Fuel Sender Repair

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crumast

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Does anyone have a line on a shop which can repair a fuel sender? I've got one that's acting up. I'm sure it's a standard Stewart Warner automobile unit from the day(1950). It's designed for 6 volt, as a correct resistor is required in the circuit to the switch. Tom Robinson
 
Unfortunately, Lock Haven didn't pan out, so I'm still looking. Tried to get a source through EAA, but they never got back to me. I may have to throw myself onto the mercy of the World Wide Net. Tom Robinson
 
I had to deal with sender's on this plane, did not know before this there is three types of ohm sender's 0-30, 60-90, 90-120 ph? After not finding the old correct ones I found a left and right with adjustable floats for heights of tanks from Summit racing, once all the senders where same ohm's I changed the fuel gauge to match and problem was solved. These where all 12 volt sender's and had less than two hundred in all three sender's and gauge. Hope this helps, and we are never to old to learn something new!
 
I sent the sender to Keystone Instruments, after a couple of guys at the local airport recommended them. At $145+postage, not cheap. Easier than new senders. Turn around was only about a week, which surprised me. I’d use them again. I guess they do all kinds of instrument repair.
They’re at http://keystoneinstruments.com/
(570)748-7083
Tom Robinson
 
Tom,

What were you seeing on yours? Mine (14-19-2) reads about 3/4 when full. Not sure what they read empty yet. Full, the sender is at about 35 ohms. When shorted the gauge reads about 9/10. When open goes below 0. I used a potentiometer and get the gauge reads exactly 0 at 106 ohms. I am thinking that I might have an issue with both the sending units and gauge both.

Mark
 
I have one gauge for the three tanks, with a three-position selector for the gauge. With the aux tank selected the indication was erratic. Especially with a full tank. I found the resistance went way high in a full-tank condition. Don’t recall the numbers. Far higher than compared to a midrange reading. The guy at Keystone thought the resistor in the sender probably needed cleaning. Whatever he did worked.
Readings for each wing tank were reasonable.
Tom Robinson
 
I didn't see this topic until now, but if anyone else needs to replace their senders, get a pair of Stewart Warner 391B-F senders. They don't have the metal floats like the originals, but times have changed. They are a perfect fit, and I believe even the screw holes match the originals. Just measure your tank height accurately when you adjust the float height. You may have to go back and adjust it again to fine tune. No biggie, if you have removable sender covers on your wing. They are 33.5-240 ohms, so just make sure your gauge matches. I bought a new Stewart Warner gauge that matched my old one. And yes, most of the old triple-tails probably had the 12v-6v resistor, since all the automotive stuff was 6v back then. Installed new 12v gauge and senders, removed resister. Done.
 
On mine, it’s between the fuse panel and the switch for the fuel gauge, and located behind the instrument panel. It’s a wire-wound resistor, that measured about 37 ohms. Tom Robinson
 
I'm in the process of changing the senders and gauge. All originals are marked Stewart Warner. The 2-1/8" automotive style gauge has a black bezel and black face with white markings and white needle. The senders in the wing tanks are both "right handed" so the one in the right wing is clocked differently, the float arc is rotated 36 degrees into the forward part of the tank, the one in the left wing is straight out toward the wingtip at the thickest part of the tank. The mount has 5 screw holes. 360/5=72 degrees per hole of rotation. The sender was turned 2 bolts clockwise, 144 degrees Brain teaser! Maybe it does not read the same as the sender in the other tank due to the different arc of the float?
The resistance from empty to full is about 116 Ohms to about 8 Ohms, and 'scratchy' which is probably why the gauge needle swims around. The aux tank sender is 'right handed'. The mount is easily accessed. It's at the top of the tank, close to the fuel filler. Just remove the rear seat cushions, its right behind the top of the seat back cushion.
I elected to go 'all new' and ordered one M391A-F 'left handed' and two M391B-F 'right handed' senders currently $34.99 each, and a M-284-M gauge $54.99 (the stainless steel bezel gauge was $15 cheaper, go figure)
I'll be searching for that wire wound resistor and worrying about the continuity of the selector switch...
 
Those worked for me a couple years ago, the only problem I have when some one hops in and says you have 1/4 tank of fuel not knowing the angle of tanks till airborne then it will read better unless it is all the way full then they say full.
 
well...I get to Eat Crow. :oops: Jarod was correct.
Both main wing fuel senders are M391B-F, right hand units. The 5 mounting screw holes are not evenly spaced, and the gasket has a small hole between the two holes that are slightly farther apart. This goes under the Stewart Warner logo.
The float follows the same arc in both tanks using the same part number by drilling the mounting screw holes specifically for the M391B-F sender. The arc of travel places the float just forward of the fuel filler.
Now I am short one M391B-F, and have an unusable M391A-F. (All three tanks use the same) :shock: The IDEA that Bellanca would cleverly arrange to use one common fuel sender for all three tanks! :idea:
 
I will be replacing my troublesome fuel quantity system with Mitchell gauges and VDO Reed Switch senders, all matched to 240-33 ohms. All three tanks!
 
shipchief,

Did you have to do anything to adjust or tune these? I bought the M391B-F senders and they fit perfectly. It seems like the gauge does not read correctly still. I am not sure about this yet, as I am still adjusting the floats and height, but on the first pass, it seems like it won't be right. Information on anything you needed to do to make this work will be appreciated.

Maybe I need to remove the resistor? Where is the resistor located?

Mark
 
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