The Stovebolt Site Forums The Shop Area The Electrical Bay More weird fuel gauge antics on a '50

A problem just turned up with the gas gauge on my 1950, 3604. I bought her just about on empty, and the gas gauge was working fine, it was accurate and had no needle bounce, put 5gal in to get her home and the gauge was registering ok.
Once I got her road worthy again eight months later, I ran most of that fuel out and added another 5gal, which took me up to about a third of a tank. Now, I’m kind of sneaking up on a full tank, which I didn’t want to get stuck with just incase I may have had a leak part way up the tank or a clot which required me to drain the tank.
So I ran a good bit of that load out and added 7gal next time, this brought me up to a little over 1/2 tank on gauge, still steady and no bounce. Now after I’ve bounced her around for a couple hundred miles with no apparent leaks or problems with the fuel lines clogging up I pumped in 10gal and the gauge responded showing a little over 3/4 full. This time once I got her on the road the needle started bounding between the 3/4 full point and full rather rapidly, like there was no damping. After driving it for 50 or so miles with it doing the same thing with no change, I refilled again. I had a longer jaunt planned, almost 80 miles round trip last weekend, so I decided to top it off since I had encountered no fuel system problems. It took just under 10gal to top it off, and when I could hear it up to the neck I capped her off. The gauge shows full, just as you would expect, no bounce. Now I ran out my 80 miles and she should be down a little under the 3/4 mark and I’m getting that un-dampened bounce to full again.
Key off, she goes to empty. Sitting still in the garage she shows a little under the 3/4 mark and is steady.
First thing I tried was removing all the connections and cleaning with wire toothbrush, including the ground connection under the seat from the sender. The gauges were out a couple of weeks ago and every connection was cleaned at that time. An ohmmeter across the sending unit showed that it was varying when I rocked the truck back and forth from 3 or 4 ohms up to 16 or 18 ohms.
My suspicions are that the sender has some corrosion on the resistance unit near the full position. Any more Ideas before I pull the sender out?
Denny Graham
Sandwich, IL

I suspect one of the baffles in the tank is compromised, allowing too much fuel movement around the sending unit. You can check this using a bore-a-scope or small mirror & flashlight. Of course after draining the gas.

Not familiar with the inside of the tank Tiny, and I was unaware that it had baffels in it. Wouldn't that same thing occure at all the fuel levels if a baffel were loose or shifted? this is only happening when the tank is 3/4 or more full. Other wise it is accurate and steady.
Denny Graham
Sandwich, IL

I'm not sure when they stopped putting baffles in the tanks. The reason they did was to minimize the fuel slosh & erratic fuel gauge readings. The baffles in my 38 are fastened to the bottom of the tank with the top inch or so being open & small openings in the bottom for fuel flow. They create a small chamber in which the sending unit lives. If for some reason one of the chamber walls moved slightly at the top (broken spot weld, rust weakened,?) it could keep the fuel stationary at lower levels yet allow excess movement at fuller levels. Just a thought that's fairly easy to check with a mechanic's mirror & small light through the sending unit opening. It doesn't seem REAL likely but it is possible. I would think if it was a loose electrical connection or short it would happen at all fuel levels.

Hey Denny;

Question for you. Why are you looking at your fuel guage when your bouncing down the road, and not looking at the road? (Just kidding)
Does it really matter if the guage bounces when it's 3/4 full? It sounds like it stops bouncing down in the emptier range (?). Myself, I just want to know when it's time to think about a stop at the next gas station. Bottom line - is this really a problem?

My '63 is doing the same thing now that I have put an aftermarket tank under the bed . All was well before the swap .
I have just learned to see what range the needle is swinging from and figure the level is in the middle of that range .
It is fine once the gas level in the tank gets lower .

I'll pull the sender when I get a chance and check it and the insides out.
In the mean time,Ya got a point there Waldo, it is accurate after it drops below 3/4. Just kind of bugs me when something taint workin the way it's supposed to. There is a whole gaggle of things that I could live with and it wouldn't affect the operation of the old gal but my aim is to get it all just as close as it was back in the 50's.
Denny Graham
Sanddwich, IL

i don't know for sure, but it seems the gauge, or more accurately the float, could be in a position that is more susceptible to "bounce" based on fuel level.

since the float follows a radial path as the fuel level comes up, maybe it's just in a more vulnerable spot as the fuel splashes around when you're at 3/4 of a tank then if you're at full or 1/4 tank.

just a thought...

Oke doke, all fixed. To begin with I found what I think is a repro sender in the tank. I’d like to see an original one as a comparison.
But on to the repair. After removing the hollow rivets and disassembling the unit, I found the problem was with the flexible band that completes the circuit from the wiper to ground. It was broken into four pieces. It was made from .004” thick material and I just happen to have some .004” brass material on the shelf so I just made a new band. The wiper and grounding band are held on the float arm axle with a one-way Pal nut. To remove this I used a small diamond-grinding wheel in the Dremel. Assembling the parts with the new band is a simple straight forward process and a new Pal nut from McMaster Carr finished it off. The one other thing I had to make were the hollow rivets just like the original ones. I made a tool up to spin the heads over in the lathe from 3/16” brass tubing and used the same tool to set the rivets when they were installed back on the unit. I tested the range and it runs from 1.9 ohms to 38.1 ohms. Couple of pics here, take a look.
http://rides.webshots.com/photo/2810310490098611668EngTlM
Took it for a ride tonight and the needle was as solid as a rock.
What I save? Bout $60 with the shipping.
Denny Graham
Sandwich, IL

problem with the sender resistance - in one area there's a number of turns shorted, the slightest sloshing moves it above/below the bad section .... jump up, drop back, jump up, drop back

Bill

Denny Graham,

That sure does look like a new plastic assembly. What keeps the long brass strip from blowing in the breeze and touching the metal extension arm?

Good job...is it explosion proof?

Stuart

The wiper, float arm, hub, pal nut and flexible strip are all common to ground. The only thing positive inside the plastic case is the resistance element.
Bill ya must not have read my reply that is posted right above yours or not looked at the pics. I explained and illustrated why the sender was malfunctioning and showed the repair I made to it. The resistance element had nothing to do with it, that and the wiper were just fine, it was a broken grounding strap inside the plastic case that is riveted to the support bracket.
If I had video I could show you a very nice smooth transition from 38.1 ohms down to 1.9 ohms with no skips or jerks or jumps. The gas gauge is back to reading normal and works just fine again, and no bounce, nice and steady.
Denny Graham
Sandwich, IL

was posting at the same time - read it but didn't bother editing .... the jumping musta been similar effect from the broken piece making contact intermittantly ... and it is cheap repro, the original was a stamped tin housing

Bill

Figured that's what happened Bill, sometimes I spend an hour or more trying to compose a reply and I get behind the curve and the discussion leaves me behind.
Yep that's what the problem was and that's what prompted me to get that gawd awful thread goin bout the “exploding gas tank”.
Thanks for the discription of the original sender, that’s what I figured. The first clue was that it looked like they dint have a clutch head driver so they took the screws out with a pair of pliers. If’n ya got one of the originals around I’d like to see a picture of one.
Good day,
Denny Graham
Sandwich, IL

denny, i might be able to post some pictures of an original sending unit this weekend. since your post about gas gauge problems, mine decided to start doing funny things. i guess i'll have to check it out to see what's up but i won't have time to do it until the weekend.

some of us have jobs ya know...

Man I really feel for ya p.j., but you'll get there to, just think, only twenty years to go!
Denny Graham
Sandwich, IL