calibrate fuel gauge on P15?

[Sam Buchanan]

The fuel gauge on my '48 is working but indicates a 1/4 tank too high. I confirmed this by removing the sender, hooking it back up with a ground wire and moving the float all the way to the "empty" position. The gauge indicated 1/4 tank. I studied the diagram of the gauge in the service manual and found a couple of "calibrating arms"  but am very reluctant to open up the gauge unless somebody has foolproof data about how to tweak the gauge (and have it still work!).

 

Any ideas.....other than the little piece of masking tape stuck to the dash with the mileage last time I topped off?    Yes, I could buy another sender but hate to do that if the gauge is out of calibration.

Edited June 17, 2019 by Sam Buchanan

[Plymouthy Adams]

is the float mechanically against the stop or is the float against the tank bottom...? and how many ohms are on terminal 1 and how many on terminal 2...?

Edited June 17, 2019 by Plymouthy Adams

[Sam Buchanan]

Indicates 1/4 tank when the float arm is down on the stop (the sender is out of the tank). I stuck a ruler in the tank and the depth of the tank and the drop of the float when all the way down was about the same.

Edited June 18, 2019 by Sam Buchanan

[Plymouthy Adams]

that is answer to part one.....electrically, where are you at?

[Sam Buchanan]

I didn't check the resistance of the sender, guess I could do that to see if the sender is still in spec. What should the range be, saw that somewhere but forgot. Is it 10-73 ohm?

Edited June 18, 2019 by Sam Buchanan

[Plymouthy Adams]

on the 48, you should be a two wire setup....the second series (p15 carry over into 1949) could have the single wire....which one do you have....?

[Sam Buchanan]

1 hour ago, Plymouthy Adams said:

on the 48, you should be a two wire setup....the second series (p15 carry over into 1949) could have the single wire....which one do you have....?

 

Mine is the two-wire sender, I have a very early '48.

[Plymouthy Adams]

if a two wire you will have only 28-32 ohms across the two terminals of the sender...AND this is divided by the wiper (ground) to post 1 and 2......if you have 10 ohms on 1 you will have 20 ohms on 2   This action needs to be smooth and linear as it divides the resistance....this gauge is designed to pull the needle in both directions at the same time..

[Sam Buchanan]

17 hours ago, Plymouthy Adams said:

if a two wire you will have only 28-32 ohms across the two terminals of the sender...AND this is divided by the wiper (ground) to post 1 and 2......if you have 10 ohms on 1 you will have 20 ohms on 2   This action needs to be smooth and linear as it divides the resistance....this gauge is designed to pull the needle in both directions at the same time..

 

I think the mystery has been solved. One terminal to ground is 18 ohms, the other is completely open, and terminal to terminal is open. Looks like the resistor has a broken connection at one terminal. I'm thinkin' that would explain why the gauge is being driven to one extreme of it's travel since only one bimetal arm is getting heated. Guess a new sender needs to be added to the wish list.....

Edited June 18, 2019 by Sam Buchanan

[Sam Buchanan]

Follow-up; problem solved with new sender.

 

Note; As of this writing, the price shown in the Kanter catalog is for the one-wire sender, the two-wire is considerably more ($97).  However, Kanter send a replacement sender for the one-wire version that was sent in error.

Edited July 5, 2019 by Sam Buchanan