mustang fuel tank & sending unit solution

[55metalmonkey]

Hi all,
I've received a couple PMs regarding my fuel tank install, specifically the sending unit mods I did on my 55 so I figured I should start a new thread with some pics to show how I did it. This is just my solution and I don't claim to be an expert just thought I'd share this, there may be better ideas out there so feel free to chime in.

I'll start from the very beginning.

For those that are new and wondering why anyone in their right mind would put anything f*rd in an old Chev/GMC the answer is that it is common to relocate the gas tank from behind the drivers seat to the rear frame and the 64-68 (16 gal) mustang tank or 70's 18 gal tank fits near perfect with just a few mods.
Partially so you get some extra room behind the seat(s) and so you don't have gas fumes in the cab, but I did it mostly for safety, I always jokingly say I'm not worried about getting killed in a crash, I just don't like the idea of living through it

I used the 16 gal tank and mounted it on the top side of the frame since I had the clearance and I also don't see this truck going on long hauls very often. I have seen a couple guys go for the 18 gal tank to get some extra range in which you will need to mount it in between the C channel of the frame rails or modify the box cross members if mounting it on top since the 18 gal is a couple inches taller.

I don't have pics of everything but it was fairly straight forward. The first thing I did was to drill and punch out the top rivets and cut out the lower part of the rear cross member where the rear spring perches are, keeping the cuts close to the frame. Some people drill and punch the lower ones as well to get the cross member out intact and then use grade 8 bolts to re-secure the perch but I decided to leave the lower rivets alone to save a step since it doesn't affect the rest of the mods.

The cross member was pulled out and flipped so the hump was facing down then positioned as far back on the frame as I could then cut/ shaped to fit and welded back in (flipping the cross member gives you enough material to weld it in since the upper and lower frame rails are different lengths.
If you were installing the 18 gal tank inside the frame rails I would recommend having this piece removable so instead of welding this in you would need to box the ends and weld in nuts so it could be bolted and removed down the road if necessary for maintenance.... it is a F*rd part in a Chev after all so it is the most unreliable piece

Since I installed mine on the top of the frame I had to grind the top of the frame for clearance, 1/4" per side and also the front end of the lower edge of the frame about 1/8". I just kept fitting the tank in the hole until I was happy with the fit.
Again, If you were going with the 18 gal in between the frame you would only need to grind the lower edge.

The tank is only seam welded sheet metal ad designed to be supported all the way around since it will hold roughly 120lbs of gas full so I had to build and weld a frame for the tank using 1"x 1/2" heavy wall rectangular tube. Then I drilled and tapped the tube so I can bolt the tank in later. Since the frame isn't completely flat after the rear turn-up for the rear axle I added a piece of tube to the bottom of the tank frame so it would sit level and then positioned it and welded it in.
For the 18 gal tank in between the frame rail you would want the frame to slide in and bolt in from underneath and position it so the rear cross member can be bolted in.

All of this was fairly straight forward but the sending unit presents its own challenges, more to come.