Playing the "get the right combo" game on the gauge.
Had an accident (nothing serious, just pushed down on the dash where I shouldn't have) and mechanically broke my gauge.
Tractor is the 4 cyl 1963 2000D with the "lock ring" type sending unit....has the 6 holes in the disc but smaller diameter and thinner material than the regular 6 screw mounting type. Went to the parts section herein and found the two different sending units so moving on from that:
My sending unit has the older black plastic float with the exposed resistive element. The PO had the float arm adjusted to it's shortest length. This made the float submerge. In looking at the pictures of both types I see that the float arm is fully extended for max "inch-oz" of flotation leverage. So I put it back like it seems to have been originally, fully extended. I don't know if it's fuel logged or not....TBD.
The tank, as you know, has the dimple along the top to fit inside the cowling. My current fuel level is just below the point where the tank top starts to form at the edge, being 1-2" below the opening. At that point I measure around 65-70 ohms. I bought a replacement gauge that is supposed to be for this tractor, didn't specify which sending unit and this fuel level reads a little less than ¼ full.
The printing on the dial of my replacement is different from the OEM and the gauges pictured in the parts list herein which has the tank level marked with fractions at 5 levels. Also, unlike my original gauge which only uses 2 terminals, one to the tank and the other to 12v, my replacement uses 3 with one going to ground.
I have operated the sending unit through it's full range and it runs from over 180 ohms at empty to around 10-20 at the full up position...depending on where you stop lifting. Using a resistor to simulate the sending unit, 20 ohms makes my replacement gauge show full even though 70 ohms puts it at ¼ when installed as listed above.
Since there are 2 different sending units listed for the types of mounts I am concerned that only one 12v gauge is offered to be operated with both types of SUs. If they were the same, my existing replacement gauge would work.
So, with all that said, I don't know which way to turn. With my current replacement gauge, I either need a sending unit that is of around 10-
20 ohms at my current fuel level, or a gauge which has less internal resistance so that more current will flow with my 70 ohm sending unit value so that the needle will move on over to the F mark area.
Shunting the sending unit with a resistor to lower the F resistance is not the answer as empty is basically open circuit for the meter and the shunt resistor, being a low value, will force the needle to indicate more fuel than is in the tank at other than F levels.
Hope this isn't confusing.
Thanks for your time,