38 Gallon Rear Tank and 1984 Hot Fuel Handling System

[JunkCollector]

I'm planning on upgrading my tank in the rear of my '84 F350, I've asked around in a few groups and did a fair amount of research and came down to these questions.

1. Which tank will work with a 1984, with electric pumps? F26c (listed as correct for 1984 on rockauto) or F26d (listed for 1985 trucks)

I ordered a 1984 sending unit for my rear tank not realizing the amount of rust in it, and it fit but I can't use the tank because of the poor condition

2. Can the hot fuel system sending unit be correctly modified to work in the 38 gallon tank? There isn't much info on modifying the senders at all, and even less for the '84 electric pump trucks.

The 460 running one 19 gallon front definitely doesn't have the range I want, and two 19 gallons isn't that much better at 4mpg loaded. I use the truck for long-ish distance towing and will soon have it in a shop for a laundry list of work since its downtime season. I'd like to see how hard the upgrade is, if it's even worth it. I won't be carrying a spare under the bed, so that won't be a worry.

Thanks in advance, y'all!

 

[ArdWrknTrk]

There's not much to extending the pickups in these trucks to the bottom of a deeper tank.

I might want to add a piece of Holley Hydramat to the pickup, but it's expensive and all these trucks worked fine without it.

It's not like the Aeronose trucks with a FDM that sits in the neck and has to reach to the bottom of the tank.

In 1985 trucks went to in-tank EFI pumps and have a larger (4"?) bung.

So, if you already bought a new sender for an '84 I'd think you need the 2 1/2" bung found in the F-26C tank

There are some threads about using a 33 Gal Bronco tank and some threads mentioning the metal tank or big poly tanks intended for diesel.

I can help you search for more information on conversions, but if you're only wondering what the difference is, it's that '85 & up have a bigger hole and retaining collar.

[ArdWrknTrk]

There's not much to extending the pickups in these trucks to the bottom of a deeper tank.

I might want to add a piece of Holley Hydramat to the pickup, but it's expensive and all these trucks worked fine without it.

It's not like the Aeronose trucks with a FDM that sits in the neck and has to reach to the bottom of the tank.

In 1985 trucks went to in-tank EFI pumps and have a larger (4"?) bung.

So, if you already bought a new sender for an '84 I'd think you need the 2 1/2" bung found in the F-26C tank

There are some threads about using a 33 Gal Bronco tank and some threads mentioning the metal tank or big poly tanks intended for diesel.

I can help you search for more information on conversions, but if you're only wondering what the difference is, it's that '85 & up have a bigger hole and retaining collar.

Spectra also offers the LO26A fuel pump extension kit for $31at Summit.

But it's basically an assortment of tubes and clips and bushings that seem like a catchall to fit any of their deeper tanks.

I'd probably just get a piece of tube and swedge it in there...

[JunkCollector]

Spectra also offers the LO26A fuel pump extension kit for $31at Summit.

But it's basically an assortment of tubes and clips and bushings that seem like a catchall to fit any of their deeper tanks.

I'd probably just get a piece of tube and swedge it in there...

Thanks for the info, I'll probably end up running a 19 for now just to get it all working (it's been on the front tank for 20 some years and I doubt my shop would be ok with cutting up a sending unit) and upgrade later. Now I know which one to get and how in depth it'll be. Also thank you for the link for the extension kit, that helps a lot!

[ArdWrknTrk]

Thanks for the info, I'll probably end up running a 19 for now just to get it all working (it's been on the front tank for 20 some years and I doubt my shop would be ok with cutting up a sending unit) and upgrade later. Now I know which one to get and how in depth it'll be. Also thank you for the link for the extension kit, that helps a lot!

Glad I could help point you in the right direction.

I thought my truck at about 10mpg was expensive. I can't imagine 150 mile range at 4mpg....

What's the gearing in your D70?

[85lebaront2]

4 mpg? What gear is in yours? Darth always got a solid 10 mpg empty or loaded, 7 - 8 towing a 30 ft 5th wheel. This was still running the carbureted 460 and C6 and at the time still had all of the original factory exhaust system.

I agree with Jim, extending the pump mount down so the pickup is in the low point of the tank and hopefully a gauge sender that reflects the actual fuel level. I think I still have the original rear 19 gal pump and sender from Darth, but don't know if the pump is any good.

FWIW, after converting to EFI and E4OD, even with quite low compression (early large dish pistons and early EFI large chamber heads) Darth delivered 12.5 mpg on a long high speed (70 mph) run after the updates.

[ford4wd08]

4 mpg? What gear is in yours? Darth always got a solid 10 mpg empty or loaded, 7 - 8 towing a 30 ft 5th wheel. This was still running the carbureted 460 and C6 and at the time still had all of the original factory exhaust system.

I agree with Jim, extending the pump mount down so the pickup is in the low point of the tank and hopefully a gauge sender that reflects the actual fuel level. I think I still have the original rear 19 gal pump and sender from Darth, but don't know if the pump is any good.

FWIW, after converting to EFI and E4OD, even with quite low compression (early large dish pistons and early EFI large chamber heads) Darth delivered 12.5 mpg on a long high speed (70 mph) run after the updates.

Since we are talking about fuel tanks and getting more range for a 460, I have a couple of questions about my restore/build of my grandad's truck.

The truck came with only one side mount 15 gallon (or whatever it is) tank.

Since it was new it's had an aux has tank mounted below the flatbed as seen in this picture.

