length of fuel sending unit arm?

[Frank's 49]

I am trying to find a sending unit for a 1949 B!B.  On Ebay I have found a bunch of units which are for the car side, but the seller claims they are not for trucks (or station wagons).  I can't see any difference by just looking at the photos.  But they have several different units, which appear identical, but for different year ranges (and prices).  

I asked "what is the difference in the units, and why don't they believe they won't work on a truck?".  The reply was "how long is your arm"?.

Despite the obvious pun, I wonder if anyone on the forum has a measurement for the "arm" on the sending unit for a B1B pickup?  

I really don't want to take out the seat and remove the floor and the unit, just to get a measurement.  OK, so I am lazy , but when I do remove it, I will make an "access hole" so I at least don't have to remove the entire floor next time.  The woody does not have a nice neat access hole in a metal floor.  The floor is made of wood and I will have to cur a hole.  Or drop the tank (no!) 

 

[The Oil Soup]

I recently changed mine with a sender from a jeep Cherokee. I will post photos because it needed to be lengthened. It is obvious how long it needs to be once you know the distance the float must travel from full to empty.

[greg g]

Single wire or two wire????

 

[Frank's 49]

I just looked at a diagram in the Pilot House Knowledge site and the 18 gal tank is shown as 12 5/16 inches from top to botton on the 108 WB, so I guess 12 inchs ought to do it? 

[Frank's 49]

4 minutes ago, greg g said:

Single wire or two wire????

 

It is single wire.  

Oil Soup..  How much did the Jeep unit cost?  The one I am looking at on EBay is $79.   

this is the one I am thinking will work  (wish they would incude the length) 

http://www.ebay.com/itm/1949-1950-PLYMOUTH-DODGE-DESOTO-CHRYSLER-GAS-FUEL-SENDER-GAS-TANK-SENDING-UNIT-/172658655013

Edited June 2, 2017 by Frank's 49
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[Frank's 49]

 

43 minutes ago, The Oil Soup said:

I recently changed mine with a sender from a jeep Cherokee. I will post photos because it needed to be lengthened. It is obvious how long it needs to be once you know the distance the float must travel from full to empty.

 I just heard from the e-bay seller.  His unit measures 8" which i am sure is too short.  But... if it is cheaper then the Jeep I still might get one and lengthen it.  How did you add length?  and how long was the arm?  

I figure if the arm is shorter than stock, the worst case will be I will be left with some "reserve" gas when the gauge says empty.  

 

[Merle Coggins]

I used a sender from Roberts. The arm was shorter than the old unit, but it seems to work just fine. I figure if it doesn't reach the bottom of the tank then it gives me a "reserve" when the gauge reads empty.

Old unit on the left... Roberts unit on the right

Also, to ensure a good ground for the sending unit I added a ground stud. I drilled a hole off to the side and inserted a machine screw, with a bit of sealant. This way I could add a ground wire to the chassis and not rely on the tank mounting for a ground path.

Edited June 2, 2017 by Merle Coggins

[Frank's 49]

Merle;   like you I figure a short float rod will just leave me with some emergency gas.  I also added a ground to the unit currently in the truck.  Just used a small self tapping machine screw.  I like your fix better.  Unfortuately the potentiometer and the float on my unit are both shot.  

I am going to try one from vintageamericanpartsco and see what happens.  

 

[The Oil Soup]

The jeep unit was about $35. I had one of the units than ran $85 and worked for 20 minutes or so, and also saw on the forum how they dealt with someone who had problems with it (accusing them of over tightening the screw) so I opened it up and found the rheostat wire had unwrapped from around the terminal because it was not soldered. I will post photos later today. A length of stiff wire can be used to extend it, it is a single wire unit. The range on it is 78 to 10 ohms. It shows full fine not sure about empty. Haven't done the "carry a can of fuel in the truck until it runs out" yet.

[Frank's 49]

2 hours ago, The Oil Soup said:

The jeep unit was about $35. I had one of the units than ran $85 and worked for 20 minutes or so, and also saw on the forum how they dealt with someone who had problems with it (accusing them of over tightening the screw) so I opened it up and found the rheostat wire had unwrapped from around the terminal because it was not soldered. I will post photos later today. A length of stiff wire can be used to extend it, it is a single wire unit. The range on it is 78 to 10 ohms. It shows full fine not sure about empty. Haven't done the "carry a can of fuel in the truck until it runs out" yet.

Well, I might have screwed up, but I ordered one that was $67, including the shipping.  We shall see.  

My Dad just carried some spare gas for years.  Except the time he ran out on the paper route at 4 AM and had to walk 2 miles carrying gas in two open-top quart oil cans.  He said they got unbelievably heavy!! 

[The Oil Soup]

The first thing I did was make a template of the fuel tank opening. This was to verify that the jeep sender would fit in the opening, with some filing of the sender that fits down in the tank it went in. Next I determined how long the arm needed to be to travel from full to empty. I think that was about 9". The sender is for a full size jeep '70-'79.

