Topic: NOS sending unit stopped working

[Hipo giddyup]

So the gas gauge in my 67' has been fluctuating recently, and now will not read at all. If I place a test light between the sending unit tank feed and ground it between the sending unit post and outer ring on the tank, then it works? Any suggestions on how to salvage this NOS sending unit? Weird how the test light makes it work, but if I place a ground between the post and ground it to the tank or sending unit ring the gauge always stays on full? Uh

[67gtasanjose]

Try running a temporary jumper ground wire to the tank unit itself from a "known good" ground. It is possible the tank unit lost it's ground or the tank itself isn't grounded correctly somehow (paint buildup or sealant?).
That's my first thought given what you wrote.

Richard

[Hipo giddyup]

So a wire from say, the frame to the unit( maybe attachment ring ). Got it, will try this tomorrow night and see if it works.. BTW, if i ever have to pull the unit, will it come out in front of the transverse muffler or do i need to pull the tank..?. Thanks!

[Bob Gaines]

So a wire from say, the frame to the unit( maybe attachment ring ). Got it, will try this tomorrow night and see if it works.. BTW, if i ever have to pull the unit, will it come out in front of the transverse muffler or do i need to pull the tank..?. Thanks!

hopefully the ground experiment will indicate you need to bare some metal to make good contact (easy fix). If not and you have to pull the sender to further diagnose , drain the tank by means of the drain plug or use a electric pump to empty the tank from filler neck (my typical way) after once stripping the threads of a drain plug. The sender will come out without pulling the tank. The wire wrapped around the sender sometimes gets corroded and does not make good connection between it and the contact that moves along it's length when the float goes up and down. Sometimes you have to lightly scuff those contact surfaces for the sender to work properly. More a issue with a gummed up old gas covered one then a NOS one but I would at least give it a try if you have to pull it. You can manually work the sender by grounding it and moving the float while having some one check the gauge for function. If a wire is broken in the wrapped length there is a more difficult fix. I hope you don't have to go that far but if truly a NOS C7 5/16 sender it is worth the trouble because they are rarer. C8 3/8 senders are much easier to find . If you get to that point I will do some more typing. Best of luck.

[Shasmu]

 If the gauge works with a test light hooked to ground, chances are good that the float has a breech in it's outer membrane, and has filled with fuel. Air pressure and temperatures cause the float to expand and contract,this effect is often coupled with electrolysis of dissimilar metals where the plated steel hook holds the float to the sender. Eventually the thin brass skin of the float ruptures from metal fatigue, and a pumping action ensues, causing the float to take on fuel, 'till it sinks. .
  Plastic aftermarket floats often develop a leak at one end, where the ''bellybutton'' is melted to form a plug.
 To remove the fuel sending unit's lock ring, (once the tank is empty) use a hammer and a piece of brass (to avoid sparks), and coax the lock ring counter-clockwise. Test light should flash a fairly consistent cadence if the original electro-mechanical instrument constant voltage regulator is functioning correctly.Modern transistorized cvrs will cause a weak but steady glow of the test light.
 The o-ring is usually replaced when the sending unit is re-installed. Coat the o-ring with petroleum jelly, ( Vasoline) to hold it in place during assembly.

[Hipo giddyup]

Awesome guys, thanks for the feedback. I guess I know what I"ll be doing this weekend.