You are loosing the picture. The inner tube is the vent for filling, it allows air to escape during the filling process. With it not being connected at the filler neck, fuel is enterring it and blocking the venting process. Connect the vent line to filler neck first, then connect filler hose to neck and stuff the two hoses into the tank. All will work.

Thanks... will try again.

Heres a new one for the books. See if you can make any sense to this. Have taken the filler pipe and vent tube off so many times we can do it in our sleep. Vent tube slides into a flange at the top of the filler tube neck. The other end goes into a tube inside the tank. Every things assembled as it should be..no kinks. Same situation, 3 gals in and gas pump clicks off. I tried to fill the tank from a 5 gal gas can via a siphon and it would only take 1 gal, and very slow fill. Had to stop many times to let the gas drain in. The filler pipe filled up with gas and would not drain in. Filler pipe filled up to the cap and stayed there. Had to siphon some out. It was like the tank was full, but I know there was only a max of 5 gals in it. Any suggestions ? Everything else works fine. Another thing, the gas gauge registers all over from 1/2 tank to full to 1/4 tank, so I really don't know how much gas is in the tank. Front tank gauge works perfectally fine.

I think your rear tank is totally full....

Went back and skimmed all the posts again. I don't see where you have done any fixing on the front tank? Have you dropped the front tank and had a look? Remember as I said in post #6, BOTH in-tank pumps must be functioning in order for the switching valve to operate... So even a new switching valve will not work if either of the tank pumps are not working. The system could still be pumping fuel from one tank to the other.

One possible cause... Inside the tank, on the sender assembly there is short a rubber tube which connects the tank pump to the metal sender tubing. If that rubber tube has rotted away then tank debris will be sucked into the system and plug up the selector valve.

Had the front tank down , took out the pump and everything ok, so re-installed it. It was replaced by ford 2 years ago. I don't think the rear tank is siphoning gas from the front as the gauge is stable and not going down. As a last resort, I am going to let the rear tank run out of gas and see how many miles it took. This will give me an idea how many gals. are in the tank at the time of the fillup that clicks off the pump. The tank holds 19 gals. This is really the last resort. Everything is where it should be in the fill tube and vent line placement. There really isn't much else to check. Thanks for your time and info. Roland

Engine died after 22 miles which would be about 1-1/12 gals. Fuel gauge showed full. I know there was more than 4+ gals in the tank. It would start up again but I switched to the front tank as I was in traffic and didn't want to take chances. Any ideas what this sounds like ? Thanks.....Roland

Are you sure the connecting tube is installed on the sender?
It's the black rubber tube above the pump shown here:

http://64.13.91.137:86/F150/Sender.jpg

If missing or broken then that would cause a mostly full tank to suck air.

I may be wrong but I believe alcohol in today's fuel will eat away the original tubing. When I did my rear tank the tube was completely gone from the sender. It was dissolved int an unrecognizable blob of sludge in the bottom of my tank.

have to ck everything again. Enclosed a page from the old 86 Ford manual w/description of the placement of the vent tube etc. Hope you can add it to your site for future use.

Here's a more detailed view. For your reference

Duat fuel tanks
 

Finally , a cure. The vent hose just slides up into the filler tube. No hookups,just in filler. The tank was full. The problem was a faulty sender on rear pump # 2. Tank now fills normally, both tank pumps work fine. I keep track of the mileage so I know when to fill the rear one. A little inconvenient but I'm not going to pull the rear tank down again. The front sender registers on the gauge just fine. I get 14 mpg and the tanks capacity is 19 gals, so Now I have to do the math on the back tank. I want to thank everyone for their assistance. You were a great help. Thanks again.
Roland