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BJ8 Fuel Gauge

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Frank C.

Frank C.

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My fuel gauge was repeatedly sticking on full and I had to tap it to get it loose, so I (maybe mistakenly) took it apart to see if I could fix it. In the process I loosened two nuts on the back of the gauge which I found out moves the magnetic poles for the gauge.

Now I don't know how to calibrate them properly. If I knew the resistance of the sending unit I could mock it up on the bench and get things working again.

Any other suggestions?

Thanks as always.

Frank
 
I'm in the same boat -- did the same thing for the same reason. I learned from you that the movement was of the magnetic poles. On second thought, my gauge was not stuck, it would pin on full when I turned on the ignition. I was given a lot of things to check mainly at the sending unit, but I messed with the gauge before I got to those things and messed it all up.
 
Frank, it's dangerous to loosen the two little nuts on the back of the gauge if you don't know to make sure that the alignment "feet" of the two coils inside don't come out of the slots. These feet keep the coils from spinning when you re-tighten the nuts. If the coils spin, you'll break the coil wires and then the gauge is toast until you send it off for repair. How do I know?

The sending unit circuit resistance for a full tank on a BJ8 is around 90 ohms. For emtpy, it's zero ohms. You can get info on how the gauge works, and how to build a calibration rig for it here: https://mgaguru.com/mgtech/electric/fg_01.htm
This is for the Jaeger gauge in an MG, but the construction and operation of the gauges are the same as Smiths. Instead of 68 ohms for the MG, use 90 ohms.
While the test rig allows calibration of the gauge on the bench, I've found that a gauge still requires some tweaking once installed back in the car.
 
Box it up and send it to Nisonger.

There are tasks that are rewarding to accomplish, and others that just aren't worth the time and aggrevation.
 
Thanks Steve!!! This is just what I needed. Luckily I have a long (and so far) cold winter to get this done.

Again, thanks for your quick response.

Frank
 
Or you could learn the basics and repair yourself. I personally never bail out of trying to repair anything even if there is only a remote chance of a positive outcome. The understanding and knowledge gained is more than enough for me. Especially if time is not a significant detriment.
 
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