The Stovebolt Site Forums The Shop Area General Truck Talk 1952 Chevy Truck behind the seat fuel tank

Was looking at my fuel tank behind the seat. It appears to be sitting at a slight angle instead of straight up and down on its side. I have my 0 - 30 ohm reading with the fuel sender out of the tank and it is showing a correct reading on the fuel gauge as well, ground wire is clean and solid. When I re installed the sender unit into the tank reading is not correct. Would the tank not sitting perfectly straight cause this kind of a problem? Thanks Hugh

Not sure what you mean by not straight up and down. If you mean that tank appears to be leaning back , that is because the cross section of the tank is not rectangular - it narrows towards the top. See image.
Is it a new sending unit? They are adjustable.

Hugh, the below pic snagged from an earlier post in another thread by fellow Bolter Otto Skorzeny shows the installed orientation of the tank you mentioned and described by Waveski above.

Perhaps you could provide more details on the sending unit in question. Was it previously installed and accurate, or is this a new sender that you tested outside the tank before installing for the first time??? Is it possible the range of motion of the sender arm out side the tank is greater than inside the tank? I think you would need to double check that to be sure the arm has the same swing and isn't rubbing against the inside of the tank.

More details and perhaps a pic or two would help ID what may be going on.

If the gauge system works correctly when the sending unit is out of the tank, but reads very low to empty when installed check for a sunk float.

The float is usually offset; the sending unit has to be oriented is such a way that it doesn’t hit the tank wall.

At this point we are throwing darts with one eye closed and the other one squinted. More information is needed.

Yes the tank has a lean to it, the top of the tank leans towards the rear of the cab. Thinking the top of the tank where the sending unit is, should be flat as possible to ensure sending unit sits straight in the tank for max accuracy. I check float to make sure it did not have a hole in it as it is real super light instead of heavy. This the third sending unit have had this problem with all 3. It was mentioned that the unit is adjustable, is this by means of bending one way or another? works fine out of tank, just not in the tank.

The sending unit is adjustment is determined by the point of attachment of the float assembly to the fixed vertical frame.
The units I’m familiar require that the fasteners are loosened and the float assembly slid all the way to the bottom in order to wiggle the unit into the tank, then the whole thing is lifted partially up and tightened together at the proper adjustment point.

I hope that made sense the way I worded it. I learned through trial and error.

Here’s what my sender looks like.
The attachment of the float assembly is all the way down in the picture. That’s the way it needs to be to get it into the tank. After it’s in the tank you need to slide the float assembly part way up on the fixed vertical frame to achieve the proper adjustment. If left at the bottom as shown the float would lay on the bottom of the empty tank while the gauge would falsely indicate that there is fuel remaining.

Before you put the sending unit into the tank you can preset that adjustment point while holding unit up against the outside of the tank , then marking the vertical frame with a sharpie.

In what way does your sending unit malfunction when installed?

It show 0 to 30 ohms, empty to full, manually by picking up the float assy and moving it from the down posit to the up posit and registers empty to full on the gas guage when it is out of the tank. Once I insert it into the tank it does not show the correct gas tank fuel level. How do u adjust the 0 to 30 ohms to match the actual fuel level in the tank?

I think my 54 has a ground wire from one of the top screws on the sender to the brace behind.I am not electric wizard so check to see if this is correct for your truck .

Definitely check the ground wire. My '51 has one that leads forward (don't know exactly where it went, but I plan on landing it somewhere forward on the firewall (maybe under a screw for the brake switch or dimmer switch.) A bad ground adds resistance to the circuit and can affect what the gas gauge indicates for level, throwing it off. Also check if your cab (or wherever the ground wire lands) has a good ground path back to the battery.

Yes, it's hard to tell in that photo but the ground and gauge wire are both wrapped in the same woven insulation. Ground is attached to one of the attachment screws.

For what it’s worth, mine has a single lead. Center post on the unit, wired down to the sender.

Was checking out your pic of your gas tank, i have the same setup, ground to cab brace, will recheck my ground to be safe. Notice in ur pic your tank seems centered, creating a good flat surface so the sender. My tank is angled top towards the back of the cab and when u think about it that sender is also at an angle instead of straight.

That begs the question- why is your tank at that attitude?

How about some pictures?

The tank rests in two cradles that allow for some rocking movement from front to back. It's just held in place with two flat spring steel straps that are cinched down tight. Loosen those up and orient your tank to the proper straight up and down position and then cinch them up tight.

The tank sits on pads made of roofing felt or some such. If it's disintegrated, the tank may have loosened up and moved.

I used peel and stick flat roofing material in place of the felt when I put in the new tank.

I would think that for the tank to be leaning back , the lower front would have to move forward.
In my truck there is barely 1/4” clearance between the front face of the tank and the flange of the seat frame.

