mustang fuel tank & sending unit solution

[55metalmonkey]

Hi all,
I've received a couple PMs regarding my fuel tank install, specifically the sending unit mods I did on my 55 so I figured I should start a new thread with some pics to show how I did it. This is just my solution and I don't claim to be an expert just thought I'd share this, there may be better ideas out there so feel free to chime in.

I'll start from the very beginning.

For those that are new and wondering why anyone in their right mind would put anything f*rd in an old Chev/GMC the answer is that it is common to relocate the gas tank from behind the drivers seat to the rear frame and the 64-68 (16 gal) mustang tank or 70's 18 gal tank fits near perfect with just a few mods.
Partially so you get some extra room behind the seat(s) and so you don't have gas fumes in the cab, but I did it mostly for safety, I always jokingly say I'm not worried about getting killed in a crash, I just don't like the idea of living through it

I used the 16 gal tank and mounted it on the top side of the frame since I had the clearance and I also don't see this truck going on long hauls very often. I have seen a couple guys go for the 18 gal tank to get some extra range in which you will need to mount it in between the C channel of the frame rails or modify the box cross members if mounting it on top since the 18 gal is a couple inches taller.

I don't have pics of everything but it was fairly straight forward. The first thing I did was to drill and punch out the top rivets and cut out the lower part of the rear cross member where the rear spring perches are, keeping the cuts close to the frame. Some people drill and punch the lower ones as well to get the cross member out intact and then use grade 8 bolts to re-secure the perch but I decided to leave the lower rivets alone to save a step since it doesn't affect the rest of the mods.

The cross member was pulled out and flipped so the hump was facing down then positioned as far back on the frame as I could then cut/ shaped to fit and welded back in (flipping the cross member gives you enough material to weld it in since the upper and lower frame rails are different lengths.
If you were installing the 18 gal tank inside the frame rails I would recommend having this piece removable so instead of welding this in you would need to box the ends and weld in nuts so it could be bolted and removed down the road if necessary for maintenance.... it is a F*rd part in a Chev after all so it is the most unreliable piece

Since I installed mine on the top of the frame I had to grind the top of the frame for clearance, 1/4" per side and also the front end of the lower edge of the frame about 1/8". I just kept fitting the tank in the hole until I was happy with the fit.
Again, If you were going with the 18 gal in between the frame you would only need to grind the lower edge.

The tank is only seam welded sheet metal ad designed to be supported all the way around since it will hold roughly 120lbs of gas full so I had to build and weld a frame for the tank using 1"x 1/2" heavy wall rectangular tube. Then I drilled and tapped the tube so I can bolt the tank in later. Since the frame isn't completely flat after the rear turn-up for the rear axle I added a piece of tube to the bottom of the tank frame so it would sit level and then positioned it and welded it in.
For the 18 gal tank in between the frame rail you would want the frame to slide in and bolt in from underneath and position it so the rear cross member can be bolted in.

All of this was fairly straight forward but the sending unit presents its own challenges, more to come.

[55metalmonkey]

Sending unit:
The stock F*rd sending unit uses 10-78 ohms which is backwards and out of range for GMs
Chevs/GMCs use 0-30ohm or 0-90ohm depending on if you have stock or aftermarket gauges

The other thing is F*rd uses a collar/ lock ring set up and GM uses a gaslet/ bolt set up.

I have seen people punch a new hole in the top of the mustang tank and weld in a flange to fit the GM sending unit so they end up with a stock GM sending unit for the gauge and use the stock F*rd pick up tube for the fuel supply.

My solution was slightly different. As I was looking over my parts it dawned on me that all I had to do was gut the float/ potentiometer from the stock F*rd sending unit and mount a GM one in its place which should work as long as the range of motion of the float stayed the same as the F*rd one did.

I started by mapping out the float range on a piece of poster board, marking the full and empty positions and started by cutting the wire & removing the F*rd float/unit from the pick up tube by bending the 3 tabs out to remove the potentiometer, keeping the backing plate spot welded to the pick up tube so I had something to mount to.

