OHM range on a '38 Plymouth fuel tank sending unit

[Tim B]

The factory service manual was of no help to me on this one.  (or, I should say the reprint that includes the '36-'42 Model years).  The '38 I have uses a one-wire sending unit, which the wiring diagram in the manual confirms.  The manual showed a gauge illustration that was nothing like the unit in my dash.  This is on a 55,000 mile car, certainly with original equipment in the dash.  The malfunctioning sending unit was a replacement that was built by one of the vendors that the owner of the car used some time back.  The owner mentioned that at the time he had the sending unit built, he was asked if it was a 2 wire or 1 wire unit, so there must be some differences.  Maybe P5 or P6?

[Lew]

Can the dash guage for the '36 -42 models be calibrated as stated in the factory Plymouth service manual? The Motors service Manual for the same years appears to state that the dash guage,( Motometer Neco) is not adjustable for the full and empty settings. Will bending the float arm help to some degree?

[Go Fleiter]

Tim, I had the same "dead spot" too, which seemed to be that part of the sending coil, which was used / consumed most. I carefully (without destroying the fine wire connection) turned the coil 2 or 3 dergrees and got it. I got a somewhat uncorrect reading because the Ohms relative to the arm movement changed a bit. Maybe You can get the same by bending the arm?s contact a bit out of its old way, carved into the coil.
Greetings! Go

[Tim B]

I made an attempt to use the search feature prior to making my post, but perhaps used a query that didn't yield the result that you provided, Go.

According to our meter, our sending unit appears to have a "dead spot" through it's range, resulting in a gauge that tends to bounce around as the car is traveling along.

Thanks for your insight, Tod.

[TodFitch]

Does anyone have the OHM range on a '38 Plymouth P6 fuel tank sending unit?? I couldn't find it in the shop manual.

The 1936-49 Plymouths used a two-wire sending unit for which I have never seen resistance specifications published. You can get replacement sending units from the usual old Plymouth part suppliers. I suspect that they get theirs from Atwater-Kent but don't really know.

Regarding your system, the usual issue is a bad ground or bad wires: Both wires from the dash unit to the sending unit must have equal and low resistance and both the dash unit and the sending unit must have good grounds.

For 1930-35 single wire sending units I believe the empty reading is about 120 Ohms while full is about 8 Ohms. However my attempts to match a modern unit to my dash unit have been unsatisfactory: I can make the gauge read correctly at full and empty by the modifying a modern universal unit but result is unsatisfactory (3/4 tank reads about 1/8 tank, etc.).

[Go Fleiter]

see: 35 gas tank and sending unit...

http://plymouthbulletin.com/smf/index.php?topic=1894.0

Maybe You find a couple of hints. there.

(btw. we have a search funktion in this forum)

Greetings! go

[Tim B]

Does anyone have the OHM range on a '38 Plymouth P6 fuel tank sending unit?  I couldn't find it in the shop manual.