Or–-
Maybe the OP needs to place a soft interface between the back of the tank and the cab wall stiffeners to bring the top forward. (I did that.)

Pictures sure would help.

Have you confirmed the ground wire is good with a ohm meter?

Have you tested the sending unit with a long temporary ground jumper wire going from the battery negative terminal to the mounting screw on the sending unit?

Mike B

I bought my 52 about 12 years ago, not sure how many owners or hands this truck has been through in its time. When I rest a bubble level on the sender it is off center. Seems like a good idea to have this area level and straight. My son will have to help me with pics and he is not here right now.

If the tank is off'-level by say 10 degrees (which would be very noticeable) the change in float travel versus gas depth would be about 2%. NOT noticeable. Unless it might have caused the float arm to bind up, which is unlikely. A bad ground would be more likely than the tank position causing an issue.

Will loosen strap and try to straighten the tank in the morning, I have 0 - 30 ohms from the sender to the gas gauge manually with sender out of tank, in the tank on its own the gas level is off about one quarter to almost a half tank. will run a jumper off the neg battery term to the sender ground screw in the morning, will get back to yaw in the morning, runnin out of light and the skeeters are getting hungry.

What about the float adjustment factor?
You haven’t commented on that since asking if that is accomplished by bending , which it isn’t.

Again- the float assembly has to be slid all the way to the bottom of the vertical frame to get the sending unit into the tank. If it is left in that position - as in not adjusted - it will send erroneous information.

I don't have a dog in this fight---just showed up now and reading this thread-- but how do you readjust the float assembly after it is in the tank?

Here’s how:
Hold the sending unit outside the tank.
Slide the float assembly up/down on the vertical frame to the position in which it looks like the float will be at the bottom of the tank when there is no gas to float it ( empty tank).
Mark that position on the vertical frame.
Slide float assembly all the way down- that’s the only way to get it into the tank- then wiggly the sending unit into the tank.
Lift the unit, slide float assembly to the adjustment mark and fasten it there.
Lower sending unit into working position and fasten to tank.

Waveski, is your adjustable arm sending unit the one from ebay recommended and tested by Jon G?

It’s been a couple years, but I think it came with my wiring harness.

With my sending unit, if the float arm attachment is left at the bottom of the vertical frame, the float would bottom out in the tank and show fuel remaining when the tank is empty. That’s why I described my adjustment procedure; it needs to be set at a functional elevation after the whole unit is wrangled through the opening in the top of the tank.

It’s too late for pictures of that because my tank and sending unit installation is finished.

I will note again, for interest , that I’ve never had a ground wire for that sending unit. It must have been grounded through the tank in contact with the cab. In the course of installing my new tank. (Thanks, Spectra) I incorporated cushion material at all the hard points. I suspect I will be adding a ground wire.

What unit are you referencing, as recommended by Jon G?

Mine looks like this one–-

Mine was the same as yours. My first sending unit worked fine outside the tank and no go when installed. After many times removing and installing, bought a new same style sending unit and it worked. Problem with the first was the the hot wire would lose continuity when installed to the center stud. I did run another ground to the cab brace, oringinal still in use also, can't have to many grounds. To correct my full to empty measurements, I bent the float arm a little. Not perfect, shows full, but still have several gallons left when empty. I like it that way.

Years ago...maybe 2 or 3 when I was working on the fuel sender project I posted the chart/formula for determining the proper length of your post (dependent on the depth of your fuel tank) and the length of your float arm. In the AD you have about 11 to 11.5 inches from the top of the tank to the ledge inside that works sort of like a slosh preventer but actually only stops travel of your float so you still have a bit of gas when your gauge reads Empty. The best sending unit I've found is one sold by an eBay seller whose ID is renbusan. It was designed in Taiwan and whoever did the work got it all correct. Attached to this message is a drawing I made of how the AD OEM and any replacement gauges should be adjusted. Here is the important point: if they aren't set up like this, the sending unit won't send the right reading (in ohms) back to the gauge. The OEM sender post sat at an angle. Replacement posts are straight vertical. Cut/trim the vertical post of your replacement sending unit so that the pivot point is half the distance from the top of the tank to the bottom (5.5"). Unless you are working on an OEM unit (doubtful but possible), trim and bend the swing rod so that from the pivot point to the center of the float is 5 7/8". Then your float assembly will follow what I call "the gas tank sender formula" and all will be Jake for you. Good luck! Also...important point...most of the replacement sending units are made so the float can snap on to the rod pointing in or out. Your sending unit can only be installed one way...the screw holes cause this to be so. Please make certain your float points to the inside of your tank. Otherwise it could/probably will rub against the wall of your gas tank. I have received questions about this project and I still receive them. The bottom line is this: I can make a precision fuel sender that will last until around a month after forever but I can't do it for $30. That's what the unit from Taiwan will cost you, shipping included.