'66 Valiant: Gasoline guage acting abnormal

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Scooper

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Location
Douglas, Georgia
1966 Valiant Sedan.
What it is doing: Gas guage never reads 100% full, even when completely topped up. Seems like it is somehow off adjustment, since it seems to stay in the "low tank" and "empty" ranges for longer.

What I have tried:
- New sending unit (this was replaced before it began acting up, and worked perfectly fine for some time)
- New fuel tank
- New wire running to sender
- Replaced all fuses
- Replaced circuit board of cluster
- New cluster AND main voltage regulators
- Cleaned all grounds as well as wired in a master ground
- Sending unit is grounded
- *MIGHT* have replaced the Gasoline guage, but I cannot remember

Any thoughts? If I recall more that I have done, I will post. I've had my hands on most every nut and bolt on the car, so have the capacity to fill in needed details.
 
If you had replaced the original sender in the fuel tank you would recall the reproductions look nothing like what you removed. They will hold the gauge needle at full for extended period and later drop like a hammer to 1/4 tank or less.
If you replaced the instrument voltage regulator ( plugs into the circuit board ), it may be a solid state regulator that puts out approx' 5 volts at 1 to 1.5 amps. That can be why a full tank doesn't register full at the gauge. Some vendors like RTE claim their solid state regulators with advanced circuity will better mimic the original mechanical limiters. I never owned one so I don't know. All I know is, The mechanical limiters 12 volt supply was not fused. When its points were closed the current going through its resistor winding was a pretty hot shot. The thermal gauges would heat up fast, respond quickly, and show as good as they ever did, going all the way back to when they were use in 6 volt charging systems.
The basic solid state ( 7805 chip ) regulator cannot do that. Up to 35 volts in will result in same steady voltage and amperage output. Gauge needles respond slower and they level off at a little bit lower. Bottom line, none of the modern electronics on top of OEM gauges perform like OEM. So how do they get away with selling us "whatever" for our classics? These thermal gauges always were simple basic range indicators anyway. Their gauge screens have only hash marks. No numbers for actual temperature, oil pressure, gallons onboard. You're not in todays Lincoln that will show you 11.5 miles to empty. When driving a classic, after the failed OEM electronics are replaced with whatever we can find/buy, gas gauge says 1/8 tank, only 8 gallons added to full it completely, Over fill the neck, gauge still doesn't show full... learn to love it?
OK... wait one more minute, If you float does have a crack and filling with fuel, it will get worse once its saturated enough to hold the needle at empty no matter how much fuel you add. At that point you will need a new float and a new sender seal. 2 vendors, 2 shipping costs, will be about the same as entire new sender from Rockauto.
One more option is adding another piece of modern electronics called Meter Match. At one time it could be had for about 55 USD but its my understanding that it was purchased by another vendor and the price went up. How much will you spend to have more accurate gauges?
I put a question mark by "learn to love it" for a reason. I top off the tank of my 67 fish almost every time I leave home. I'll hear "nice ride" or similar comment long before I reach a cruise-in or car show. They don't need to know my gauge readings suck. I learned to love it. Sermon over.
 
If you had replaced the original sender in the fuel tank you would recall the reproductions look nothing like what you removed. They will hold the gauge needle at full for extended period and later drop like a hammer to 1/4 tank or less.
If you replaced the instrument voltage regulator ( plugs into the circuit board ), it may be a solid state regulator that puts out approx' 5 volts at 1 to 1.5 amps. That can be why a full tank doesn't register full at the gauge. Some vendors like RTE claim their solid state regulators with advanced circuity will better mimic the original mechanical limiters. I never owned one so I don't know. All I know is, The mechanical limiters 12 volt supply was not fused. When its points were closed the current going through its resistor winding was a pretty hot shot. The thermal gauges would heat up fast, respond quickly, and show as good as they ever did, going all the way back to when they were use in 6 volt charging systems.
The basic solid state ( 7805 chip ) regulator cannot do that. Up to 35 volts in will result in same steady voltage and amperage output. Gauge needles respond slower and they level off at a little bit lower. Bottom line, none of the modern electronics on top of OEM gauges perform like OEM. So how do they get away with selling us "whatever" for our classics? These thermal gauges always were simple basic range indicators anyway. Their gauge screens have only hash marks. No numbers for actual temperature, oil pressure, gallons onboard. You're not in todays Lincoln that will show you 11.5 miles to empty. When driving a classic, after the failed OEM electronics are replaced with whatever we can find/buy, gas gauge says 1/8 tank, only 8 gallons added to full it completely, Over fill the neck, gauge still doesn't show full... learn to love it?
OK... wait one more minute, If you float does have a crack and filling with fuel, it will get worse once its saturated enough to hold the needle at empty no matter how much fuel you add. At that point you will need a new float and a new sender seal. 2 vendors, 2 shipping costs, will be about the same as entire new sender from Rockauto.
One more option is adding another piece of modern electronics called Meter Match. At one time it could be had for about 55 USD but its my understanding that it was purchased by another vendor and the price went up. How much will you spend to have more accurate gauges?
I put a question mark by "learn to love it" for a reason. I top off the tank of my 67 fish almost every time I leave home. I'll hear "nice ride" or similar comment long before I reach a cruise-in or car show. They don't need to know my gauge readings suck. I learned to love it. Sermon over.