I had a new GM sending unit that came with a fuel cell from years ago that would work with my aftermarket gauges (0-90 ohms) so I removed the float so it wouldn't get damaged marking the full and empty position (just so I wouldn't flip it and bugger the whole thing up) and cut the potentiometer off the GM one leaving enough metal above so I would have room to use small machine screws to bolt it onto the F*rd pick-up tube backing plate. The GM one was alum and the F*rd sending unit was stainless steel so welding them together wasn't an option.

From there all I did was make sure the float arm would move roughly in the same position and the F*rd one, marked and drilled 2 holes and bolted the GM potentiometer to the pick-up tube.

The wire arm on the GM float was too long to match the original range of motion of the F*rd one so I cut it down close to what it needed to be and bent it to fit back into the arm. All I had to do from there was tweek the position of the float arm to match where the full and empty limits were that I mapped out when I started. Then I soldered the blue sending unit wire back onto the tab of the new potentiometer.

Just to make sure I didn't screw it up and also because my tank was still out of the truck I installed the completed sending unit in the tank and checked it with a multimeter. It was roughly 1-2ohms with the tank sitting empty so I flipped the tank over to simulate full and took another reading and it was 92ohm full, well within any error for a sending unit.

I got a couple PMs asking if this mod would work with a stock set of gauges so I looked at my original 0-30ohm sending unit from my fuel tank that was behind the seat and it will work almost identical to how i listed above. the only difference that I noticed was that since the stock one is steel you would be able to solder it to the mustang backing plate or mig weld it on if your mustang unit wasn't stainless like mine.

Hope this helps

[55metalmonkey]

After everything was done it was all hooked up, looks fairly clean and almost like it belongs there

[OrrieG]

Your detailed sender mod fix is going to help a lot of folks. Plus I always like it when like minds take up the challenge of figuring out how to make it work.

[_Ogre]

Originally Posted by 55metalmonkey

... why anyone in their right mind would put anything f*rd in an old Chev/GMC...

truk has mustII ifs, ford fusion seats, chrysler new yorker trunk lid, 03 mustang trunk hinges, latches, hydroboost, master cylinder and rear view mirror, nissan quest remote mc reservoir and probably a few things i missed. i'm over your infraction already

nice write up on your dilemma. you'd thing some electrical engineer would come up with a couple of diodes and resistors to fix an ohm to ohm problem. i've looked for a 30 ohm to 90 ohm solution, no easy fix.

have you figured out how your going to bolt your bed strips down?

[55metalmonkey]

I thought about that and since not not much of my truck is stock anymore I was going to either make my own wood strips (mahogany) with polished alum runners and use stainless steel machine screws through the alum runners and into threaded inserts into the cross members
or
do a full bed in marine plywood and cover the whole thing with some fancy veneer work (marquetry) and secure around the perimeter with hidden T bolts

[55metalmonkey]

[QUOTE=_Ogre;6346268]truk has mustII ifs, ford fusion seats, chrysler new yorker trunk lid, 03 mustang trunk hinges, latches, hydroboost, master cylinder and rear view mirror, nissan quest remote mc reservoir and probably a few things i missed. i'm over your infraction already

Me too, I go with what works.... although I have mostly Camaro, El camino, Silverado stuff in mine but there is a few F*rd parts and even a couple Hyundi hood hinges I modified for my fiberglass touneu cover

[Vova]

What did you do for the filler?

[Vova]

Who has the best price on the tank and sending unit?
Thanks...

[mr48chev]

Vova I think you just have to hunt a bit to find the good price on a quality tank. All of the Mustang goodie vendors have them, you can find them on Ebay. Locally I can walk into the O'Reilly's and order one for 164.99 plus Tax and that might trump the "internet deal" and shipping and handling.
If you or someone in your household has Amazon prime put 1967 Mustang Gas tank in the search and they have a number of options with somewhat friendly prices. My link didn't work.

The lowest I found http://www.carparts.com/details/Ford...FUOVfgodOxYAtA But they don't say what shipping is going to be.

