Stock fuel gauge/modern sending unit

[bobj49f2]

Craig,

Thanks for your input. When I talked to you on Saturday I was going down the freeway so I couldn't really concentrate on our discussion but I got the gest of it. I looked at a stock sending unit yesterday and tried to take a reading off of it but but got some wierd readings in the "full" position, I think it might be junk or you just can't accurately test it that. Like Mertz stated, the shop manual isn't much help. I'll play around with it tonight and see what I get. I just wanted to make sure I wouldn't wreck anything or blow anything up buy doing what I was proposing but from what has been posted it looks like no one really has the absolute answer so it's time to experiment. I just have messing with gas, I agree with Craig with the question of inserting an electrical device in a tank of gas. We all know how dangerous the stuff it is.

[bobj49f2]

OK, after talking to a friend/customer, who is an electrical engineer I think I have a solution to my stock gauge/new sending unit puzzle. I thought maybe someone would be interested if they happen run into the same problem.

I installed a combination of resistors and a potentiometer in line between the sending unit and the gauge to limit the voltage going from the gauge to ground, this prevents the gauge from pegging out to "FULL". Second, I installed a set of resistors and a potentiometer across the studs on the back of the gauge to adjust the span of the travel of the needle. The gauge had a resistance of 10 ohms. Tonight I was able to get the sending unit and gauge to register correctly, at least somewhat accurately. Probably just as accurate as the stock set up would. I used the potentiometers to tweak the values a little at a time. Now I have to disconnect the whole set up and measure the potential of both combinations of resistors and potentiometers to find out what size resistor I need to replace both cobbled together resistor packs.

[cmoritz]

Hey Bob,
I've been thinking about this the past few days, maybe I missed something..Your trying to retro-fit the IH Tank and sender right?
Why not just swap the gauge to the newer style? Or, why not modify the new tank, and install the old-style sender...but use one from say a 53-55..then tweak and play with that.
The question still remains on the fuel compatability..though I think it would be negligable, of gasoline vs diesel.
Also , while not a difinative answer to the "spark-in-fuel-tank" question, I did notice a diaphragm separating the float and bi-metal contact pulse-sender. I would think this acts as a vapor seal, isolating the vapor from the spark. Dmptrkr pointed this out , as well as the modern fuel gauge option.. I'm begining to wonder with that handfull of voltage regulators and resistors you have , ..if your not venturing into the forbbiden
"Darkside.."..clearly , with those modern parts and electronic therories, you are straddling the fence...careful!..it's dark in here!

[imlowr2]

potentiometer? What the heck is that? LOL... Sounds like you have the problem solved, but if you know the ohms required on your guage, it should be possible to find a sending unit with the same range of ohms. You should be able to eliminate the resisters. I would think the guage you have is standard. Makes me wonder how accurate these digital guages are? They must be really sensitive to reading the sending units. Great info Bob...

[55 dude]

one of the slickest ways i have seen to solve this problem was the use of newer gauge with old gauge face, it works beautiful and is still working smooth. when you purchase repro gauges that is what your getting,new combined with old.

[bobj49f2]

I keep all my trucks as stock as possble, including the 6 volt system.

I want to keep the stock gauge. The problem with the newer tank is I modified it quite a bit to fit under the truck. I relocated the fill tube to fit the stock location, I also had to relocate the sending unit. I had to turn the tank 90° to make it fit. At the time I didn't realize the sending unit would cause a problem, I just thought the sending unit would send out a 0 to whatever ohm signal, a pretty standard signal. I didn't start to really think about it much until I talked to Dmptrkr one night, he told me he thought the systems were different. When I relocated the sending unit I made a new mounting collar to fit the newer sending unit, which has a small hole than the older, stock one. I don't want to have to pull the tank, drain it of gas, fill it with water (I don't want to blow myself up) cut out the collar, cut a bigger hole, weld in a new, wider collar, rinse the tank of water, reinstall. I think adding a couple of resistors is a lot less, dangerous work. When I got the tank it had diesel fumes but I flushed it out and went to work on it, I don't like working with sparks around anything with gasoline fumes.

BTW, although I like to keep my trucks as close to stock as possible I do make modifications when neccesary. I have a pickup chassis under my panel and I needed a panel truck gas tank, the one in the original chassis was completely rotted out so I had to use the closest tank I could find. It only cost me $75, including shipping when I bought it.

[55 dude]

the mid 60's+ fords are 6 volt, they have a voltage drop on them. with this gauge mod. you can't tell its not stock at all,really a pretty slick update. napa sells a adjustable ohm sending unit that might work. not a personal recomendation as i have never used one and hate wasting money on bad info.

[bobj49f2]

I invested $5 in a few resistors today, actually I bought a variety so I can play around with them. If they don't work I'll have to check out the NAPA unit. That's for the tip, I didn't realize someone made adjustableunits.

[bobj49f2]

I got it all installed tonight. I used a 33 ohm resistor to shunt between the two posts on the gauge and I got a 1/2 ohm resistor in between the sending unit and gauge. It seems to be fairly accurate, probably about as accurate as the stock set up in my F-2. At least I now know about how much gas I have. I just have to make sure I keep it above a 1/4 tank. I know there is a little reserve after it registers empty because there's more than an inch below the float when it's in the empty position.

[gdgerland]

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