Patch Panels Like a Pro

The lower sides of the cowl section are probably the most common place for rust out on the Model A Ford.

You have all seen the blistering paint in this area on countless cars. On many cars the rust holes have been filled with lead, plastic body filler, covered with fiberglass, or a metal patch has been welded right on top of the rusted out area. There is a structural member just behind this area and it traps dirt and debris. This dirt which is sandwiched between these two pieces of metal absorbs moisture and the rust out occurs. The only way to eliminate this ongoing problem is cut out the effected area and weld in a patch panel. This pictorial article will take you step by step through the repair process. This can be done with the body on the car. Here we will be working with a 1930 roadster cowl.

First position the cowl patch panel on the cowl just to see how well it fits and how accurately it has been formed. There are several manufacturers of cowl patches. Some are better than others. Some have incorrect cross section at the lower bead or feature line. The only problem with this panel is the slot for the cowl band anchor is a little off. But this will be covered by the cowl band.

Actually the patch panel needs to be cut down for ease of installation . When we are done we will only have one area to fill with body filler. Photo to right shows area we will remove from cowl section. The left side cut will be down the centerline of the cowl band. The band will cover this weld and save us work. The horizontal cut must be made above the internal structural member (for ease of clamping during welding) and lower enough not to interfere with door hinge slot at right. The right side cut will be in the door pillar and hidden by the door. Mark the cowl where you plan to cut it with a soapstone or marker, as the photo at right depicts.

Mark the patch piece to match the cutout area. with tape or a marker. The tape will mark the flange offset line. The patch will actually be cut will about 1/2" above the tape. This will leave 1/2" of material for lapping. A lap joint is easier to weld than a butt joint.

Trimming and Fitting the New Patch Panels

Trimming the panel, leaving the 1/2" to create the flange. This area will be offset flanged with a flanging tool. Right photo shows the trimming of the panel end down the centerline of the cowl band slot and beads. Standard tin snips are suitable for this gauge of material.

Left photo shows the flanging pliers. Make sure the flange recesses on the back side of the patch panel. This will fit under the cowl side panel after the old material is cut out.

Checking the work that has been done. Notice the cut at the cowl band area. This weld will be hidden by the cowl band.

Removal of Damaged Area

This photo shows the method of removing the rusted out area with the use of an air powered die grinder fitted with an arbor that is holding an abrasive cut off wheel. Wheels of 3" diameter with 1/16" thickness work well with auto body sheet metal. Safety glasses are a must when doing any type of cutting or grinding operation.

Cut down the center of the cowl band area (photo left) and at the door pillar (photo right).

Removing the damaged metal skin you can see what causes the rust holes in this area. About a cup full of rust and trash fell out. It is best to cut these areas out first before you sandblast. This will allow you to do all blasting work on the cowl at one time, including the area behind the patches that are cut out. Sometimes it is necessary to repair the structural member if to much rust out is encountered.

The next article in this series will cover sandblasting, and welding the patches in place. Followed by metal prepping, body filler, sanding, and priming.

Photos and sheet metal work by Joe Gruller / Dallas Model A Ford Club