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1975 F250 Fuel Tank swap from 19gallon to 38 gallon

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CoupeBoy
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1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #1 by CoupeBoy » Thu Mar 17, 2016 2:27 pm

Slowly but surely I am upgrading and replacing parts on my '75 Crew Cab
1975 CCSB -- War Hog -- FordSix Forum

I am replacing the rear original rust filled 19 gallon tank with a 38 gallon replacement.

I ordered mine off eBay for $106 including free shipping.

But you can order it from other places as well.
This is the same model that I have, but I paid nowhere near this amount.
Spectra Premium Fuel Tanks F26C -- Summit.com $183.97
LMC Truck has one of their own too.
38 Gallon Extra Capacity Gas Tank 1973-79 F100 - F150 - F250 -- LMCtruck.com $199.95

Last weekend I started the gas tank swap by pulling the original bed off of it.
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And there is the problem tank.
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Immediately I noticed how badly damaged the leading corners are. Somebody beet the snot out of those corners to get this tank installed.
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I started by pulling the sender unit pigtail.
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Then I removed the fuel line from the sender unit.
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I supported the fuel tank with a jack and custom holding block.
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While I removed the bolts that hold the lower tank straps, these two at the front.
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And these two in the rear.
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Much later I went back and removed the nuts from the bolts that hold on the top straps.
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I used the grinder with a twisted wire wheel to clean 3 out of 4 straps, I'm not sure why I forgot one. I'm not going back for it, because it needs to be replaced anyhow.
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I cussed and swore at this tank trying to get it out of the frame. The tank lip is wide enough that it can sit enough that if the lower straps fail, the tank can/will sit on the inner lip of the frame rails.

I tried to take it out from the top, I couldn't get enough angle to lift it out, the leading corners that were already banged up had 'interference' with the brackets and bolts that are supposed to be holding the box in place. These guys.
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Since the tank was coming out anyhow, I grabbed a standard claw hammer and used the head of it to pound down the corners of the tank a little more. You can see my additional damage in the side by side picture.
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Then I realized I was doing it wrong. The trick to getting the tank out is to slide it all the way to the driver side and the passenger side fuel tank lip slides right past the frame rail lip and you can drop the tank out, one side at a time. I know I took a picture of this process, but I *think* my daughter may have deleted them when she was playing with my phone this morning, because I cant find any of them.

At this point, the tank is out. I rattle canned on the straps with some duplicolor primer and paint (black)

I tried to slip the new tank up into place the same way the old one came out, you can see the interference on the driver side between the box bolt down bracket and the fuel tank cab corner.
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Physics is against me.
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With that interference issue, I can't quite get the new tank flange to slide past the lower frame rail lip.
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I see my options to be.
1. Cut the brackets off the frame.
2. Trim the brackets until they no longer contact the tank.
3. Remove the brackets, then make new brackets that can be bolted or welded to the top of the frame, the extra 1/4" may be enough to clear the tank.
4. hammer in the corners of my brand new shiny gas tank like the original tank to clear the brackets and bolts.

I am inclined to the options in this order.
2, 1, 3, and last 4

When I removed my box, there was only 6 bolts holding it in place, the back 2 box bolts were missing. So I know I would be 'OK' with only 6 bolts holding the bed in place.

I'll update again when I know more..
1968 Mustang Daily Driver Rebuild (on hold for the Season 3/1/2015)
1963.5 Falcon Convertible Build (just getting started 3/15/2015)
Case 1830 Skidsteer FordSix Repower Thread (started 4/4/2015)
1970 170/C4
1967 200/C4
1965 240/bellhousing/flywheel/clutch/3.03 bell pattern
1975 250/flexplate
1975 300/flywheel

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CoupeBoy
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Location: Fargo, ND
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Re: 1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #2 by CoupeBoy » Thu Mar 17, 2016 2:28 pm

I got up early, it was a balmy 6f outside and a toasty 20f inside, it's 4:50am CST.. which during the work week is about the only time I get 'shop time'
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Due to my propane company still not having installed a regulator for my real furnace, I have a 7500w (220v) hanging electric heater, and a propane ice house heater, which I believe is about 80,000BTU.

