All we’re trying to do is give air that’s inside the tank a better way out, as incoming fuel displaces it. The actual process is easier to do. All you do is remove & gut your filler neck, by putting a fitting near the top of the filler neck for a 1/2” or 5/8” hose. Put a plastic elbow in place of the rollover valve on top of your tank, with a hose barb the same size as the fitting on the filler neck, and run the right size of hose between these fittings. Before you even get started, you may want to go to the www.transferflow.com website, and look at the filler necks for ‘94-’97 Fords. This is what I tried to copy. It may be a good time to mention that these kits would be the deluxe way to go, if you want to spend around $110 per tank. Just think ahead and try to keep the fittings fuel & air tight. These instructions will apply to F350 4x4 Crew Cabs. The other models should be similar, if not exact. 2wd trucks have their tanks mounted slightly different from 4x4s, but the mod is still the same. Go out and pull off your fuel caps, and look at where the cap threads into the neck, and look down the inner part of the filler neck. You’ll see a kind of crescent shaped slot in the bottom of where the fuel cap seats. This is where the air inside the tank comes out as fuel goes in. The outside filler neck is metal, but there is a rubber inner hose 1” in diameter that the fuel goes in. This hose runs all the way into the tank. As fuel travels down inside the rubber inner hose, air is supposed to come through the passageway between the inner hose and the outer metal tube. When the foamy #2 diesel fuel does reach a certain level in the tank, it won’t allow air to escape. This design flaw is what makes the tanks so darn hard to fill. There is a little vent with a check ball in it on top of the tank. It allows a tiny amount of air to get in, but not much. It’s called the “rollover valve”. If your vehicle rolls over the check ball is supposed to close off so no air can get in the tank, theoretically preventing fuel from escaping. Don’t make any bets on that. I removed these & replaced them with a plastic elbow to hook up a hose to. I did my front tank first, because it was the easiest to remove the rollover valve. No need to drop the tank for that part of the mod. You can find another filler neck and modify that one so there’s no down time on your rig. I found out the filler necks out of gas rigs are similar, and can be made to work. Or do like I did, and do the front one first, while driving around on the rear tank. You’ll need to run the rear tank either very low or empty anyway, because it has to be dropped to get the rollover valve out. As long as you switch the tank over quick enough, you can run our PSD’s out of fuel, without the problems associated with “normally injected” diesels. You’ll have to run the back tank empty or at least very low on fuel, whether you modify or use Transferflow’s. It’s very difficult to wrestle around with fuel in it.

Stuff you need to do this mod with
2 fittings for 1/2” hose that can be attached to the filler neck. These can be 90 degree brass/metal elbows that have threads on one side, or whatever, but must have a 1/2” or 5/8” hose barb on the other end. I scrounged mine off of old Mazda air box, but this is a probably a more expensive way to go.
6’ of 1/2” I.D. fuel line. I used the clear stuff from Ace Hardware.
2 nylon/plastic elbows. Again, one end will have a 1/2” hose barb, while the other will need 3/4 NPT threads. Found these in the sprinkler section of a home improvement store.
4 little hose clamps to fit over the 1/2” fuel line.
Some bolts about a half inch longer than the stock bolts holding the back tank in.
Some strips of rubber about 1” wide, 1’ long, & 3/8” thick.
Note: The 1/2” stuff can be substituted with 5/8” fittings and fuel line. It would work even better, but 1/2” stuff is far more available in my neck of the woods.
A 3/8” round file.
A set of tanks with cutting and brazing tips (oxy-acetyline setup).
Some decent size drills, and a couple of screwdrivers.

