How a project begins can vary, mostly depending how the project comes into the body shop. The assumption is that at this point the project is already in bare metal. Sometimes all the panels are already on the car, and sometimes nothing is assembled.
Before assembling any body panels, the first step is to be sure the vehicle is set up properly. This means that to do the body work, everything should be set up exactly as the vehicle will be after it is completed. If there is a frame, the body must be mounted on the frame using the correct body mounts, and evenly torqued. Using a torque wrench can be a good way to make sure all of the mounts are the same. If the same is done at final assembly, it can help make sure the body is mounted on the frame the same way and evenly.
The vehicle needs to be on its suspension, preferably even on its wheels, or at least the wight of the vehicle on the hubs where the wheels would mount. If there are jack stands under the control arms or axles, the suspension is still loaded, but there’s a chance the vehicle’s body could flex slightly different this way. This is mostly true with roadsters and convertibles, where the body is able to flex a lot more. It’s best to just have the vehicle on the wheels, just to be sure.
The vehicle should be as level as possible. A lot of projects have square tubing in place of the coil overs while the vehicle is being built. While technically these do serve the same purpose as the actual suspension, they do not absorb any flexing if the vehicle isn’t on level ground. The best option would be coil overs in and level. If the square tubing is used, it is very important the vehicle is level, especially side to side. If it’s not, there’s a great chance the doors will not fit with the same flushness.
Once the vehicle is on its chassis and on its suspension, next on the list is all of the weather stripping and any rubber bumpers that go in the jambs. All of these have a large effect on his panels shut, and it’s very important to have them in place. Along with the rubbers being in, any door hinge bushings should be replaced if necessary. There should be nothing different used during final assembly that could cause any surprises. A lot of times, the weather strip can be taped in place during body work rather than glued. It is just important that they are there.
As for adjusting panels, it is worth spending the time to get everything adjusted as close as possible. Most often, the doors will first get adjusted to the rocker panels and the quarter panels, since they are usually fixed panels. Once the doors are close, the fenders and front end get adjusted. Of course, the biggest trick to all the panel adjustment is having patience and being willing to make sure its correct. During the assembly and adjustment step, all panels need to be assembled. If there are going to be any surprises, which there usually are, they need to be discovered during this stage. Do not assume that because the fenders and hood fit that the header panel will also fit and doesn’t need to be put on and adjusted. Assemble everything.
During all of this panel assemble and adjustment, make sure all fasteners are used, and tight. Not every door bolt needs to be tightened with each small adjustment, but before proceeding past this step, every single fastener that might effect the body needs to be in place, and needs to be tight. This includes everything, even down to something as minor as every taillight fastener, for example, should be installed
After all panels are installed and adjusted, the next step is to take the adjusting and fitment further. This is adjustments are made so that when sighting down the vehicle, everything is completely straight and flush, and no panel edges dive in.
The biggest key and tool to be used here, and throughout a lot of the body work process, is to use either aluminum flat stock or C-channel to span across panels. The point of this is to simulate where the body filler is going to be. Since this aluminum simulates body work, it shows where body filler will be. These need to be as long as possible, and spanned over as much of the body at one time as possible. How much exactly depends on the vehicle. Something like a tri-five Chevy, it would be ideal to span it from at least the center of the fender to the center of the quarter panel. By covering so much of the body, it will show how all the panels flow together. Remember, the goal is to sight down the vehicle and not see where the panels start and stop. If the flat stock was only spanned over each panel, it wouldn’t do much good for the vehicle as a whole.
Deciding what flat stock should be used, or if C-channel should be used, is based on how flexible it is. It is to be laid against the body, with the flat side against the body, so it is able to flex. The main thing is that it should not seem flimsy against the body. If it is too thin and flimsy, it will be able to follow some of the low areas, defeating the purpose of using it. If it is too rigid, it will not want to flex enough, and not represent an accurate shape of the side of the car. Some judgment is required to decide what to actually use, since every vehicle is so different, but finding the correct piece to use makes a bit difference. It should take a small amount of pressure to get the aluminum to follow the correct overall shape.
These pieces of aluminum show several things; high spots, low areas, and where panel edges are in relation to the rest of the body. The general idea is to move the high areas down, whether it’s by hammer and dolly, or by shrinking. If it’s possible to bring the low areas up, that should also be done. With the highs and lows worked out as close as possible, the attention should be turned to the panel edges.