I fire them up and get to work.
I throw a 4" cutoff wheel onto the grinder and cut off the box hold down bolt tabs.
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Passenger side.
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I am going to have to clean that up a little bit with a grinder wheel.
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Driver Side turned out much better.
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Big open hole, ready to recieve.
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And the new tank fits right in, now that those tabs are out.
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The kit came with longer hold down bolts and spacers, so I reinstalled the straps with the new bolts.
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The problem is with the provided spacers, the tank sits up way too high. Whether those brackets are on the frame or not, the reinforcement bar across the bottom of the box/bed still has to lay across the bed.
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I thought about this 2 ways.
A. How much space is there between the lower edge of the frame rail and the tank flange. I can lower the tank this much.
OR
B. How much too high is top of the tank, if I want the tank to sit flush with the top of the frame rail.

To solve A, I reached under the frame and stuck a tape up from the bottom at the front and rear of the tank.
At the rear, it is about 3"
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At the front it is about 2"
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It was about at this point, that I remembered that the original fuel tank spacers were different heights.
Short ones (1.25") in the front, long ones (2.25") in the back.
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FWIW, the kit I bought came with (4) 5.5" spacers and matching bolts.

Measuring method B
I laid a flat board across the top of the new fuel tank and measured the distance from the bottom of the board to the top of the frame rail.
It showed that I needed to lower the tank about 2"
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I have a few more things to measure.
I'd really like to get the tank down to a height that allows me to use some bolt brackets, even if they need to be bolt on. Maybe design some short ones that are barely big enough to capture the bolt.

I also know that I do NOT need to drop the gas tank all the way down for clearance between the top of the fuel tank and the bottom of the pickup box.

For now, I'm going to run past the local hardware store and get some bolts that are long enough to keep the fuel tank flange 1/4" above the lower frame rail. I'll make some steel spacers to work with the new bolts. I want to keep the gap to allow any small rocks or water to drain/fall.

Since I have 2" of space and I want 1/4" clear space, that means I want to have spacers that are 1.75" longer than the ones provided.
5.5" + 1.75" = 7.25" (new spacer length)

If I was really on my game, I'd bend a C-shape piece of flat steel with 7.25" OD, and then cut down spacers to fit the ID and then run bolts through the whole ordeal. That would give me strength and a stone shield.

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Re: 1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #3 by CoupeBoy » Thu Mar 17, 2016 2:30 pm

The other part of the swap that is going to be trouble..
The sending unit..

I pulled the one from the old tank.
This thing looks nasty and crud covered.
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The kit came with an extension pipe for the pickup tube, an new lock ring, an extension wire, and some scotch locks.
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I am NOT using those scotch locks, in my experience those are only good for creating questionable connections and accelerated corrosion on the wires, I plan on soldering it and then using shrink wrap on the connections. That is the easy part. The hard parts are going to be figuring out how long the pickup tube needs to be, and if there is a preferred angle that it should be. And figuring out how long the float lever should be so it operates on full range.

I thought I'd go ahead and wire wheel the crusty bits off the original sending unit, it was functional, so I planned on reusing it.

It cleaned up pretty well
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Except 2 things..
1. I broke off the bottom of the fuel pickup, probably not a big deal. I can most likely glue it back on.
2. The float has a crack in it and was retaining gas.
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And the crack. I could probably find a way to solder this or foam fill it. Or find a suitable replacement made from something else.
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LMC and RockAuto both have sending units for about $40, locally o'Reilly's has one for $70.
I'm going to order a new one, but I'll continue using the original one for test purposes.

The other thing I need to fix/replace is the fuel filler and vent tubes.

Dryrotted, hardened, and cracked.
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Any suggestions on where to get replacements?
Are these off the shelf parts or will I need to go through a vendor?

It was now about 6:20am and time to head back into the house, the kids need to be woke up for school.
The heaters had been running the whole time and the shop was up to a balmy 40f.
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Re: 1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #4 by CoupeBoy » Thu Mar 17, 2016 2:31 pm

While I was working on other stuff, I poked a hole in the old tank.
I tried non-destructive means of pouring the gas out, but then I realized that I'm never using this tank again, so why bother keeping it nice.