The hardest part, modifying the filler neck. Remove the filler neck. There are 3 sheet metal-type screws under the fuel cap, and a hose clamp that clamps a large rubber hose from the tank to the bottom of the filler neck. There will be another hose clamp holding the filler neck to a tang on the inside of the bed also. It’s not necessary to remove the large hose from the tank, but you will want a rag handy to stuff in the hose to keep dirt out. You can also stick an old lid off of a rattle can of spray paint over the hose end. When you’ve got the filler neck out with the rubber inner hose trailing out of it, you’ll need to remove that inner hose. I stood on the trailing end, held the filler neck very firmly, & pulled the rubber hose out. Now you’ve got a metal filler neck, with a metal ring around it where the old rubber hose was hooked up to. The hardest part of the whole thing was removing this metal ring. I knocked mine loose with an old wooden broom handle, tapped it around the bend in the neck, and drove it down towards the bottom end. There is a taper formed on the bottom end that won’t allow you to just drive it out, so you have to be creative here. I used my cutting torch turned down way low. This is very thin metal, so be careful with the heat from a torch. It may be possible to cut some slits in that ring with a Dremel tool and do some twisting with needle nose pliers, but I didn’t have my Dremel tool at that time. However you can do it, remove the metal ring without hurting the filler neck. If you find an easier way to do it than how I did, please let me know about it. After that’s done, you’ll need to put a fitting on the upper part of the neck for a 1/2” hose. I put mine on the side of each neck, about 1 & 1/2” below the flange the 3 little sheet metal screws go in. Drill a hole of the proper size in the location you want the hose fitting to go. Put some thought into this. This hole needs to be above where the end of a fuel pump nozzle would extend. It is possible to put your fitting where you’ll never be able to get a hose on it. Drill a hole in the place where you want the elbow/fitting at in the filler neck, and braze the fitting. Some people have simply threaded their hose barb/elbow fitting into the hole that they drilled, but I wasn’t convinced it would stay liquid tight. Mine does not leak. My fittings were taken off of old air cleaner boxes from Mazda cars. They were fittings for emissions hoses to hook up to. I cut them off of the air box & brazed them to the filler neck, at a location similar to where Transferflow’s fittings are. A metal or brass elbow with a 1/2” hose barb will do. Now let’s look at the top of our gas tank. There are 2 fuel lines for each tank, and the sending unit on top. Locate your rollover valve & remove it. The rollover valve is a white plastic thing sticking out of a rubber grommet on the top of the tank, just about square in the middle of the tank. One end of the rollover valve will have a small diameter hose about 1’ long clipped to the frame. Pull the hose off the frame, then grab the rollover valve & wiggle it up and out of the tank. This is easy to do on the front tank, but you’ll have to drop the rear tank to do that. You need a fitting for the tank with 3/4 NPT threads to go in the grommet on top of the tank, and a 1/2” hose barb on the other side of the elbow. I modified the very top portion of the threads by filing a groove for the fitting to seat in the grommet as the rollover valve had. I just used a 3/8” round file, and made the groove about as deep as the threads and about 1/4” wide. The elbow seats nicely in the grommet this way, just like the old rollover valve did. When you put the elbow in the grommet, coat the threads with either thick oil or grease, so it goes in easier. I now recommend threading it into the grommet. I just pushed my first one in, but it also pushed the grommet inside the tank. I wound up dropping the front tank to fish out the grommet. Oh, well. Slide one end of your 1/2” I.D. hose over the hose barb on the tank, & put a clamp on it. Route the hose up along side the big hose going into the tank for now. Put the modified filler neck back on the truck. Hook up that big rubber hose to the end of the filler neck, & clamp it. Attach the fuel cap end with the 3 little screws, and put the clamp on that holds the filler neck to the inner part of the box. Slide the other end of the 1/2” hose over the fitting you painstakingly put on the filler neck, and put a hose clamp on it. You now have one side done, & your tank should fill much faster, and fill up completely.
Some thoughts on this mod:
When you drop the tank(s), you don’t need to unhook either of the fuel lines just to put the elbows in. Ditto for the sending unit. On the back tank, I had to put some strips of rubber mat material (3/8” thick) on top of the tank, to space it down a tad. The new elbow with the hose barb sits higher in the grommet than the rollover valve did. The elbow would rub on the underneath part of the bed without the extra room. This also necessitates getting slightly longer bolts for the straps or spare tire carrier to hold the tank up. I’ve heard Transferflow’s kits come with this stuff, as it is necessary to do the same thing with their setup too. Leader used strips cut from an old truck mud flap. All this sounds like a hassle. It took me no time at all to do the front tank, even with the fishing trip for the grommet I pushed in. Figure 3-4 hours for each tank depending on how you’re set up for tools. The back required a trip to the hardware store for longer bolts. I killed more time than most would on mine, but I like spending time with my truck, just not at the pumps. Transferflow’s kit is sounding pretty good by now, I bet. I just like to try doing it myself, and have probably less than $40 into it.

 

good write up thanks for the input