IMHO I would still check it. It isn't hard and then you are sure that something unintended isn't happening. These old trucks can play games with you.

 

Raising this thread back to the top, I have the same issue on my oil gauge, mechanical reading is a lot higher than the gauge reading. Ross I think the gauge has to be removed to get access to the window for the adjuster correct?

Is it the same procedure on the fuel and temp gauge?

My gauges are NOS and I should have found this and tested before.

JB

 

It is my understanding that on these trucks, the fuel, oil, and temperature gauges are all the same construction, just a different face plate.

 

Yes, the holes are under the mounting plate. I would go very slowly with any adjustments, let each change settle out for a few minutes.

I have an extra set of gauges that I was playing with last winter. Both measure the same resistance (i.e., the heater coils are the same resistance), I have had them open and no signs of abuse. But the manual's test method of a D-cell battery does absolutely nothing to them. I tried 2 - D-cells, got some movement, about half scale. I would be curious what your gauges' resistance values are, JB. Both my Temp gauge and OP gauge are 12.9 - 13.0 ohms.

The gauges for 51-52's all use the same basic mechanism, but some are 180° from others because they are upside-down in the cluster. I imagine for 48-50 they are all the same, although the Temp gauge goes from H to C so it must be backwards.

 

I'd be sure to follow Ross' advice on taking it slow. I was given the same advice. I moved the adjustment wheel very carefully and just a very little. I didn't see an immediate change--so moved it some more--and (less gently) some more, and pretty soon my gauge was wrecked. I was thinking the needle should move as the adjustment wheel moved--like setting a clock--but that, as Ross points out, is not the case.

Jim

 

I noticed the original poster used D size batteries. I got the same result using AA. One adjuster seems to be the zero adjustment and the other is halfway with 1.5 volts. It’s a fine tune but got it. Does it sound like I did it correct?

JB

 

That is correct. Does it read OP closer to what the mech gauge says now?

 

I don’t know yet Ross, I did this with a spare oil gauge, need to swap it in. I tried a D cell battery and got the same result.

I think I am going to need to calibrate all the gauges, I do not know why I didn’t do that to begin with.

JB

 

Could you please measure the resistance before you install it?

 

In the event one is not aware, these gauges do not work on a ohm/resistance model like many of us are accustomed to. The stock sending units use the The King-Seeley (Ford Stock) constant voltage principle. These sending units supply a full 6V through the heater wire in the gauge in the form of a square wave with the duration of the "on" being the variable determining the gauge reading. The longer the duration, the more fuel in the tank, the higher the oil pressure, and so fourth. It is this full 6v of current which heats the bi-metallic strip in the stock gauge that causes the gauge to read via a small gear train that is adjustable as discussed here.

 

I'm very aware of the K-S principles, but the heating wires have a definite resistance. If the heaters have a shorted winding or their resistance has changed, the gauge becomes inoperative. In my case, these spare gauges I have were given to me by a guy who converted to 12v, and "wasn't sure" he had a voltage reducer feeding the instruments. (I'm pretty sure he didn't) If the resistance (heaters) are still good, then perhaps the 12v feed overheated the bimetallic arms, permanently distorting them. I can't see anything else wrong with them, yet they barely function.

 

Ross I am no mechanic, help me on directions to measure for you. I have a good multimeter.

JB

 

Got the gauges reading exactly halfway on 1.5 volts and zeroed out at the gauge edges. See what you think of my starting points, think those are close enough for hand grenades?

JB

 

Looks good!

As far as measuring the resistance, just go across the terminals on the gauges.