When I dropped the tank on my PJ last winter, there looked to be a tar paper material between the straps and the tank. Does anyone know if this was a standard item that I need to replace or if it is normally just metal strap against metal tank?
My second question is does anyone know a source for replacement sending unit?
Todd, I just went through the archives over at P15-D24 and realized you asked a question that I never answered. I measured 126-128 ohms on the sending unit when it was in the full up position. I never measured it at the half way point. I will be removing it again soon so are there any other measurements you would like me to make? You mentioned expensive sending units... who sells then and how much would they cost?
Hi JimCno,
There was some canvas like material between the straps and tank on my car. I think it is for anti-squeak purposes. I left it off when I got things together 15 years ago and have not noticed any problems. You will want a good electrical connection between your tank and the frame for the sending unit to work properly.
Atwater Kent at
http://atwaterkentmfg.com/index.htm
Makes and repairs sending units, but I will have to say that I was not really pleased with the one I purchased from him.
126-128 homes when full up (tank full)? My dash unit reads empty on about 120 ohms, 1/2 at about 37 ohms and full at about 8 ohms. Maybe they reversed the way the units work between 33 and 35.
The Atwater Kent sending unit I got measured 128 ohms at empty, 48 at 1/2 and 3 ohms at full before I installed it. However it started acting erratically by the end of the very first tank of gas.... I didn't record the numbers but when I pulled it out I remember that it seemed to be inconsistent on the relationship between position and resistance in addition to the cork float's shellac coating being softened by modern gas. I wondered when I installed it if I should replace the float with a different material first.
Anyway, if you could measure the resistance at various tank levels I would be very interested in the results. I was guessing that they used the same range of resistance between 1930 and 35 but because of tank sizes everything I have seen shows different part numbers. And, of course, for styling reasons the dash units all have different numbers too.
Your right, 128.2 ohms with float full down:
(https://www.plymouthowners.club/talk/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv76%2FJImCno%2FBluebelle%2FDSCN0034.jpg&hash=9db5c5084e90de8f2ef60bdf72c9e515ce5fd600)
2.7 ohms with float full up:
(https://www.plymouthowners.club/talk/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv76%2FJImCno%2FBluebelle%2FDSCN0036.jpg&hash=f16e4293d093fdb4f168b3c01f10e4933ab955ea)
Just curious. Connect your red and yellow alligator clips together right where they attach to the sending unit. What's the residual reading?
Quote from: Plymouths on October 07, 2008, 06:46:44 PM
Just curious. Connect your red and yellow alligator clips together right where they attach to the sending unit. What's the residual reading??
You want to see if zero ohms reads zero? :)
I think there is enough evidence now to say that the 1933-35 (and probably 1930-35) sending units should read about 3 ohms when full and 128 ohms at empty.
Which is, unfortunately, not a standard that appears to be in current use. So the inexpensive universal style sending units are not going to work well even though they bolt right in to our flange with its five holes.
I guess what I was getting at was the actual resistance down to the last ohm is not going to make much difference. I betcha there is 5 to 10 ohms resistance in the leads and old connections between the gas tank and the dash gauge? I think you're forgetting what's called 'percent error of reading'. I would guess these old gauges are at best 15% in error(and possibly worse) and non-linear to boot. I wouldn't worry about the very last ohm. The system couldn't resolve it on the gauge. Try adding a 3 ohm resistor in series with the gauge line and see what movement you get from the gauge needle. I bet it doesn't visibly move.
Quote from: Plymouths on October 07, 2008, 09:11:13 PM
I guess what I was getting at was the actual resistance down to the last ohm is not going to make much difference. I betcha there is 5 to 10 ohms resistance in the leads and old connections between the gas tank and the dash gauge? I think you're forgetting what's called 'percent error of reading'. I would guess these old gauges are at best 15% in error(and possibly worse) and non-linear to boot. I wouldn't worry about the very last ohm. The system couldn't resolve it on the gauge. Try adding a 3 ohm resistor in series with the gauge line and see what movement you get from the gauge needle. I bet it doesn't visibly move.
