Patch panels made easy: Rust busting on a '37 Chevy school bus

This 1937 Chevrolet school bus was ticketed for a complete restoration at Fast Freddie’s Rod shop in Eau Claire, Wis. Long before it would be ready for any passengers, the bus would need some extensive rust repair.

Story and photos by Brian Earnest

When Fast Freddie’s Rod Shop got a chance to renovate and customize a 1937 Chevrolet school bus, shop owner Fred Kappus Jr. knew it could be one of the more fun projects his shop had ever taken on. He also knew it could be one of the most challenging.

There aren’t a lot of how-to manuals or blueprints floating around outlining how to restore a 75-year-old bus. And this kid hauler was going to need pretty much everything: frame, drivetrain, paint, bodywork, interior — the works.

“The school bus came from the guys who have Student Transit in Eau Claire, Wis., and they run the school bus system. They’ve had the bus since the ’60s, it’s been in the family, and they are kind of looking to do a tribute to the bus,” Kappus said. “They are looking to do a modernized version and make it a lot more user friendly and a lot more drivable. It came in and had the original three-speed in it and a straight-six, so basically what we’re going to do is a chassis swap that brings a modern chassis into it. Power steering and brakes, independent suspension, big-block V-8 in it, overdrive transmission.

The tools needed for a patch panel: A Roll-Lock sanding disc, cutting tool, air duster and stone wheel.

“It will have enough power to cruise around. Do parades, whatever they want to do with it.”

To be sure, there would be a lot of tweaking, trouble-shooting and “making it up on the fly” moments for the Fast Freddie’s crew before the retro bus would be ready for the road, but one part of the process that was pretty much a straight-forward proposition was the rust-repair needs the bus had.

The good news is that most of the bad spots on the body were in flat areas, making repairs relatively easy. The bad news is that there were quite a few spots that needed attention, meaning there were going to be a number of patch panels that would need to be fabricated, welded in place and ground smooth.

The 1937 Chevy bus body actually has inner and outer sheet metal. Below the floor of the bus hangs what is really nothing more than a big apron or fender skirt that runs along the sides of the body. Both layers had rust issues. In this case, the Fast Freddie’s crew was starting with the outside sheet metal.

For a professional restoration shop, making flat patch panels without much for contours or tricky curves is pretty much “Body Restoration 101.” “On a scale of 1 to 10, this is about a 1. This is everyday work that we do,” Kappus said. “This is the starting point. This is something that pretty much anybody with a cutoff wheel, a grinder and a welder can achieve in an afternoon. This is a very basic rust repair.

A rectangular patch will be placed over this rusted area. In this case, a piece of tagboard was used as a template, which was then transferred to a piece of 18-gauge cold rolled steel. A cutting wheel is used to cut out the bad metal on the outside sheet metal of the bus. In this case, there is also an inside rocker panel, or “fender skirt” that will have to be addressed.

“We’re going to focus on a particularly rusty section of the body of the bus. We’re going to cut that bad spot out and replace it with a nice clean sheet of brand new steel. It’ll be 18-gauge cold-rolled steel.

“Basically the first step is to identify the worst of the rotted areas, cut out a rectangular piece in this particular case to make it easier to patch, then cut out a piece that fits that hole, then use some weld-through primer on the backside of the panel, the inside rocker panel, so you protect that bare metal.”

The replacement patch is first tack-welded in place, then the tacks are filled in with a finish weld all the way around the patch. The welds are then ground down with a stone wheel grinder and finished with a Roll-Lock sander — either 36- or 80-grit, or both.

The outside sheet metal is cut away and removed.

The bus also has an inside metal skirt that will be cut away with a Sawzall-type cutting tool.

Magnets are used to hold the patch panel in place while it is tack welded. The initial welds are made several inches apart by Fast Freddie’s bodyman Peter Schnoor. He then welds all the way around the panel, alternating locations so the metal doesn’t become overheated. Compressed air is used immediately after each weld to “purge” the weld and keep warping to a minimum. “You can tell when it gets just a little too hot, and when you hit it with cold air, you can actually watch it pull back out,” Schnoor noted. “On an open panel like this, you’re always going to have a little bit of warping or shrinkage, but it’s nice to try to control it as much as possible.”

The tack welds are then connected by short beads until the entire area has been filled in. Schnoor moves to a new spot after every weld so one area does not become overheated. “I skip to a different spot every time just to give it time to cool down and so I’m not throwing heat on top of heat in one area. I’ll just keep kind of following it around and filling it in as I go.”

“This is a simple repair,” Kappus said. “You do need to know how to operate a welder, of course, and do need to know how to get your heat range and wire speed set properly for the gauge of panel that you’re working on. In this case we’re going to cut out the old panel, and when we put in the new panel, we’re going to butt-weld it in so it’s a nice flat transition. After we grind it down, you won’t be able to tell we’ve repaired that area.

“The process and technique will be the same [regardless of the vehicle], it’s just the level of difficulty changes depending on if it’s a compound curve, if there are body lines involved in the rust repair. It can go way up in difficulty from here, but this is the most basic.”

Once the weld is complete, a stone wheel is used to take off the excess material and grind the patch flat. The rust is gone from this area and it’s ready for primer and bodywork. “We’ll put Duraglas over it to fill in where it’s been welded. Duraglas is a good filler and it keeps moisture out,” Schnoor said. “Then we’ll put any polyester filler that we need over that.”