Packard Forum Index » Pre-War (1899-1942)

Hi all,

The Fuel Gauge stopped working today, it never showed more than 1/2 full, even if the tank is full, I was prepared to live with that as at least empty is empty!

Today it started fluctuate wildly and then died. How does the gauge work? Is it wired to a sender in/on the fuel tank, if so is accessible without removing the tank? Is it a single wire?

How do you remove the gauge from the dash and how do you test it? (I poked around the back of the gauge and it flickered into life for a second)

Thanks guys!

Pat.

If you have an electric fuel gauge then it works pretty simply. The sender on the top of the tank contains a variable resistor coil attached to a float arm. Power is applied to the dash gauge, and the ground wire from the gauge is attached to the sender back at the tank. The ground path travel through that variable resistor and then grounds at the tank body. So basically as the float in the tank moves, it changes the resistance to ground, and that make the needle move on the Fuel gauge.

The most common cause of a gauge not reading correctly or at all is either a bad ground at the tank, or a corroded connection on the wire between the gauge and the sender. Also if the wire gets shorted to ground this can cause the tank to read always empty or full. So clean and retighten all the electrical connections.

The other possibility is that the float in the tank has developed a pin-hole, and the float is full of gas, and has sunk to the bottom of the tank.

If all of those check out then you would have to check the sender to make sure the variable resistor is still in the correct range. If that checks out then the dash gauge is probably bad.

Thank you BigKev!

Can't help with how to remove or much info on 34's but 35-38 6 & 8's used AC gauges. In case they also used them in 34, here is a schematic and general troubleshooting description from an old Motor's manual to go along with Kev's suggestions. The basics are the same but the details are sometimes quite different between mfgs but maybe this will give a start.

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The current problem you have is almost 100% with the sending unit in the tank and not with the dash gauge but check it out as per HH56's info. You need to drop the tank to get the sending unit out, but that's pretty easy too unless it happens to be full with 25 gallons of gas, it's held in place by just a couple of cross-wired bolts - no straps. Typically you either fix the rheostat yourself if your handy, or send it away to one of the many folks who repair these. I don't know if your tank has been cleaned and coated but if not, it's a bit of an issue because of the 3 internal baffles which form 6 individual compartments to prevent sloshing. The individual compartments are connected by small metallic screens at openings in the base of the baffles, and sloshing a coating sealer in the tank often closes them off, leaving you with what might be a 4 gallon gas tank. Most tank rebuilders of these cut the top out of the tank to service the internals.

The earlier problem you had, constantly low readings, was almost certainly because all the years of use had removed the shellac from the cork float. Use of shellac today is questionable as the ethanol in gasoline is a good shellac solvent. There are other coatings you can use to coat the shellac, and some folks just replace the cork float with a brass one from a more modern vehicle. I did mine about 15 years ago and used shellac to coat the cork and it's still OK today despite the modern gasoline.

The 1934 service letters which are on this website have some information about positioning the sending unit float arm. I believe your gas gauge is a Waltham dash unit and S-W sender. It's of the "instant read" type, not the thermostaticly dampened type.

Hi All,

I think I have sorted out the fuel gauge problem.

I dropped the fuel tank, an easy job, but I can't believe 3 bolts hold all that gas in place. Removing the fuel line was not so easy; it must have been installed 'pre-body'., the union was over the tank so I had no choice but to cut it, not much of an issue, I was planning to replace the line anyway. The line from the tank to the pump is steel and showing some light rusting internally. The pipe into the tank from the union is brass.

I removed the sender unit, the cork floats were in poor order and the mechanism seemed to function all right. I wired up the sender to the gauge and moved the cork floats up and down. There was no movement on the gauge.

As the rheostat is riveted together, I drilled out the rivets and separated the two half's. Upon inspection, I saw the contact arm had developed a hole where it runs along the rheostat. It was also paper thin from years of friction.

I cut the damaged end off the arm, bent it and cupped it slightly that it lightly rubs on the inner rheostat ring. Before reassembly, I tested it and it seemed to be working fine, even up to the full mark.

The only question now is the floats, I have polyurethane varnished 2 Champagne corks, and I presume these will do the trick there.

Pat.

Your findings are as expected. I would test it before I reinstalled the sending unit to insure that the two champagne corks have enough bouyancy to lift the arm. Just dip it into a pan of gasoline. If not, buy some cork for the floats, or adapt a brass float as suggested above.

Further....

The tank bung (to drain the tank) was subjected to some hacking by a past owner, so it was unmovable. I drained the tank with an eletric fuel pump.

The short lenght of hose from the filler to the tank was easy to move to one side, the lenght of the inlet to the tank is surprizingly small, it will need carefull attention to ensure a leak proof seal.

I used a camera (similar to a rectal probe one), to look inside the tank, It is in surprisingly good condition, no sign of rust. I also saw the mesh at the bottom of the baffles.

Thanks all for your help!

Pat.

Glad the tank interior looks good, it's a rear issue to fix them. As to the short piece of hose on the filler neck, this tells you it's been apart before because the original was a flexible brass bellows soldered to the tank neck and then to the filler pipe in the tail light housing.

My drain plug was also frozen, while I had the tank down I drilled it out and replaced the original (galvanized?) one with brass.

Don't forget to safety-wire the three bolts on the saddles that hold the tank up!

Good morning,

Household varnish wont work coating the cork floats, after a day sitting in petrol the varnish fromed carb blocking lumps!

Am trying to modifiy a plastic float now.