As far as 16 or 18 or more Gallons, my back and bladder won't outlast the miles I can go on 16 gallons so that is somewhat of a moot point. More capacity is nice on the long hauls across the western states though as it does give you that extra bit of reserve when there are areas where gas stations are 100 miles apart.

Right now I have a 20 gallon aluminum tank in the truck but it hangs down a bit further than I like and the Mustang tank would get me more clearance on the back of the truck.

55Metalmonkey Thanks for taking the time to put that together and post it. It is one of those things we run up against all the time that has a simple solution but we tend to make it be a hard one. I've got the thread subscribed to and bookmarked both for future reference.

[Vova]

$151 for tank and sending unit from Amazon. Thanks for the advise. Should have it by the weekend...
Do I need a in tank fuel pump or will my stock pump pull fuel from a rear mounted tank?

[DransportGarage]

16 gal tank w/ sender and hose at Kentucky Mustang - $133.95, free shipping to Los Angeles. (I checked shipping to L.A. and Ohio and they were both free.)

http://www.kentuckymustang.com/product_p/5296.htm

[Vova]

Originally Posted by DransportGarage

16 gal tank w/ sender and hose at Kentucky Mustang - $133.95, free shipping to Los Angeles. (I checked shipping to L.A. and Ohio and they were both free.)

http://www.kentuckymustang.com/product_p/5296.htm

Good find!

[lowrodderchev]

That's were I got mine from I'm happy drilled the top for Chevy sender no more guessing

[Aaronoregon]

Or just go with a programmable Dakota Digital gauge for anything you use........

[55metalmonkey]

Originally Posted by Vova

What did you do for the filler?

I used an in bed filler neck, I don't have a pic but it's probably the most common one used on these 55-59 trucks.

[55metalmonkey]

Originally Posted by mr48chev

55Metalmonkey Thanks for taking the time to put that together and post it. It is one of those things we run up against all the time that has a simple solution but we tend to make it be a hard one. I've got the thread subscribed to and bookmarked both for future reference.

Thanks

Originally Posted by Aaronoregon

Or just go with a programmable Dakota Digital gauge for anything you use........

True that this is an option but for those trying to maintain their original guages and also want to relocate the tank I think swaping out the guage sending unit seems a little more cost effective

[Vova]

Does this tank need a vent? I think my in cab tank has one.

[G&R's57GMC]

Originally Posted by Vova

Does this tank need a vent? I think my in cab tank has one.

The Mustangs used a vented cap.

If you mounted the tank in the C of the frame instead of on top of the frame you would have room for a filler neck that you could add a vent line to and route the vent line over to the stake pocket and make a u turn up in the pocket, then use a sealed gas cap.

[Vova]

Originally Posted by G&R's57GMC

The Mustangs used a vented cap.

If you mounted the tank in the C of the frame instead of on top of the frame you would have room for a filler neck that you could add a vent line to and route the vent line over to the stake pocket and make a u turn up in the pocket, then use a sealed gas cap.

I'm mounting my tank on the top of the frame with the filler neck in the bed floor.

[Vova]

Should I add a vent to the tank? I could drill one in the the sending unit.

[mr48chev]

Originally Posted by Vova

Should I add a vent to the tank? I could drill one in the the sending unit.

I've seen some guys do something similar and put a fitting on it to run a hose over and up into the stake pocket so the vent is several inches higher than the top of the tank. I' d stick some sort of filter on it if I did that to keep from sucking dust in.

[Dan in Pasadena]

Originally Posted by mr48chev

?.. I' d stick some sort of filter on it if I did that to keep from sucking dust in.

How about just running the hose up the stake pocket long enough that at the end you turn it back DOWN again a couple inches - no dust! (Well, not much anyway)

[Vova]

Maybe something like this.
http://www.attwoodmarine.com/store/p...tic-deck-fills

[whitedog76]

Universal sending unit.

http://www.tanksinc.com/index.cfm/pa...rod/prd276.htm