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Alright all you AD truckers...I need help! I have a new, correct tank for my '48. I bought a sending unit from Classic that they say fits a 47-53.
Hold on now, a 47-48 is a different tank than the 49-53, but Classic says it will work.
And it does, but...I do not get a symmetrical reading across the gage. The stock gas gage has E, a little dot, 1/2, a little dot and F. Do the little dots represent 1/4 tank marks? If so...
While the gage read a little above the 1/4 mark, I drained the tank (it has a plug in the bottom for all you gas thieves out there), and got a little more than an empty 5 gallon jug could hold. That would be somewhat near correct for where the gage read.
I turned on the ignition and read the gage, now at completely dry. It came up to the first little dot on the gage. Then I put 4 gallons in...did not change the gage at all.
Ok..I am kind of a smart guy (I thought) Took it to a nearby gas station.
Added 4 more gallons in it, stopped, (should be at 1/2 tank ) turn the ign back on...same little dot.
4 more gal in, (now 12 total) same dot
3 1/2 more in (completely full at the fill neck) read almost half on the gage.
Started it up and drove home and it gradually came up up to a little above the 3/4 full dot. Now I am wondering if the dots are empty and full!
Do I need to plan on carrying a 2 gallon jug of gas with me at all times?
I still can get this thought that the sender is wrong out of my head!

no the dots are not E & F - the sender for "47-53" is an aftermarket universal style, not as original, you might be able to adjust it somewhat by bending the float arm to suit your gauge .... sounds like the float isn't dropping as far as needed - with the tank either full or empty bend the arm a bit up or down until it reads right .... empty should be about E and full should be about F

with any new setup the best plan is to fill it and see where it reads, carry some gas with you and watch mileage compared to the reading until it runs out and see where that reads .... should be able to get 150 miles min on a tankful, so about 75 miles should show about 1/2 .... the important thing of course is to get it so the gauge reads close to E when you run out

Bill

That universal sender needs to be customized, if you haven't done so already. You need to adjust it so it is shorter and your float arm is at the precise length. Their specs are down to the 1/8 or 1/16 of an inch if I remember correctly.

Secondly, make sure you have a ground from the top of the sender (outside of tank) going directly to the neg on the battery. I found this to make sure the ground is proper.

Or you could have a faulty gauge, but I suspect ground and float rod length and height

Thanks guys. I did make very sure of the ground when I installed the new tank. But I did not check for accuracy before filling or modify it in any way. Guess i will run the now full tank down and pull it out to check sender. It could also still be the gauge.

I am having pretty much the same problem, the sending unit I bought said 6 or 12 volt, 0-30 ohms. The sending unit was universal and it came with a chart. The tank behind my seat in my 53, 3100 is 12 inches high. The chart shows where to adjust the up and down arm travel at 6 1/8 inches and the length of the float arm 7 9/16 inches. If I lay the sending unit on the bench and measure the tavel from top to bottom of the float at this adjustment it gives me 11 inches travel. I figure about right for a 12 inch tank. I think I did that part right. Just for the hell of it I put my ohm meter on it and put the positive lead on the sending unit wire screw. I touched the negative lead to the top of the sending unit one of the screw holes that go into the gas tank. The ohm meter goes up and reads, to me that is counter intituive. Doesn't the center screw that is insulated from the rest of the sending unit and the wire running down to the reastat sound like it is grounded? Shouldn't I have gotten no reading at all? Is it shorted out? This is the second sending unit I bought and I think my thinking is backwards. Does Denny still stop in to read these boards everyonce in a while? He has slapped me around before and showed me where my thinking was flawed, not that anyone else can't tell me how stupid I am, I am always open to that. OK, well I won't install it quite yet and see if I get an answer from someone that will tell me everything is OK (hopefully). I bought a new sending unit and a new 6 volt gauge. Thanks John

Uh, are not the "sending unit wire screw" and the "center screw that is insulated" one and the same? One wire to the ohmmeter should be hooked to the sender wire screw terminal (on outside side on tank) which by the way is insulated from the mounting plate. The other ohmmeter wire goes to the mounting plate, thus grounded to tank when mounted. When moving the float arm up/down you should see the ohmeter value move. Note...the variable resistor or rheostat is not voltage sensitive. It controls the amount of current flow through the gauge but that is beyond this post and can be quite a can-of-worms. Good luck

Yes, the "sending unit wire screw, and "the center screw that is insulated" is one in the same. I still have it sitting on the bench. Maybe I don't understand the use of the ohm meter but I put the positive lead on the "insulated screw" sticking up from the mounting plate that gets screwed to the top of the tank where I will attach the gas gauge wire. Mind you it is still sitting on the bench, so I put the lead on the screw, then touch anywhere on any part of the sending unit and I am getting a ohm reading. So doesn't that mean the "insulated screw" is NOT insulated and is grounding out with current flowing through the whole thing? Maybe I don't understand the use of an ohm meter but to me it seems like if I screw it to the tank then the "insulated screw" will be grounded also if my bench test is correct? Is my thinking backwards? I don't understand right now. Thanks John

It is working properly. On one end of the sweep it should read 30 ohms. On the other end of the sweep it should read zero ohms, a direct shot to ground.

