Oh crap...not another fuel sender question

[LBCD]

I know this subject has been beat time and time again, but just maybe someone can chime in as my situation is a little unique

Around 8-9 years ago I changed to 12v and had my cluster in my 41 Tudor overhauled and the fuel gage worked fine with the original tank and sender. Some years after that I decided to put in a new tank and sending unit. I recently got the car back on the road and the fuel gage is reading empty with a full tank. The new sender is a generic type that I cut to size to fit my application probably purchased from Mac' or Sacramento vintage Ford I cannot remember. The bolt pattern for the sending unit on the new tank is a 5 hole application.... so the 6 volt sending unit that I assume I need that C and G carries is a 6 hole application.

The builder who I had rebuild the Cluster has since closed up shop and I am looking for him to answer my question.... But in the mean time I will ask here too.

1. How to tell if the cluster was changed for a 12v system? I'm assuming it hasn't being that it worked fine with the original sending unit that I removed along with the original tank. But you know what assume means

2. If I purchase the new unit (01A-9275) form C and G will I be able to just plug weld the five holes being it has six holes and redrill it making it a five hole application?

I did remove the new sending unit and hooked it up and moved the float to full...it would read full and then drop suddenly without moving the float down. ....then read empty.

Any and all help appreciated! Merry Christmas!

 

[rotorwrench]

Most of the early Fords after the hydrostatic gauge era use a King Seeley type sender that is a current based indicating system. They use a tiny heating coil against a bi-metalic strip to send and indicate. These units are not available new unless you happen upon an NOS part somewhere. If your system was modified, it was likely set up with more modern type resistance based sender & indicator. A person just has to have the correct empty to full ohm value resistance unit in the sender to give the indicator a needle swing to the approximate level in the tank. As the sender ages, the wiper brush and resistor ribbon wear out and eventually there is an open circuit. If your car still has some part of a King Seeley system mixed with something else then you will have a hard time getting accurate indications. I've noted that mixed systems rarely have full accuracy since they are just not compatible with each other. The amount of current it takes one to send will never add up the the amount of resistance the other needs to indicate. There is just too broad a spectrum between the two. You can get close at one end and be off at the other.

For resistance type systems, the different manufacturers have different resistance values for their systems components so you need to know the ohm value of the set up you have to find a part that will work properly if that's what you have.

 

[41LjH]

I think most re-builders use a dropping resistors to drop 12 volts to 6 at the gauges.
The senders vary the ground signal. If you manually move the sender and the gauge reads full and then drops to zero without moving the sender AND you are using the wiring in the car either the sender is intermittent and should be replaced, you have the wiring going to ground, or the gauge is defective. If you look behind the fuel gauge you may see a dropping resistor.
Hope this helps, good luck

 

[rotorwrench]

They will either use a dropping resistor or a constant voltage regulator to lower the 12-volt input to a voltage that will function the system closer to 6 to 7 volts. When it was modified for 12-volt, it is likely something like that is what was added. Going with a modern sender will be problematic unless the indicator gauge is modified for resistance movements. You can take the cap off of the old King Seeley senders and see what it looks like in there. The points might need to be cleaned or there is a loose connection. If it has a constant voltage regulator, it may be on the fritz too.

The new fuel tanks all come with the modern type bung and are not compatible with the King Seeley senders. You just can't win now days with what's available without doing more modifications. A late type sender will only work well with a late type indicator. If a person goes that route, they might as well convert the whole thing to 12-volt function.

 

[LBCD]

Thanks for the info!

I found the builder just now and we talked for a bit. The gauges where set up for 12 v and have the resistor on the back of the cluster as I looked there when I got home from work. He said I need to use the original sender...the ohm reading would be 73-10 ...am I correct? It's very possible I purchased the wrong ohm setting on the new sender. But after reading a number of threads here people are having problems with most of the aftermarket sender's. I need to find one with a 5 hole mount 6v right? He also told me to call the speedo shop and see if they have any info too...thanks for the help!

 

[JSeery]

The original sender will not read 75 to 10 ohms, that is a modern style sender. The original sender (as was pointed out earlier) is a current device that works with points that open and close to control the current. It is effectively a pulse generator, starting and stopping the current as the points open and close. The resistance style is basically a variable resistor.