QuestionI've been the custodian for this old girl for about 7 years now and I think its time to address the fuel gage that always jumps to "full". I'm not a mechanic by trade so please assume I know nothing. Is it the gage or the sending unit?
AnswerIt could be either one, or there are other possibilities (wiring, for example).
So, let's start sorting them out.
First, inspect the wire at the back of the car that goes to the sending unit in the tank, at first looking at it WITHOUT disturbing it. Is it the original, cloth covered wire? If so, there is a very good chance that somewhere along it's 20 foot length, the insulation has cracked and fallen off, leaving the copper strands inside the wire free to come in contact with bare metal. If that happens, it will immediately peg the gauge as soon as you turn the key on.
If that wire has been replaced with modern wire, that is not likely.
Second: If you don't see any obvious problem with the wire, disconnect it from the sending unit in the top of the tank, and let it wave free in the air. Now, turn the key on and see what the gauge does.
There are two likely results:
1. Same result? The problem is forward of the tank unit - but we still don't know everything. It is still possible that the wire is bad, or there is a problem with the dash unit.
OR:
2. The dash gauge now does not move when you turn the key on. Good - we have tracked down most of the problem - the sending unit is shorted to ground - probably the sending unit itself has failed. Remove it and inspect it - does the arm swing up and down freely? Do you feel a minuscule rubbing sensation in the unit as you move the arm, or does it appear to have no internal activity at all? If you are brave, you can gently bend back the tabs on the enclosure and inspect the rheostat winding inside the sender - perhaps you can see what is wrong visually. Typically, the windings have come loose and are touching the metal enclosure. You can admire the ingenuity of the design, but unless you are a very skilled craftsman, you are going to have to send it to a specialist to have it repaired. Such folks advertise in Hemmings Motor News and other places. Or else you can call my friend Stuart Blond at Kanter Brothers Packard Parts in New Jersey and order yourself out a replacement sender. There are other Packard Parts Vendors also - you can find them with a Google search.
Replacing the sender with a good one may or may not finally solve the problem - because having been shorted for a long time may have damaged the dash indicator unit. If you want to be sure about things, replace it also - or take a chance and just do the sender first.
Back to the wiring inspection: There is really no way to track down bad wiring problems if the harness is original. My advice in that case is to buy a complete replacement wiring harness for the car and install it - the car is a time bomb waiting to go off with the original harness in it! Modern replacement harnesses are available for your car, made from safe materials - check in Hemmings for that, or go online and Google "antique car wiring harnesses". I have had very good results with Y and Z's Yesterdays in San Bernardino, CA, but there are many others.
Back to the #1 result above: To investigate the dash unit, identify the wires on the back of the gauge. Figure out which is the one that comes from the sending unit by comparing the color coding of the wire that you saw at the tank unit, or by noting where the wire goes physically. Disconnect that wire at the gauge, and now turn on the key - if the gauge still pegs, it is bad. If the gauge is now inert, the wire to the back of the car is probably the culprit.
Finally, and just in case you are not aware of this, there is a feature of this car that helps you to tolerate an inoperative gas gauge: Remember that when you fill the tank, you hear a whistle coming from the filler pipe. This whistle only sounds when the fuel level is between about 5 gallons at the low end, and 1 gallon short of full. You can use this to check your fuel level any time, by taking the gas cap off, and nudging the car body sideways so as to get the gas sloshing in the tank. If you hear the whistle chortling away in there, you know you have a least 5 gallons in the tank. If you don't hear it, the tank is either brim full, or has less than 5 gallons; you can probably figure out which by asking if some angel has kindly filled your tank for you. If you don't think so, you'd better head for the gas station.
Dick (still driving his 47 Packard, with the same feature)
