Fuel tank sender, can't get it to read "full"

[two-bit]

Hey ya'll,
I have tried all the tests and still can't get the fuel tank sender in my F-350 cattle truck to register "full" on the guage.
I've got the 21.5 gallon, in cab, tank. I know its full, but the guage only reads 3/4 full. I tested the float, the sender, and the resistor voltage. it all comes out fine.
Any guesses as to what might do this. I considered the fact that since the sender is out of a 19 gallon tank that it might screw up the float movement. But the tanks are the same "hieght", so i don't believe it will.
Am i wrong? Could i just bend the rod on the sender to trick it into saying full?
I can get it to say "full" when i operate it by hand out of the tank.
Any guesses?
Two-bit

[kid]

A float that sounds like it has a little too much weight for the float to lift. It might have a little fuel inside of the chamber. If it is a cork or neoprene foam float they can get fuel saturated and slowly sink. If you bend it then the other end will not read right.

Do a check for the float being wet internally. And do a search for fuel guage on this site. There is info about adjusting the guage.

[fordman]

i read that some people say to take off the anti rattle rubber to make it less heavy if you have one on the float. or you can adjust the voltge to the guage.

[kid]

I am going to try something with my 3/4 full float. It will be an engineering study of the values needed to drive the guage to full compared to the floats reading of full and see if I can come up with some useful data for here.

[gjc12]

wait...the needle is supposed to go all the way up to the F??

[68F250]

10 ohms should get the gauge right on the "F" mark. Try substituting a resistor for the sender, give the gauge enough time to climb up to full.

[71 LONG BED]

It must be a '71. Look on the back of your gauge pod and find the adjustment. Fill the tank and adjust to full. It will also adjust your temp and oil gauges if you have them. Almost every '71 I have heard of this same problem (including mine).

[kid]

My 68 SWB had the problem. My 69 F350 has the problem and a friends 67 has it too so it is not just 71s.

[Big D's 69]

Yeah my 69 is the same way. Not gonna go throught the trouble of fixing it since I am replacing the tank with a fuel cell and the guages for digital or aftermarket. Then I know it will be right. But it dang sure reads right when it says empty.

[71 LONG BED]

I'm glad we '71's aren't the only ones.

[two-bit]

Hey Longbed,
Its actually a '72, but the parts are prolly all the same.
I am going to compare the angle of the sender rod to another one to see if it is bent. A guy i work with had it happen to him that the rod got bent and it wouldn't read full either.
Otherwise i will check for the adj. on the guage itself.
Thanks all,
Two-bit

[Faltura]

I have a 72 F-350 and my gas guage only goes to 3/4. I tried changing the dash voltage regulator and no difference. Can anybody tell me anymore about this adjustment screw behind the dash pod? My other guages don't work right either. It looks like my amp meter does not work at all

[FORDification]

Read this thread:

http://fordification.com/forum/viewtopic.php?t=9698

[scott]

I had the same problem until this afternoon. Followed the tech directions found on this site and cured it. The sending unit is easy to dismantle and a couple swipes on the pickups with crocus and its fixed.

[erikhillard]

I wish the pics were still on that thread.