Despite the rising popularity of the '61-66 F-Series trucks and the fact that they are beginning to get some of the recognition they strongly deserve, one of the few things not to like about them is the idea of sitting on about 18 gallons of gasoline with nothing but a seat back separating you from it. I personally consider this to be one of Ford's "not-so -better ideas."
Since I'm not one to leave well enough alone and I hate the idea of becoming a crispy critter, I began to look around for another way to store fuel in my F-100. After a little research, I ran across some info from John Niolon about putting a '65-72 Mustang tank into a '53-56 Effie. So, after some consideration, I decided that despite the difference in the frames, it should work for the '57-66 models too. John mounted his tank flange and frame on top of the bottom framerails. The later trucks have some kinks and bends in their frames, so this method would not work. I ended up mounting my tank and frame to the bottom of the framerails with the tank top sticking up between them.
As things went along, this turned out to be a fairly simple project and can be completed for $400 or less. This includes a new tank and sending unit--even if you buy everything new. It could be much cheaper, depending on how good you can scrounge.
The frame I constructed to mount the tank was built from 1x1-inch square tubing and light-weight angle parts that came from scrap from a metal building site. The extension on the filler neck came from a muffler shop. I got all that stuff for nothing. The new Mustang tank and sending unit was about $215, and the stainless steel gas fitting was another $35.
The interesting thing about the '65-72 Mustang tank is that they come in three different capacities: 16-, 20-, and 22-gallon sizes (the overall dimensions of the tank stay basically the same for all of them). The only difference in all the Mustang tanks is in the height measured from the tank flange. The 22-gallon version is 1 1/2 inches taller than the 16-gallon unit. The smaller tanks give more space between the tank and the bed frame. Each tank can be purchased new at a reasonable price, is compatible with existing fuel gauges in the trucks, and fits between the framerails with just a little bit of persuasion.
Because my tri-power 390 is thirsty, I opted for the biggest fuel load I could get. Three carburetors are harder to feed than a hungry teenage boy. Another reason I used the Mustang unit is that I didn't want to have to notch (and maybe weaken) the frame with a side fill, and since I like gadgets, I could use a stainless-steel boat-style deck fill for a fuel door that mounts directly in the floor.
One more advantage of the new Mustang tanks is that they come with a drain plug. So if you ever wanted to drop the tank, you could safely do so by draining the tank before you take it out.
In keeping with my philosophy from my "Idiots Guide to Restoration" article (Nov. '03), I broke the project up into sections. First, the tank modifications, then modifying the truck's frame, then the working on the frame to hold the tank...well, you get the picture. Finish them one step at a time and things really go smooth.
Very important note: Do not attempt to weld on a salvage yard tank that has had gas in it at any time. The vapors could cause the tank to blow-up in your face. Leave it to a professional.
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 Although it has worked for...  Although it has worked for years, the thought of sitting directly in front of the gas tank finally got to me. Removing the tank will not only give me some much-needed interior cab room, it will eliminate the gas odors from inside as well. |
 With the stock tank out of...  With the stock tank out of the way, I now have room to move the seat back some to gain some leg room or add some stereo components or storage. |
 The first problem we encountered...  The first problem we encountered was that the new Mustang tank filler neck is slanted. Because the frame is longer in the older trucks, this doesn't seem to be such a big problem. But for our later-model trucks, it is. I chose to mount the filler cap in a vertical position at the rear of the bed floor so the neck angle had to change. I had to cut the original filler neck off close to flush before I could weld a piece of muffler tubing back in a vertical orientation. |
 I used a Sawzall to cut the...  I used a Sawzall to cut the neck off. Some shop towels and magnets helped to keep metal shavings out of the tank. I cleaned up with my shop vac when
I was finished. |
 I used my free 1 1/2-inch...  I used my free 1 1/2-inch muffler tubing to put the neck back on. I cut the angle to make it fit vertical. It's kind of an eyeball thing, so don't make it more complicated than it is. The overall height can be trimmed so you can have room to put the rubber filler hose and clamps between the bed and the tank. When you weld the neck back on, don't forget to put in a vent tube. I sealed the welds with JB Weld to make sure I closed up any pinholes and to make the welds look as smooth as possible. |
 Once the tank was ready, I...  Once the tank was ready, I started on the frame. One of the problems in making the tank fit between the framerails is that the rear crossmember is in the way. This crossmember really doesn't have any other function except to stiffen the rear framerails, so I drilled out the rivets and moved it to the rear of the frame. Start with about a 1/8-inch drill as close to the center as you can get and slowly move up in drill size until the head comes off. Then use a pin punch to knock the rivet out. |
 Here's a tip to help keep...  Here's a tip to help keep some of the hot metal-shavings from landing on your belly as you drill out the rivets. I clamped the hose of my shop vac to the area and turned it on as I drilled. |
 If you flip and rotate the...  If you flip and rotate the crossmember when you move it to the back of the frame, you get some extra room for tightening clamps on the rubber hose from the tank to the fuel filler. Clamp or bolt it back in place temporarily because you'll need to trial-mount the tank and frame before you do anything else. When the project is finished and you are ready to re-install the bed, then you can weld it in solid or bolt it if you choose. |
 The second problem in making...  The second problem in making the Mustang tank fit between the framerails, is that the inside of the framerails themselves need to be trimmed. The truck's frame measured 34 inches outside to outside and 29 1/2 inches from the inside edges side to side. Since the tank body is 30 inches wide, I needed to trim the inside edge of the framerails a little so the tank would fit flush and tight on its flange and not hang down too far. I used masking tape and scribed a line 3/8-inch on the tape on both sides of the frame (3/8-inch was just right, a 1/4-inch just didn't do the job). My trusty Sawzall made short work of the trim line, and I dressed the cut with my trusty old right-angle grinder. |
 Now that the truck frame is...  Now that the truck frame is ready, it was time to construct the tank frame that will mount the tank to the truck's frame. I used lightweight 1-inch square tubing cut with the following inside dimensions: 22 1/4 x 30 3/8 inches. I used
an extra 1/4-inch to make sure the tank fits inside the frame properly. |
 I had access to a chop saw,...  I had access to a chop saw, so I mitered the ends to a 45-degree angle, but it can be done using a hacksaw or Sawzall, as shown here, if you're careful. |
 Although these 45-degree cuts...  Although these 45-degree cuts aren't required, it sure looks better and keeps water out of the inside of the frame. |
 The mounting flanges are from...  The mounting flanges are from a thin piece of 3x3 right angle I found at a metal building construction site. The front of the mount has a 2-inch kickup and bolts to the crossmember over the rear axle. |
 The rear mount was welded...  The rear mount was welded flush and bolted to the last crossmember (the one I drilled out). I drilled a 5/16-inch hole in the rear and two in the front to mount the tank's frame with 1/4-inch bolts. But I didn't mount it yet because the tank had to be installed between the top of this frame and the bottom of the truck's frame. |
 I set the tank in the mounting...  I set the tank in the mounting frame and put some sheetmetal screws through the top of the fuel tank's flange into the mounting frame to secure it. Once this was done, I temporarily clamped the fuel tank and frame in place between the framerails to make sure everything worked and fit like it was supposed to. |
 Once you have it in place...  Once you have it in place where you want it, drill up from the mounting tab through the crossmembers and temporarily attach the flanges with nuts and bolts. Put the bolts in from the top and the nuts on from the bottom. I welded the heads of the bolts to the crossmember to make tightening the nuts easier and because once the bed was on, I won't be able to reach the heads when I want to remove the tank. All that was left to do now was to re-install the bed and then locate and cut the hole for the filler neck. |