Gas Tank Upgrade

As many of you are aware, gas tanks for the early (71-73) Mavericks and Comets are not reproduced. The later tanks are available but they have clearance problems with the rear valance panel. Another problem with the design is the way it was offset to the left to provide clearance for the muffler. This gives very little room on the left side to run an exhaust pipe for duals. The solution I found was to install an early Mustang tank. The benefits are that they are easily available. You can get a kit that includes a new tank with a drain, new sending unit, hose, and clamps for less than $150. The kits without drains are under $130. The great thing is you will have room on both sides of the tank to run 4” pipes with room to spare. I did all my modifications with normal hand tools, air powered cut off wheel, and a mig welder. A set of torches will help in reforming the tank straps but are not necessary. I bought my tank kit from CJ Poney Parts. 1-800-888-6473. You will also need some scrap 16ga steel to make some brackets and the following 2 parts from Ford. Grommet-F6TZ9B076AA, Vent Valve-E7DZ9B593A.

Here is the finished product. With the tank more centered, and the fuel pick up moved to the front, you can see, there is plenty of room on the left side to run any size pipe you would like.

Lets get started

First thing is to acquire all your parts and remove your old tank. You also need to remove the brackets that are welded to the trunk floor that are there to keep the tank from sliding around. The left tank strap mounts can be used as is. The right strap mounts need to be moved over approximately 4 ¼ inches. The straps also need to be shortened. Use my measurements as a guide only. Every situation is a little different so double check your own measurements before cutting or welding anything.

Mark the new cut out and leave at least ¼” to the outside edge. You will also need to drill a couple of small holes to weld your reinforcement plate you will be making and sliding inside this piece. Just look and see how the original is done and duplicate it. I made my plate a little long and used that existing hole on the bottom to tack my plate in as well as drilling another hole in the face.

This is the reinforcement plate I made. It slides into the channel and is held in place by the 2 plug welds. Make this from at least 16ga metal.

The rear crossmember has a kickup and will need to be flattened where the new mount will be. Lay out the new mount. You can use the existing access hole for the head of the bolt as shown. Go about ¾” past the end of the new slot and cut the edges starting at the bend as shown. Once the plate is free, tap the plate flat.

This is the reinforcement plate. It sits on top of the plate you just cut free on the rear crossmember. The back lip needs to be flush with the edge of the crossmember. The hole is to plug weld the 2 plates together. Weld this all the way around the outside edges but not in the slot.

Set the plate you made on the crossmember. Everything should be flat. This will box in the mount. There will be gaps on the sides but you can fill them in with the welder. The completed rear mount should look like this. That pretty much takes care of the hard stuff

Next thing to do is roll the rear edge of the new tank. It sits too far forward as is so we need to roll the edge to move it back. I used a rubber mallet and slowly worked from one edge across to the other making a little more bend with each pass. You need it to be 90 degrees to the top when finished. You also need to bend it down, not up. Once this is done you can test fit the tank. The filler neck in the tank should be centered in the opening in the trunk floor.

Now we need to shorten the straps. I found the straps needed to be shortened the same length of the reinforcement plate on the bolt end. I used a torched to heat it up cherry red, flatten the end, and then bend it back over on itself, right at the edge of the doubled plate. I used the original hole to plug weld it to itself. Then all you have to do is drill a new hole and duplicate the original “L” shaped bend.

The next thing you need to make is some brackets. The straps will hold the tank up but a tank of gas can weigh over 100 lbs. Hard breaking or cornering can cause the tank to shift around. We need to weld some stops to prevent this. Make 4 of these brackets. I made mine ¾” tall and 1 ½” across the bottom. Once again, use at least 16ga steel.

After you have all the mounts done, straps shortened, and brackets made, mount the tank in the car. Make sure it is as far back as it can go. The filler neck should be in the center of the opening in the trunk floor. Once the tank is mounted, take your filler neck and start cutting the bottom off a little at a time until it slides in the back panel and is no more than ¼” above the filler tube on the tank. Both tubes should line up. Make any adjustments needed and trim the connecting hose so that you have just enough overlap to put a clamp on each tube. You want to keep this connection as low as possible so that the floor seal will cover it all up when completed.

Now we need to weld the 4 brackets on. I put 2 of them in the front and one on each side. Slide them until they touch the flange of the tank and tack them in place. Then remove the tank and finish welding them.

The Next step is to install the vent fitting in the top of the tank. Mustangs use a vented cap where as Mavericks and Comets do not. We run our gas fumes out the top vent, route it into a carbon canister under the hood, and send it into the air cleaner to be burned in the engine.

You need to bore a 1 ¼” hole for the vent. Placement is not critical, just keep it under the hump in the trunk floor. I flipped my tank upside down and set a couple of speaker magnets near the hole to be cut. This prevented dropping metal shavings in the tank. Also, deburr the edges before installing the grommet.

Now it is time to mount the tank and hook everything up, hopefully for the last time. Do not install the sending unit yet.

The last thing to do is reroute your fuel lines and wires to the sending unit. The Maverick & Comet plug has 2 wires going to it. The Mustang sending unit only has hook up for 1. Cut the plug off the wiring harness and strip the bare the ends of insulation off the ends. Turn your key on and watch the gas gauge. Ground one of the 2 wires. If the gauge does nothing, ground the other wire. The gauge will go to full when one of the 2 wires is grounded. You will hook this wire to the connection on the sending unit. The other wire will be grounded to the gas tank. Make sure you have a good ground. Many electrical problems can be traced to bad grounding. Hook all the wires up, ground the sending unit to the tank, and check it out. Now is the time to check, not after you fill it up. If everything checks out ok, install the sending unit.

That is about all there is to it. I thought it was a fairly easy mod and the benefits are well worth it. Now get rid of those girly 2” pipes and hang some manly ones in there. If you have any questions you can Email me at

Good Luck,