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Fuel gauge problems?

nomad

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Wondering what year's of fuel sending units would be compatible. Specifically whether the early sending unit will interchange with the one from 67 to the early 70's. I know that the whole system changed but not what year. I imagine the same time as when a ballast control unit was added. I have a early sending unit modern replacement that has apparently failed and would like to fit a more reliable unit. Don't trust the stuff the usual suspects are peddling.

Kurt
 

dklawson

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I don't know the transition year for the Spridgets but for the Mini it was late 1964. That's when they changed from the magnetic gauges without the voltage stabilizer to the later bimetallic system with the stabilizer.

Things to look for are the gauge needle type and the sending unit resistance. To identify the early sending unit, disconnect the green/black wire from the fuel gauge's "T" terminal. Connect your multimeter between that wire terminal and ground with the meter set to measure Ohms. Use a coat hanger to lift the float. If the resistance increases towards 80 or 90 Ohms, you have an early sending unit. If the resistance drops towards 30 Ohms as you lift the float, the sending unit is the later type. Don't forget to hook the green/black wire back up.

For the gauge, look at the needle shape and behavior. A wide needle with parallel sides is typical of the later bimetallic gauges. The magnetic gauges use a thinner, tapered needle. When you turn the key to the run position, an early gauge's needle will "snap" quickly to position while the later bimetallic gauges will slowly climb to their reading.

In general, you cannot mix and match components because the early and late sending units have very different resistance ranges and change resistance in opposite directions as you go from full to empty.

Regardless, if you don't mind ordering from overseas, there is a solution for what you want to do. Visit the Spiyda Design website in the U.K. and consider buying their "Gauge Wizard". (I am posting a link below). The gauge wizard can match almost any sending unit to almost any gauge. That includes ones that work in different directions with different resistance ranges. The owner of the website says he developed this product to address mixing and matching gauge system components.

Link to Spidyda Design Gauge Wizard

https://www.spiyda.com/fuel-gauge-wizard-mk3.html
 
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nomad

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Thanks Doug, I have a Spiyda conversion for the tach so am familiar with them. I do know that there is a big difference between the systems but suppose I'll end up springing for another aftermarket since they are not expensive.

Anyone have an early one [58 to 66] they could part with??

Kurt
 

Desert Rat

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Hey Kurt, if you have an original sending unit simply have it rebuilt. I had really bad luck with the replacement sending units dying on me so when I had my gauges restored Morris at West Valley Instruments restored my sending unit and it's been flawless. Obviously restoring the original is more than buying a replacement but mine has never been as accurate as it is now and I don't have to drop the tank every couple of years to change out a dead unit. The replacement units cannot be rebuilt but the original Smiths unit can.
 
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nomad

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Turns out that the PO did have an original sending unit and that my problem was the bent up tank only partially bolted in wasn't making a good ground. New tank bolted up and the gauge appears to be reading correctly. The PO that put this car back on the road raced Spridgets and I'm wondering if the bent tank came from a track excursion with his race car. Bolted in because it was there!

Kurt
 

JPSmit

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Glad the gauge worked well! In terms of the origin of the bent tank, I must reluctantly admit that I have a "floor jack handle shaped dent" on my tank. :rolleyes:
 

dklawson

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Not British... but my wife used to own a great VW Rabbit. She ran over a retread that came off a semi-truck. The retread put a severe dent in the tank reducing its capacity by about 2 gallons.
 
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nomad

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Doug, in the midwest, we call those semi tire strips, "Alligators". They can bite you!

Kurt
 

JPSmit

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Not British... but my wife used to own a great VW Rabbit. She ran over a retread that came off a semi-truck. The retread put a severe dent in the tank reducing its capacity by about 2 gallons.

100 years ago a friend had a Rabbit - the vent got clogged and the Fuel pump literally sucked the tank in on itself
 

dklawson

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100 years ago a friend had a Rabbit - the vent got clogged and the Fuel pump literally sucked the tank in on itself

I tried that in reverse. I tried to plug all the connections and slowly add compressed air to pop the dented tank back out. It didn't work.
 
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