You largely correct. At least on my dash unit the needle rests at a slightly different spot with the same resistance if you approach it from one direction versus the other. Apparently there is enough friction in the pivot that the result is some hysteresis in the reading. On the other hand the needle is pretty much on the full mark with 8-10 ohms and reads above full at 0 ohms so there is some difference in readings with a small change in ohms. It is my impression playing with the dash unit and a bunch of (10%) resistors in various series/parallel combinations that the gauge is pretty sensitive to slight variations in resistance when reading between 1/2 and full but it is much less sensitive between empty and 1/2.
So I dropped my tank and found out where it was leaking (I guess I didn't mention in the original post that is why I'm playing with this in the first place). When I fill the tank, the gas comes up through the bottom of the sending unit through that little vent, then works it way out through the electrode that the gauge wire connect to.
(https://www.plymouthowners.club/talk/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv76%2FJImCno%2FBluebelle%2Ffuelsendingunit0013.jpg&hash=cb4f53a5f90cc9bd1327cb9173a8dff2af6da908)
(https://www.plymouthowners.club/talk/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv76%2FJImCno%2FBluebelle%2Ffg.jpg&hash=ffd6fa2fdf7e5aa9eef29c397be3186b3abfb2d0)
Apparently I need to seal that point better. As a matter of fact, I may just pull it apart, add more sealant to the inside (around the screw holes). Then make a cork gasket just to make sure.
So one question is... why would you have a vent hole in the bottom?
Anyone have any suggestions for the best gas resistant sealer?
And... putting the leads on the unit itself has zero ohms, just as Todd figured. I measured the resistance with the float arm at about 45 degrees and got about 25 ohms. I'm not sure that means anything though, I have not hooked it back up to the gauge to see what resistance it reads at half full. I'll try to do that before I put it all together.
Todd, where would you purchase one of the inexpensive sending units and what resistance does it have? One that is inaccurate may be better than one that leaks.
You can get "universal" senders from J.C. Whitney:
http://www.jcwhitney.com/autoparts/Product/Pr-p_Product.CATENTRY_ID:2005714/c-10101/Nty-1/p-2005714/Ntx-mode+matchallpartial/N-10101/tf-Browse/s-10101/Ntk-AllTextSearchGroup?Ntt=ADJUSTABLE+FUEL+LEVEL+FLOAT
However none of them have the 3 to 120 range we seem to need. I am toying with the idea of getting two of the "240-33" range Stewart-Warner compatible and seeing if I can mount both resistor modules on one mount (probably with the floats in opposite directions) and wire them in parallel. That should give a range of 16 ohms to 120 ohms. (You can mount the resistor/sweep unit either way up to allow for which way your dash unit reads). But getting the whole thing into the tank might be a problem.
At present I am running one of the 0-90 ohm units but it goes from reading full to about 3/4 of a tank really rapidly and will never read lower than 1/4 tank so it is almost useless as a fuel gauge.
By the way, I clamped my Atwater-Kent sending unit onto the shelf of my drill press and measured resistance with the float held a three points:
Top (full) 2.8 ohms (float held against a straight edge level with top of sending unit).
Half (center of float 3" down from top): 45 ohms
Empty (bottom of float at 6" down from top): 108 ohms.
If I could only trust that unit to read reliably when it was in the car I'd put it back in.
As to why your unit has a vent on the bottom. I am guessing that you can't keep gas out of the rheostat area, so you might as well allow it to get out easily. That would also mean that the rheostat section will be in the gas saturated atmosphere which is too rich a mixture to easily ignite. If it did not have the vent it would have gas vapor in it anyway (through the rod entry hole) but might have a low enough saturation to be easily ignited.
have you tried www.fuelsender.com they repair and supply fuel sender units
Quote from: elmo54 on October 08, 2008, 03:42:34 AM
have you tried? ?www.fuelsender.com? ? they repair and supply? fuel sender units
I had not heard of them. Will add the to my list of "potential vendors"