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Gas gage sending unit

snamelc

snamelc

Donation Time
The gas gage in my '62 Series II Alpine jumps all over the place and is not reliable. Apparently the sending unit circuit relies on the pivot shaft that the float is hooked to for ground. I have no idea what (if any) method the designers used to ensure that this makes a good ground but right now it doesn't. Even if there is a tiny graphite follower like the one in the steering wheel for the horn, I can't see any way of repairing it so I by-passed it with one end of a small wire hooked to the case and the other to the float arm. I then tested it with a VOM and got 1.2 ohms to 87.4 ohms, rock solid. My question is, am I setting myself up for an explosion if the wire comes off or am I safe? When Boeing had this problem in their fuel tanks on the 747, they had a wire in the tank that was to have only 12 or so volts on it and it was considered safe but they got a short to a much higher voltage that resulted in an explosion. We, of course, have nothing in our cars higher than 12 volts. Opinions? Other solutions?

Bill
 
T

Tom H

Platinum Level Sponsor
Bill, sounds like a great solution to me. I can't see any way that the wire you added, if it came loose, could create a greater likelihood of spark than the original ground thru the shaft.

But I am curious as to how you attached the wire at each end. I assume you used stranded wire for maximum flexibility.

And note the original design relies on the wiping action of the moving pivot to constantly clean the contact surfaces. On the SV sender there is also a spring around the pivoting shaft and some have felt that it provides the contact. But I am convinced the pivoting shaft is the contact and works fine- usually. Maybe some additives in some gas cause more corrosion there?

Tom
 
snamelc

snamelc

Donation Time
Tom:

Just to test the method, I used a small single strand wire that I wound into a coil for flexibility. For one end I drilled and tapped a hole in the cast housing to accept a 6-32 screw and the other, I clamped to the float rod since you can't solder to steel. I'm thinking that before I install it back in the gas tank, I'll go looking for a braided copper wire similar to the ground wire you find in most distributors.

Bill
 
T

Tom H

Platinum Level Sponsor
Sounds great. A small gauge braid would be perfect. But I think about 22 Ga stranded wire, especially if you can find fine strands (like 16 strand), and again make it a couple loops. You might also consider cutting up some old test leads with very flexible wire. And when you clamp it to the float clamp it as close to the pivot point as possible - min flexing and min effect on the float weight & calibration.

Tom
 
C

chazza

Donation Time
snamelc said:
... I clamped to the float rod since you can't solder to steel.

Bill
Click to expand...

You can solder to steel with tinsman's solder 60/40. Make sure that both pieces have been mechanically cleaned; use an appropriate flux; use a well heated bit, or a very soft oxy flame,

Cheers Charlie
 
snamelc

snamelc

Donation Time
Charlie:

I think I'll give solder a shot... I have some 60/40 and some good flux. Also, I'll make the joint as close to the pivot as I can. (First, some practice joints!) Paul: I think I'll stick with the by-pass wire... cheap and I don't like relying on passing current through a rotating part, even though the unit probably worked fine for the first 30 years or so :)

Bill
 
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