Fuel Gauge Questions (1 Viewer)

MyToy72

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I have been having some issues with my gauges now that I have my truck on the road. I was able to use the below thread to correct my Temp Gauge issue, Thanks Rudi. My question. My fuel gauge has been tested per Rudi's thread and it works fine. I installed a new tank and a new sending unit from CCOT during my rebuild. ON a hunch from this thread I pulled the new sender out and put in my old one that came with the truck. BAM, it worked like a charm. It appeared to register the correct amount of fuel in my tank. I tested it before hand using the 3 watt bulb trick from Rudi. Can anyone tell me why all the NEW sending units etc... will not work with the gauges in my cluster? My challenge now is the old gauge does not completely seat properly and I can't grind the edge of the tank due to metal shards and explosion concerns. Will have to noodle that one for a bit. Would love to hear if others have run into this and how they have compensated. I did try double grounding etc... and this did not work.
My rig is a 12/72 FJ-40

https://forum.ih8mud.com/threads/clusters-gauges-speedo-odo-meters.544543/

Testing old Fuel Gauge-1.jpg


Testing old Fuel Gauge-2.jpg
 
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Have to use the correct sender for the gauge, the sender output varies. Check the sender output with an ohm meter, in the empty and full positions, compare them.
 

MyToy72

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Ok, can you give me an idea of how to do that? Do I put the OHM mete in the loop instead of the light and take the readings?
 

bj40green

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Hmmmmm, I see a 2nd gen. fuel sender, but your truck is a Dec '72 right?
That means that you have a 3rd gen. cluster because the change over from 2nd to 3rd was in Sept. 1972.
Please post pics of your gauge cluster and both senders to figure out what you have.
Which sender works and which not/

The difference is that the 2nd gen has the VR inside the Fuel sender and the 3rd gen. has the VR inside the Fuel gauge. Those 2 don't mix.

Rudi
 

MyToy72

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Rudi, thanks for your input. Ok, I have pics of the two fuel senders and the cluster front and back. The sender out of the original 12/72 vehicle seems to work, the only issue is it does not seat all the way in the tank, but sticks up about 1/8 of an inch or less. Unless I take the tank out and drain the gas etc... and grind the opening I am going to try to make a gasket of some time to keep the fuel from spilling out. Pictures to follow.
 

MyToy72

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Hmmmmmm getting errors when trying to load photos. Have re-sized them etc.... will try again in the AM seems like something is up on the site. Just an error message that "file can not be loaded"
 
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Flasher indicators in the dash = early cluster. A 12/72 should have flasher indicators in the cluster, but that is just trivia.

At this point you have two choices: Get a later gauge/cluster to match the later sender, or make the early sender fit the later tank.

It doesn't take much grinding to make them fit, the time is in taking the tank out and making it safe to work on. The inner sheet metal lip is where the gasket seals, so don't want to take it all off, only needs ~1/16" removed. The outer ring where the screws go is only tacked on, will not seal.


Unfortunately, didn't take a pic of it cut, but some pix here: the DSRTRDR is getting some TLC . . .
 
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How we make them safe to work: Drain the fuel, snatch the tank out. Tape/plug the holes, put ~.5gal of denatured alcohol and slash around well, this converts the gas to water soluble, rinse out. Put some detergent and water, shake, foam it up, rinse out, at this point there should be little/no detectable gas smell.

Fill with water and do the work. When done, drain and rinse with denatured alcohol a couple of times to help it fully dry. Likely overkill, but explosions suck?:hillbilly:

Alternatively, if you have the stuff, can purge the tank with inert gas, we use nitrogen, but CO2, whatever will work. As long as there is no oxygen, it cant boom.
 

bj40green

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Your cluster (2nd gen.) matches the 12/72 sender. A bit strange because the change over was in Sept. '72.
The sender from CCOT is for later (3rd gen.) clusters and will not work with your cluster.

Rudi
 

MyToy72

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Ok Update, Just in from the garage. Sorry no pics, but will try to send some tomorrow night. I ground the lip on the fuel sender ridge where it attaches to the fuel sending unit ever so slightly so it was tapered and fit better in the hole. Stopped at NAPA and bought some 1/8 in cork gasket sheets. Took the new rubber gasket and made a cork gasket to fit. I also stopped and picked up 5 #4mm screws that were 12 mm long, the original ones were more like 8mm long. Put the thing back together with both the rubber and cork gasket I made and it seems to be tight. I added some gas from a spare can and the gauge seemed to move up from where it started. Good sign I think. I will let you know tomorrow after some test driving etc... if it indeed is working for sure. I was thinking of also using "Right Stuff" gasket sealer, but will leave the passenger seat out and drive it a bit to see how it goes. If it does leak out I may have to do that until I get the patience and time to do as ToolsRUs said in his post.

Interesting stuff to say the least.
 
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Rudi, thanks for your input. Ok, I have pics of the two fuel senders and the cluster front and back. The sender out of the original 12/72 vehicle seems to work, the only issue is it does not seat all the way in the tank, but sticks up about 1/8 of an inch or less. Unless I take the tank out and drain the gas etc... and grind the opening I am going to try to make a gasket of some time to keep the fuel from spilling out. Pictures to follow.
some pics of fuel gauge testing----

fuel sender test1.jpg


fuel sender test2.jpg


77 FJ40 tank vs sender resistance.jpg


IMG_1175.JPG
 
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Gasket sealer will not hold up to gasoline very well, silicone even less. Best to leave it to the gaskets. I'd make a copy of the original out of thicker rubber so you don't have an extra junction.
 

MyToy72

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Just a quick update. I did the modifications as I noted and all seems to work. Will try to find some time to snap some photos but have been chasing grounding issues of late.
 
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I'm not sure what kind of sending unit I can use on this fuel gauge. I looked at all the different dash clusters and the closest one I saw was a 1974 from Australia, but it had a 30 amp ammeter and mine has the 50 amp ammeter. Can I use a Centroid unit or does this gauge have the VR that will cause problems? I have a marksoffroad fuel tank that I found online. I think I'd prefer to use the centroid because from what I understand it is much easier to install in the marks tank. Any input would be much appreciated. My rig is a 5/72 but the dash cluster is from another vehicle. Below is a picture of the dash cluster if that helps.

Kind regards,

Michiel

IMG_4294.jpg


IMG_4243.jpg
 

bj40green

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The voltage for the FUEL sender is regulated by a VR inside the FUEL gauge.
You can use #83320-60050 (short lever) for up to Dec. 1978 or #83320-60051 (long lever) Jan. 1979 and later.
The short lever is for tanks inside the cabin, the long lever is for tanks under the floor.
The resistance range is the same.
gauges and senders.JPG


Rudi
 
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Bedankt Rudi,

Comparing the diagram you posted with my dash cluster it looks like a fourth generation. I'll get the long sender ASAP. Thanks for your help, you're a wealth of knowledge.
 

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