 

 

 

 

 

 

 

 

 

 

 

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[jmooner3]

Thanks Soup! I just ordered from amazon for $32 and Prime free shipping. If it works I figure I'm better than $60 ahead of the game. I'm thinking a bend to the shorter arm should get the float closer to the empty end and still allow full travel up to full... Otherwise I'll cut and weld the old unit's arm in place or just lengthen like you did.

Amazon:

Omix-Ada 17724.18 Fuel Tank Sending Unit

 

[wallytoo]

i used a jeep unit too.  there should be a thread somewhere, i posted in it.  paid about $35 for it.  lengthened it by soldering a portion of a paint can bail to the arm.  has worked for years since i installed it.

[Frank's 49]

http://www.ebay.com/itm/172532179057?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I got the one from vintageamericanpartscompany, which is designed to fit automobiles.  The arm was indeed shorter, and the float is a copper float, rather then a cork, but otherwise everything looks the same.  It came with new gaskets and a new locking ring.  I lengthend the arm with a piece of 12 gauge copper wire (plenty strong enough) and added a ground stud as Merle Coggins did.  It fit right in place and and the gauge now reads 1/2 tank, which is about right, I think.  Time will tell if it is good at full and empty.  

Generally pleased with the unit (could have been cheaper, and I think they are missing a bet by not making "truck" units.  By the way, they carry all sorts of other vintage stuff, so the site is worth a peek. 

 

[jmooner3]

Hey guys - Wondering if any of the electrical gurus have seen this one... I got the Jeep sending unit, ohmed it out and it is in the same operating zone as OEM...roughly~8-70 ohms.  I added the ground stud as Merle did (great idea!) and figured I'd test it before install. The gauge reads nothing until float reaches high travel (like if tank were full) and then gauge snaps to "Full" deflection and latches, even if I move float back down it stays at full. Flip key off and it drops... Turn key back on and move the float, no needle movement until it hits where full would be and needle deflects to full and latches.

I'm not clear exactly how the gauge works or is wired, any thoughts on why?  Note, I rewired the truck so it's possible I have something wrong - Could I have crossed up wires somewhere? Again this is the Jeep unit but others have used it successfully and the rheostat appears to be working as designed.

Thanks,

Jay

[Merle Coggins]

The sending unit is basically a variable resistance to ground for the gauge. As the float drops the resistance increases and reduces the amperage going through the gauge. This changes how much pull there is on the needle. 

Maybe your needle is sticking and not moving smoothly causing the jerky movement. Or could it be wired backwards? I don't know how that would affect it. 

Merle

[jmooner3]

Agreed Merle, It's just a variable resistor... I pulled it out of the truck and made the circuit  externally to rule out my harness - bat neg-> sender stud then from gnd stud that I added to the bat +... Simple circuit. It acts as I said before no movement til sender hits full then full deflection on needle. I found the attached (might help others in the future) I pulled my parts truck's gauge and tried - same result.....Points to the sender itself, it dawned on me after, I never asked if others using this sender successfully were 12v or 6v?  While the resistance on ohm meter seems to swing perfectly fine as OEM  is it possible that the voltage/current difference is the root cause of my issues. My truck is still 6v.

Fuel Gauge.pdf

[Plymouthy Adams]

sounds as you have an open in the wire wound resistor....case in point is the fact you have zero reading till it contact the upper peg at which time the circuit is now made to the input...the wiper that is part of the float arm is the segment that goes to ground...so it is either open or you are losing wiper contact to the wire due to distortion...can you read the full resistance across the rivets that lock the resistor to the board and are the wire contact points...if not the wire is open..if you can read this full range...then you are losing contact with the wiper arm pickup

[The Oil Soup]

The gauge should read fine with 12 or 6v. Mine is 12v with an integrated circuit to drop the voltage to 6v. Here is a how to link. You don't need to use the capacitors. https://www.jalopyjournal.com/forum/threads/how-to-build-a-voltage-regulator-for-3.448038/

[jmooner3]

Thanks guys. Plymouthy, there are no external contact points to ohm out, but I hooked up meter and although it does still show the 10-78ohm range I noticed it does jump around with readings in the hundreds of ohms through the mid travel and is sporadic until full travel where it's steady again.  Its evident now that this sender has issues, I'm going to send the sender and try another.

 

[Plymouthy Adams]

ok, sorry thought you had it apart....but yes you have external contact points....just unable to inspect the wire wrapped  that the float arm will travel against...  Read the post to the flange body with your meter with the float in lowest position, this is your total resistance...as you lift the float the resistance approaches zero hopefully on a fairly linear scale

 

I am guessing that your unit is not linear due to wear in the wiper on the float arm, distortion of the phenolic base that the resistor wire is wrapped about and or combination of the two.  If no break, just take it apart and clean the item, adjust for a bit of tension of the wiper to wire contact. 

Edited June 13, 2017 by Plymouthy Adams

[jmooner3]

Got a second sending unit and it works linear now.  I welded in the 4" extension using a piece of wire rod, added the ground stud that Merle did - The issue with the gauge not moving as the float arm moved until full position was simple, the wires were swapped on back of gauge from when I rewired.... ensured I had good ground to case, got circuit wired correctly and it works as it should. Hope this helps someone else!