by Frank Swygert
The 64-68 Mustang gas tank has become a “universal” tank for many hot rodders. It’s easily adaptable to many Rambler and AMC models when there is no replacement available. The best thing is the stock Ford Mustang sending unit is compatible with AMC gauges from the 50s all the way up to 1976.
The first thing to consider is the size of the tank. From the outside edges of the flange the Mustang tank is 32-3/4″ (some sources list 32-5/8”) wide x 24-1/2″ front to back (of car) x 7-1/2″ deep (some sources list 8”). The size of the tank less the perimeter flange is 30-1/4” wide x 21-3/4” front to back. This tank has a 16 gallon capacity, enough for most. There is a higher capacity 22 gallon version that is 9-3/4” deep.
Measure your original tank. If it is no larger than the Mustang tank you can use it. It doesn’t matter if the Mustang tank is smaller. The flanges around the perimeter can actually be bent up or down to gain some more room if necessary, about 1-1/4” on each side. I wouldn’t cut them off – you could cause a leak.
There are several ways to mount the tank. Mustangs use the tank as the trunk floor. Some simply cut a 30-1/4” x 21-3/4” hole in the trunk of their Rambler and drop the tank in. It is secured around the flange with screws. I don’t recommend this – not unless your trunk floor needs replacing anyway. Note that the 16 gallon tank leaves a relatively flat floor, the 22 gallon model extends up into the trunk about 1-3/4”.
It’s just as easy to suspend the tank under the floor with the original tank straps. The flanges may need to be bent for the straps to go around it, and the straps may need to be altered in length.
Another way to mount the tank is to use the original mounting flange, but bolt it to the floor with the tank under the car with just the bolt heads inside. To do this first drill four bolt holes in the trunk matching the location of the holes in the tank flange near the corners. Put these four in the holes in the trunk from the top and put nuts and lock washers on them under the floor. These will be used to hold the tank up while the others are put in. You might want to do all of them that way. If you’re concerned about pulling too much on the flange install a second bolt to act as a stop. I suggest using carriage bolts or round Phillips head machine screws.
So what about the filler neck location? It will work for a few models, like the 64-69 American, but not for most.
The simple solution is to mount a gas cap filler right on the neck. Two problems – if the gas caps doesn’t seal well fumes can get in the passenger compartment, and you have to open the trunk every time you get fuel. Spills can occur when filling, and you have to be careful how you pack the trunk so you don’t block the cap. If you cut the floor out this is easy, otherwise just cut a hole for the filler neck to come up through the floor. This is far from ideal, but workable in a pinch.
By far the best solution is to remove the filler neck from the tank and weld a cap over it. If you don’t weld or have a friend who can weld sheet metal, a welding shop won’t charge much. You will also need to weld on a new filler neck in the appropriate location. You can find different pre-bent lengths of exhaust tubing at most parts stores in various diameters. Most will use a 1-1/2” or 2” filler.
You can screw a plate over the original hole, but you must use a gasket (rubberized cork preferred) and a screw every ½” around to make sure it seals. In this case the plate should be about 1/16” thick (14-16 gauge) so it will be stiff enough for a good seal. Use ½” self tapping screws. Be careful not to strip the holes as you’re just going into thin sheet metal. Pre-drill the holes in the plate slightly larger than the screws so you’re just self-tapping into the tank metal. It is possible to bolt a short neck on with a gasket also. Tanks Inc. (https://www.tanksinc.com/index.cfm) has a good selection of bolt-on filler necks with gaskets and backer rings. You can get to the back of a filler to put a nut on, you can’t for a cap. Note that bolting on works, but does leave a place for possible leaks in the future.
Tanks Inc. sells various gas tanks and other items, including universal straps – anything you might need for a gas tank. Speedway Motors also carries a lot of gas tank accessories and tanks.
While I’ve been talking about Mustang tanks, any gas tank can be used. Some people have mentioned using Chevy II or Chevelle tanks, for instance. Those will work, but the sending units won’t be compatible with AMC fuel gauges. You will have to modify the sending unit or use an under dash aftermarket gauge compatible with the tank unit. This isn’t an issue with Ford tanks. Other options from Tanks Inc. include a 41-48 (33-1/2″ x 19″ x 8″), 49-51 (24-1/2″ x 23-1/2″ x 7-3/4″), and 55-56 (23-1/4″ x 30-1/2″ W x 7-1/2″).