I had already ripped a hole in it during one of my less graceful attempts to remove the tank, so I took a punch and a hammer and added this second hole in the same corner.
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And the gas that came out was disgusting.
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Back in the olden days, I had an uncle that used to pour his gas through cheese cloth when filling his tractors.
But I didn't have any...
So I grabbed what I had.. steel wool, I packed some down the funnel and started pouring.

Rust sediment
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And when I was done.
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I could hear more chunks swishing in the fuel that was left in the tank. I'll most likely keep the fuel for fire starting, I've got an old tractor rim that I use for bonfires in warmer weather. Or washing parts..

until next time..

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Re: 1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #5 by CoupeBoy » Thu Mar 17, 2016 2:32 pm

No work Wednesday morning, my 7yr old daughter had a night mare at 5:30am and I stayed inside after that.
Wednesday night I got back out to the shop and worked on things a bit.
Earlier in the day I had stopped at a local hardware store called Mac's and picked up some bolts/nuts/steel square tubing.
The longest 3/8" bolts they had were 8", I had been hoping for 8.5" But I think the 8" is going to work.
I removed the original 5.5" steel tube spacers and the 6.5" 3/8" bolts
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The tank now sits a lot lower, but something wasn't quite right.
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The passenger side looks pretty darn good for clearance.
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But the driver side is off by quite a bit, it just isn't sitting down low enough.
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The culprit seems to be the front flange on the tank, it has a pretty good bend in it.
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I pulled out the tank and used a pipe wrench to straighten it out.
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It should set level now, I didn't finish/retest the fit because I moved on to removing the rivets for the rear shackle brackets so I can install the flip brackets.

And that was when my grinder died.
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It was a cheap Harbor Freight one that I bought so long ago that I don't even remember when it was, seems like forever. I got my $9.99 out of it.

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Re: 1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #6 by CoupeBoy » Thu Mar 17, 2016 2:33 pm

I'm still working on my spring swap and grinding the brackets off the frame rail from the previous owners welded on bumper.
And I'm still waiting on the new fuel sending unit that I ordered from RockAuto.

This morning I stumbled upon this video which should help me get the fuel pickup tube into the correct location.
https://www.youtube.com/watch?v=FUNMcLN3xLc

One thing that just isn't abundantly clear to me is how to adjust the float to read properly, full/empty
To my armchair engineering brain, I want/need to keep the electronic portion of the sender in the original location.
If I did no other changes, the tank would read full when full, and empty when half empty.
With 2 tanks this wouldn't be the end of the world, run it dry, then change over.
which would work if it was just me and I planned on keeping it forever. Quirks, everybody's favorite car has one or 2.

But I don't want to have to keep a specific list of "do and do not's" to operating this truck.

So my idea is to extend the float arm, not bend it, not move the electronics of the sending unit/float

So I am going to set the fuel pickup tube like the guy did in the video.
Then, I will extend the float arm so that the float almost sits at the bottom and as long as I only extend it straight, it *should* still show full when full, and empty when empty.

There are a few people that said using a 33 gallon sending unit would get you 'close enough' by leaving 5 gallons sitting in the bottom of the tank when on empty, but they recommended extending the fuel pickup still.

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Re: 1975 F250 Fuel Tank swap from 19gallon to 38 gallon

Post #7 by CoupeBoy » Thu Mar 17, 2016 2:34 pm

At first I thought to cut and extend the new float arm by using a piece of wire coat hanger, so I cut some and test welded it.
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That looked like crap on toast..
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So I hit it with a grinder to clean it up a little bit.

Not any better.
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And then it occurred to me.. why not simply make a new float arm from the wire coat hanger.
5 minutes and a pair of vice grips... presto.
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To keep the float on, I hammered it flat, and then I stuck a booger weld on the end.
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It sits right down into the low part of the tank with the pickup tube.
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In these pictures, the truck is running and pulling fuel from the newly installed tank/sending unit.
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The last things I have left to do is make the new spacers for the extended bolts, and get some new tubing for the filler tube.
That filler tube (2.25" ID) is fairly expensive for a piece of hose, locally about $25/ft and it is sold by the foot, which means $52 for 2ft of hose. I need to do more shopping.

Here it is again.. my "helper" in the first pic.
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