The way it was rigged up to use was having and electric pump mounted on the frame rail and pumped to the filler neck of the stock tank. It was done via manual switch that was easy to leave running.

How would you guys suggest managing this type of dual tank in more of an automated solution?

This tank is mounted lower than the stock tank and I would like to avoid anything like Ford's failure prone method with the switch on the dash solenoids etc..

Sorry, not trying to thread jack, just curious how one would run two tanks?

[ratdude747]

Since we are talking about fuel tanks and getting more range for a 460, I have a couple of questions about my restore/build of my grandad's truck.

The truck came with only one side mount 15 gallon (or whatever it is) tank.

Since it was new it's had an aux has tank mounted below the flatbed as seen in this picture.

The way it was rigged up to use was having and electric pump mounted on the frame rail and pumped to the filler neck of the stock tank. It was done via manual switch that was easy to leave running.

How would you guys suggest managing this type of dual tank in more of an automated solution?

This tank is mounted lower than the stock tank and I would like to avoid anything like Ford's failure prone method with the switch on the dash solenoids etc..

Sorry, not trying to thread jack, just curious how one would run two tanks?

Off the shelf: I don't know.

Custom (NERD ALERT!): Does the aux tank have a sending unit? If so, if one was skilled enough with electronics one could use a microcontroller (arduino, etc) or Op-Amp circuits to make something that would turn on the aux pump when the main tank got below a threshold but not shut off until it was nearly full (or another "higher" threshold), but only if there is fuel available in the aux tank. If going the analog op-amp route, you'd need a voltage comparator for the latter and a positive-feedback amplifier for the former (to give the hysteresis needed to prevent short-cycling the pump and control relay), plus some buffer amplifiers to keep the low-impedance sending unit circuitry from getting messed up by the added circuitry. On par with some of the things I had to make in my EET studies... Op-Amp circuits controlling a transistor controlling a relay... Fun...

Custom #2 (Less of a nerd alert?): use some relay circuitry (or an Arduino) and a push button with a kill switch. Time how long it takes a full aux tank to transfer (or whatever amount you generally would want to transfer at a time) and set the timer relay (or Arduino code) to match. Push the button, relay latches (wired in a latch configuration) until the timer cuts the circuit or someone hits the kill switch.

[ford4wd08]

Off the shelf: I don't know.

Custom (NERD ALERT!): Does the aux tank have a sending unit? If so, if one was skilled enough with electronics one could use a microcontroller (arduino, etc) or Op-Amp circuits to make something that would turn on the aux pump when the main tank got below a threshold but not shut off until it was nearly full (or another "higher" threshold), but only if there is fuel available in the aux tank. If going the analog op-amp route, you'd need a voltage comparator for the latter and a positive-feedback amplifier for the former (to give the hysteresis needed to prevent short-cycling the pump and control relay), plus some buffer amplifiers to keep the low-impedance sending unit circuitry from getting messed up by the added circuitry. On par with some of the things I had to make in my EET studies... Op-Amp circuits controlling a transistor controlling a relay... Fun...

Custom #2 (Less of a nerd alert?): use some relay circuitry (or an Arduino) and a push button with a kill switch. Time how long it takes a full aux tank to transfer (or whatever amount you generally would want to transfer at a time) and set the timer relay (or Arduino code) to match. Push the button, relay latches (wired in a latch configuration) until the timer cuts the circuit or someone hits the kill switch.

No sending unit in the aux tank.

I was thinking something along the lines of a timer. I have also used a speed switch in the past for another application, but could hook it up to a relay to trigger the pump at a certain speed and turn off when it's below that with a manual override.

[JunkCollector]

4 mpg? What gear is in yours? Darth always got a solid 10 mpg empty or loaded, 7 - 8 towing a 30 ft 5th wheel. This was still running the carbureted 460 and C6 and at the time still had all of the original factory exhaust system.

I agree with Jim, extending the pump mount down so the pickup is in the low point of the tank and hopefully a gauge sender that reflects the actual fuel level. I think I still have the original rear 19 gal pump and sender from Darth, but don't know if the pump is any good.

FWIW, after converting to EFI and E4OD, even with quite low compression (early large dish pistons and early EFI large chamber heads) Darth delivered 12.5 mpg on a long high speed (70 mph) run after the updates.

C6 power eater, 4:10 gears, a holley 670 truck avenger (on it when purchased) and a 2.25" dual through flow master super 10s that I need to change. It melted my carpet from the heat on the driver's floor. Can't imagine what the poor fuel tank switch valve is enduring.

Previous owner claimed he towed with it. All these issues and a failing cooling system flared up soon as I put a load on it so I'm saying he lied. 4 radiators five flushes and a thermostat later...

It drinks like nothing I've ever experienced. 10 bobtailing, 6 empty trailer, 4 loaded trailer. Secondaries stay open for 90% of its life even on smaller grades.

Extremely gutless thing, I'd always heard 460s we're powerhouses. I felt lied to when I put the 4400lb goose on it for the first time. Most I've had behind it is ~15000lbs and I wouldn't want that ever again. Usually pulls around 10k gross trailer weight.

E4od is in the works when compushift fixes their supply chain, and the timing adjusted to 12° base vs the factory 8. Really woke it up after that. Carbs been tuned on some, but I'm planning on installing a vacuum gauge and afr gauge to really dial it in. Eventually going TBI or stand-alone MPFI. But that's too big-money right now. I still have to switch the front hubs and rear end out to get the correct stud size to ditch these 16s. I'm ready for my 19.5s, dang it!