BiMetallic gauge repair

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Jim Kueneman

Jim Kueneman

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I need to start figuring out how to fix a few of these gauges for our Dart and Valiant. I thought I had this sort of figured out to buy the materials but now I am confused. The '63 the ohms across the gauges was ~21 ohms and the nichrome ended up coming out to about 20 ohms/foot and I see that number around a lot. Now I have a '66 Valiant dash. The fuel gauge measured out to 12.6 ohms so I thought it was likely shorted due to the insulation falling off the nichrome. The temp gauge the wire was burned open so I pulled it apart and unwound the nichrome from the biMetallic tab and it comes out to about 9.6 ohms per foot and assuming that the fuel gauge should be about 12.6 ohms.

That said this means that the Valiant gauges will pull 2x the current of the more common 21 ohms. Does this seem right? These gauges are rather weird the way the needle is connected... the are sort of free floating and have wire hoop that loops through the end of the biMetallic and also through sort of a counter spring. I can see where it may need more heat to move the biMetallic more...

Has anyone rewound their nichrome and does this 1/2 resistance make sense on the '66 Valiant?

Thanks
Jim
 
I'll be watching this one as I have contemplated trying to rewind the heater in Mopar dash gauges more than once.
 
Redfish is the guy who would know. I have never tried to repair/ rebuild a gauge itself
 
I recall seeing numbers like you describe somewhere. (In my memory it was more like 22 and 44 but there were 2 distinct types of gauges)

Any reason not to find good used gauges?
 
Dana67Dart said:
I recall seeing numbers like you describe somewhere. (In my memory it was more like 22 and 44 but there were 2 distinct types of gauges)

Any reason not to find good used gauges?
Click to expand...

Because that is a crap shoot too... the insulation is just plan gone on these old gauges. I am going to strip a parts car tomorrow for factory AC and I also got the entire dash including the cluster so I will have another chance but.... I also install the fancy Real Time Engineering regulator that has fast shut down if it sees currents getting to high to try to protect things if they do go short..
 
There are a few types of these gauges. Most have aprrox' 13 inches of nichrome winding. 1 ohm per inch @ 68F = approx' 13 0hms, and 1.5 ohms per inch @68F = apprrox' 20 ohms. All 3 rally gauges are 20 ohms.
There was a earlier type that had about 3/4 inch of the wire ran lengthwise on the beam underneath the winding. That was so both ends of the wire would be at the upper end of the beam where there less movement.
 
RedFish said:
There are a few types of these gauges. Most have aprrox' 13 inches of nichrome winding. 1 ohm per inch @ 68F = approx' 13 0hms, and 1.5 ohms per inch @68F = apprrox' 20 ohms. All 3 rally gauges are 20 ohms.
There was a earlier type that had about 3/4 inch of the wire ran lengthwise on the beam underneath the winding. That was so both ends of the wire would be at the upper end of the beam where there less movement.
Click to expand...

Is there a replacement for the insulation on the bi-metal strip?
 
6PakBee said:
Is there a replacement for the insulation on the bi-metal strip?
Click to expand...
There isn't insulation on the bimetal beam. There is a very fine insulation on the nichrome wire. Spiral wound fiberglass.
 
RedFish said:
There isn't insulation on the bimetal beam. There is a very fine insulation on the nichrome wire. Spiral wound fiberglass.
Click to expand...

All these years I have been misinterpreting the fuzzy stuff on the beam. Thanks for the clarification, I learned something valuable today. :thumbsup:
 
Does anyone have a supplier for the fiberglass insulated nichrome wire?

Looked on Amazon and did not see anything


I suppose one could get very fine fiberglass and pull out fibers coat the nichrome in lacquer and roll the nichrome in the fibers.

I bet the nichrome in my now DOA IVR wore through the insulation at one of the bi-metal edges made contact and melted or wire through. ( Nichrome was broken in one of the wraps at the edge of the bi-metal)
 
RedFish said:
There are a few types of these gauges. Most have aprrox' 13 inches of nichrome winding. 1 ohm per inch @ 68F = approx' 13 0hms, and 1.5 ohms per inch @68F = apprrox' 20 ohms. All 3 rally gauges are 20 ohms.
There was a earlier type that had about 3/4 inch of the wire ran lengthwise on the beam underneath the winding. That was so both ends of the wire would be at the upper end of the beam where there less movement.
Click to expand...

yup that is what the Valiant has that end run back up under the windings.
 
Dana67Dart said:
Does anyone have a supplier for the fiberglass insulated nichrome wire?
Looked on Amazon and did not see anything
I suppose one could get very fine fiberglass and pull out fibers coat the nichrome in lacquer and roll the nichrome in the fibers.
I bet the nichrome in my now DOA IVR wore through the insulation at one of the bi-metal edges made contact and melted or wire through. ( Nichrome was broken in one of the wraps at the edge of the bi-metal)
Click to expand...
Yeah? nope,,, that wont work. The lacquer would be far too stiff. Movement of the bimetal would be restricted. The lacquer might melt and smoke/smell from the heat. The winding in the mechanical limiters is different too. 50 ohms total resistance in that wire length. I must point out that the spiral wound insulation on the wire is many strands of way less than a human hair. I would unwind it to expose the wire and pinch off the excess fiberglass with fingernails.
Many years ago, Someone said this insulation was a blend of fiberglass and silk. To this day I dont know if that's true or not. Anyway...,
Some of you might go Google searching and find the same guy I found years ago. He can sell you a book of info and/or some wire but... be warned. The wire he has to offer is 1.2 ohms per inch. A little over 16 inches is required to get between 20 and 20.5 ohms. That's a lot of wire to wind into a A-body gauge of 20 ohms. His wire is made for different gauges with a longer bimetal beam.
And beyond that, The service techs 3 level tester is not enough to calibrate a gauge. That was just a tester to say replace the gauge or not. You have to have decade resistance box if you want to prove all the hash marks on a gauge you renewed, especially if you used a different wire.
decade resistance box | eBay
Can this get more complicated? Yep! Solder wont stick to ni-chrome so the wire is tig welded to the head of the stud. These metals work harden when welded. Vibration and movement will cause the wire to break. That is what the dollop of cement like chit on top of the weld is for. Wire movement is away from the weld.
So... Yeah I used that guys wire for a while and managed to fit Approx' 16 inches of it into A-body 20-to-20.5-ohm rally gauges and made them work right. Beam covered nearly end to end with wire.
Thing about classic cars is they should be soooo simple. It's when you get into the engineering of automatic transmissions, and instruments, and such, that you just have to say, "Damn". I learned, fix the water pumps and chit that I can fix, Leave the more complicated to those that do that.
 
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