Thanks Cletis and Beltfed. I will install them both tomorrow.

John, Hold on for a moment. Let make sure you do it right as installing/removing a gas tank is a large pain. Make sure your gas gauge is suppose to see 0-30 ohms (mt to full). Go out and buy a 30ohm resistor at "Radio Shack". Less than 2 bucks at best. OK, take a jumper wire with alligator clips (buy several if necessary). Clip one end of the jumper to the end of the sender wire and the jumpers other end to a clean frame ground on the truck. Turn the key switch on. The gauge needle should come to rest around "E". If it goes to "F" or anywhere else there's a problems. If you read what you want, turn key switch off. Remove alligator clip from frame, clip that end to one end of 30 ohm resistor. Take another jumper wire and clip one end the the other side of the resistor. Clip other end of new jumper to same frame ground. Lay all this on shop towel or something to keep from shorting out. Turn key swich on. Gas gauge needle should move to close to "F". If it doesn't then you have other problems. Let us know what you get and these guys will help. Good luck.

The gas tank is behind the seat, it is a 1953 3100 so I only have to take the seat back off (3 screws into seat frame) and it is all right there, so it only takes 10 minutes, it is no big deal to get access to the sending unit. I installed the new gauge in the dash cluster and the new sending unit in the tank. I hooked up the battery again and nothing when I turned the key on. No movement at all. I used the ohm meter from the tank gas gauge feed wire and the gauge wire on the gas meter at the dash. It is getting a signal so it is not shorted between the tank and gauge under the truck. The old dash gauge I took off came with a paper element that covered the back of the gauge so it wouldn't touch the base of the gauge housing on both sides it had two holes in it so the 2 screw leads didn't touch anything on the cluster housing in the dash. I assume to isolate the signal so it doesn't short out. The new gauge doesn't come with a paper element to isolate it. There is a smear of solder on the back of the gauge between the 2 leads. I assume if I don't use the paper isolation it would short out the gauge. Question? Does the new gauge have different technology that NEEDS it to touch the back of the gauge cluster with that smear of solder? It doesn't seem right then the signal from the sending unit would just ground out if the nuts were tightened and the lead pressed into the cluster housing. This is the second gas sending unit and the second gas gauge. I guess I am doing something fundamentally wrong. Can you help? Can you see what I am saying? When the company I drove tractor trailer for got a brand new truck the first thing they would do was to cut the fuel tank gauge wire. They said if you ever run out of fuel don't bother calling because no one is coming for you, always look into your tank to check your fuel. I guess I could go back to my previous life and look into the tank everytime.

It's better if one tackles just one problem at a time. Work on the gauge first if you wish. I you installed it correctly, applied power, and it's a zero to thirty ohm gauge, and you didn't have the sender wire connected. Yes, something is wrong. If wired correctly with the sender wire off, then it should peg past full. Take all wires off your gauge. Use your ohmmeter on voltage and find which wire is +6 or +12 when switch is turned on. If you can't find voltage on a wire then another problem exist. Most gauges use the mounting screws as ground so that should be good unless you have it dangling under the dash for testing or it has a seperate screw lug for ground. If so, use a jumper wire from gauge case to dash ground. I don't know if your gauge has a wire for dash lights or not. Not to beat this to death but you might call the vender of your gauge and ask them what wire goes where.

If your new gague looks like this
.pic.

Check that it is grounded to the housing.
If you put a fresh coat of paint on the inside of the cluster you will need to clean it off for a good ground
.pic.

.pic.

you do need the paper isolation on the back
.pic.

Good luck

OK DADS50, that explains the whole problem. I put the paper isolation on the inside so the gague wouldn't touch the housing.

Once I sand it and ground it tomorrow it should work fine. Thanks for the pics, they look exactly like mine.

I am glad I asked, thanks all.

Since your going to have the cluster out you may want to take the advice given earlier and bench test it.

I did get the ohm's resister's from radio shack.

Once I fixed the grounding problem I had. I tested it on the bench

1 ohm
10 ohm
20 ohm
30 ohm

Sound like it is a grounding issue. wouldnt hurt to test to make sure there are no other issues.

I will thanks, good idea. Thanks for the pics. Nice truck btw.

Dads50
In your "30 ohms" pic...is this your full level?

My sender is 30ohm.
That will be the full level

I have not installed that cluster yet.

I'm pretty sure that direct to ground reads full and 30 ohms resistance to ground reads empty.

Here is a test I did on the sender I have

Full reading... 33.1 ohm

1/2 reading... 17.6 ohm

empty reading... 2.6 ohm

The sender came from classic parts (chevy duty)
Use this info only as reference, may not apply to equipment you have and my test method may be wrong, feel free to correct