I have just swapped the original regulator for the cluster back in. No change.
 
Key phraise "new sending unit"
None are accurite. None Except for the original ones
 
I changed over to a 7805 chip. Now the gauge works, but........ I have an aftermarket sending unit so it works like it works.

I reset my trip meter and track miles. When I get to 125 miles, I start thinking about stopping for gas.
 
If you had replaced the original sender in the fuel tank you would recall the reproductions look nothing like what you removed. They will hold the gauge needle at full for extended period and later drop like a hammer to 1/4 tank or less.
If you replaced the instrument voltage regulator ( plugs into the circuit board ), it may be a solid state regulator that puts out approx' 5 volts at 1 to 1.5 amps. That can be why a full tank doesn't register full at the gauge. Some vendors like RTE claim their solid state regulators with advanced circuity will better mimic the original mechanical limiters. I never owned one so I don't know. All I know is, The mechanical limiters 12 volt supply was not fused. When its points were closed the current going through its resistor winding was a pretty hot shot. The thermal gauges would heat up fast, respond quickly, and show as good as they ever did, going all the way back to when they were use in 6 volt charging systems.
The basic solid state ( 7805 chip ) regulator cannot do that. Up to 35 volts in will result in same steady voltage and amperage output. Gauge needles respond slower and they level off at a little bit lower. Bottom line, none of the modern electronics on top of OEM gauges perform like OEM. So how do they get away with selling us "whatever" for our classics? These thermal gauges always were simple basic range indicators anyway. Their gauge screens have only hash marks. No numbers for actual temperature, oil pressure, gallons onboard. You're not in todays Lincoln that will show you 11.5 miles to empty. When driving a classic, after the failed OEM electronics are replaced with whatever we can find/buy, gas gauge says 1/8 tank, only 8 gallons added to full it completely, Over fill the neck, gauge still doesn't show full... learn to love it?
OK... wait one more minute, If you float does have a crack and filling with fuel, it will get worse once its saturated enough to hold the needle at empty no matter how much fuel you add. At that point you will need a new float and a new sender seal. 2 vendors, 2 shipping costs, will be about the same as entire new sender from Rockauto.
One more option is adding another piece of modern electronics called Meter Match. At one time it could be had for about 55 USD but its my understanding that it was purchased by another vendor and the price went up. How much will you spend to have more accurate gauges?
I put a question mark by "learn to love it" for a reason. I top off the tank of my 67 fish almost every time I leave home. I'll hear "nice ride" or similar comment long before I reach a cruise-in or car show. They don't need to know my gauge readings suck. I learned to love it. Sermon over.
The key is:
- New sending unit (this was replaced before it began acting up, and worked perfectly fine for some time)
which makes me think something happened, thus the leaky/sinking float.
 
The key is:

which makes me think something happened, thus the leaky/sinking float.

The float will certainly be on the agenda. I wish my mental timelime of work was clearer so I could precisely pinpoint what action was taken before the trouble occurred, but, alas, such is not the case.
 
new sending units for our early a bodies suck- plain and simple- i have the oem ones that go bad repaired because they are the only ones that will read correctly . If you compare side by side they are totally different and will not read correctly due to the arm being in the wrong place- closer the tank opening vs the original towards the back of the tank.
 
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