repair manual should be consulted to see the manufacturer’s recommendation. If the manufacturer recommends against sectioning, it should not be done. If the manufacturer does recommend it, take special note of the location or locations and be sure they are available to your specific repair. Guidelines for deciding to replace versus repair frame rails are generally: kink versus bend, damage in crush zones and damage in compound areas. If the damage dictates replacement of the rail, don’t be tempted or coerced into straightening the rail. This is a decision that should be made by the technician as the repair expert. Make the correct decision as a professional technician. You and the shop are liable for repairs. If you know technicians who have performed this type of repair on this particular model, ask them if they had any difficulties they can share with you.
Next, decide how much disassembly will be necessary to perform the sectioning procedure. In many cases the drivetrain may need to be removed for proper access to the rail. This is a warning: if the drivetrain needs to be removed, remove it. Don’t try to save time by working around the drivetrain if there is not enough room to perform the welding, refinishing, corrosion protection, etc.
Now that you have assembled enough information and put a plan together, let’s get that rail sectioned. There are a few different types of sectioning procedures available: open butt joint, offset butt, tapered lap joint and butt with backing or insert. Each has its preference in specific applications. We chose the tapered lap joint because we want to avoid causing the rail to have more strength than was engineered into it by the manufacturer through our repair. We will be repairing a unibody vehicle, not a body-over-frame vehicle.
Set up and measure
Disassemble the car enough to mount on a frame machine. Once the vehicle is anchored, install a measuring system to verify that the vehicle is restored to factory dimensions when you have completed the pulling. Remember to begin the pulls on the last damage to enter the unibody (last-in, first-out rule). If the damage is severe enough, a few preliminary pulls may be necessary to get 70 percent of the damage removed. This may be necessary to get computerized measuring system targets close enough to begin reading the damage. If only one rail is being replaced, you may only get the measurements close on the damaged rail until it is cut off and the new one installed.
Sectioning and welding
Once the unibody is returned to factory specifications, consult the repair manual and decide where the frame rail needs to be sectioned. It may be necessary to remove panels welded to the frame rail, such as aprons and radiator supports. Drill out the necessary spot welds and remove those panels. Now measure and scribe the exposed old frame rail on all four sides, using a small square or straightedge for accurate scribe lines. Again, be sure you have avoided crush zones, holes larger than 3mm, reinforcements inside the rail or any compound shapes. Leave 6mm of extra length on the old rail for tapering later. Now get the new frame rail.
Before cutting, verify that the new rail is the correct rail. This can be an expensive mistake if you assume it is right and cut it before you find out it was for a different model. Measure and mark the new rail, scribing it on all four sides with a straightedge or small square. If you have not performed many frame sections, this can be a good time to make a template to avoid making a measuring mistake. It may be helpful to place masking tape at the scribed lines to facilitate cutting. Draw arrows on the masking tape pointing to the side of the tape to cut on. Cutting on the wrong side of the tape can be a terrible mistake. If you forget which side of the tape to cut on and cut it on the wrong side, the rail will be too short, which ruins it.
Using a cut-off wheel, cut off a 1⁄4-in. notch on the flange of the old rail at the section to allow the rails to slide together. Notch each corner of the frame rail remaining on the vehicle with a 6mm triangle-shaped notch so that when you bend the 6mm flange down to a taper, all the notched corners close up again. Slide the new rail onto the old rail. It may be necessary to hammer-and-dolly the old rail to accept the new rail evenly. When you have the rails fitting together, you may want to remove the e-coat at the weld area to facilitate welding later. Now place the rails together and Vise Grip the two flanges together to hold the new rail in place. Once the rail is positioned, attach the measuring system again.
If using electronic measuring, place a target in the reference point on the new rail. If you are using a mechanical system, place the pointer at the desired reference point on the new rail. Make any adjustments to the position of the new rail until the measuring system confirms it is in the correct position. Get the old rail and make a few practice welds to dial in the welder correctly. When the practice welds are satisfactorily completed, place a few tack welds on the newly sectioned rail to hold it in place. Now check the measuring system and confirm the measurements have not changed. If the measurements are correct, place the other parts, such as the radiator support and apron, on the rail and measure again.
Once you have verified that the measurements are correct and the rail is in the correct position it is time to weld it solid. Take the radiator support and apron back off and weld the frame rail section up. Weld the frame rail with stitch welds of about 11⁄2 inches at a time and alternate sides in between welds to control heat. When you have the rail completely welded, check the measurements one more time.
Now it is time to dress the welds with a grinder. Install the other weld-on parts such as the radiator support and apron. If needed, punch 5⁄8-in. holes for plug welding. Punch the same number of holes in the new parts and in the same locations the plug welds are found on the old parts. Place each new part on the vehicle and position in place with the measuring system for direction. When you have them in place, weld them. If weld-through primer is recommended, use it as directed. Remember to scratch the exposed weld through primer from the center of the plug weld holes for good weld penetration. When welding is complete, clean off all weld-through primer overspray. Now check the measuring system to confirm that all parts are within the 3mm tolerance as recommended by I-CAR. If the vehicle manufacturer recommends a different acceptable tolerance, confirm the vehicle has been restored to that tolerance. When you have confirmed the correct measurements, take the measuring system off the vehicle and dress the plug welds.
Corrosion protection
Now it is time to have the refinish shop paint the necessary structural parts before reassembly. Once the structural inner parts have been painted, it is time to apply corrosion protection to the welded structural parts. To protect the welds and bare metal inside the frame rail, you should spray “an interior corrosion material” (often wax based) with a 360-degree wand. This may be one of the most important steps that is too often under-compensated for and frequently omitted. It is the most important procedure that protects the welds and structural integrity to the vehicle for years to come.
Now is the moment of truth: reassembling the vehicle to take to the refinish shop for paint. Because of the careful measuring, the outer sheet metal will bolt in place with the proper gaps. This is where the planning, research, advice, organization and repair plan will have paid off. When everything fits like it did before the wreck, the “repaired vehicle” will say, “You are a professional technician.” Good job.
