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Looking for a new (gas tank) sending unit


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#1 J-Grams

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Posted 18 September 2017 - 09:01 AM

Howdy folks,

 Just pulled off the sending unit so I can drop off my tank for an acid dip and it is rough as all get up. So I need to get a new one. Anybody have any leads on where to find one or one that might work in it's place? I haven't had any luck finding that part online.

 

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#2 Draker

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Posted 18 September 2017 - 09:03 AM

I mean it looks rough.. but if you soak it in vinegar it might clean up enough to actually function.


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#3 J-Grams

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Posted 18 September 2017 - 09:09 AM

I mean it looks rough.. but if you soak it in vinegar it might clean up enough to actually function.

That might have to be the backup plan!



#4 Stoffregen Motorsports

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Posted 18 September 2017 - 09:55 AM

Datsun 520 or 521? Just a guess.

 

I bet that one could be cleaned and used. The only thing that would be too hard to fix would be if the contact strip was worn to the bone.



#5 wayno

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Posted 18 September 2017 - 04:25 PM

That is a 320 sender(positive ground), and you need to save it, do not force the arm till you have removed the cover and lubed inside of it, be very careful and do not break it, there are very fine wires inside that cover, do not even touch them, just put some WD40 or PB Blaster in there and let it sit overnight, I repeat do not touch the wires inside that cover, they are very old and could just crumble.

Since the truck is negative ground now you might be able to use a sender from a 520/521, but I would not count on the gauge in the instrument cluster working with a different sender, you may have to use a aftermarket fuel gauge.

I tried to use a 521 tank in my L320 I have right now and I could not get the stock gauge to work no matter how I wired it, so I put the stock 320 tank back in it in the bed, as I have no room to mount the tank in the stock position as the truck has been made into a kingcab with a short box.

That was my first 320 truck I ever owned that you have there, it was also my first engine/5spd conversion that didn't bolt in, I really didn't know what I was doing back then, I was making it up as I went, it was a fun truck to drive before that kid hit me head on, front end was very lose when I owned it, likely it still is lose, I never drove it faster than 60mph after I went very fast once.

I put 437 gears in the rear end and Dan Hart sold me them dual SUs, they ran perfect when I had it.


 

 


#6 Stoffregen Motorsports

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Posted 19 September 2017 - 07:21 AM

I don't think the sending unit cares what the polarity is. The gauges may have a problem, but the sender is just a simple potentiometer.



#7 wayno

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Posted 19 September 2017 - 09:29 AM

I don't think the sending unit cares what the polarity is. The gauges may have a problem, but the sender is just a simple potentiometer.

 

Well I spent a couple hours trying to get a 521 tank to work on my positive ground L320 and I could not get it to work.

I Actually I tried using the sender/sensor by itself also without the tank, no matter how I wired it it would not work, I think it has something to do with how it is wired, ground being dedicated like say a matchbox distributor.

I tried that also, I could not make a Matchbox distributor work positive ground and I even tried on the bench, but I was able to make a MG distributor work as positive ground with a Crane ignition in it(optical) and it works great.

I can make a positive ground 320 tank/fuel gauges work wired negative ground without changing anything except the battery cables as I have 2 320s wired negative ground and the fuel gauge works, actually both were already converted over before I bought them but didn't have functioning fuel gauges, I had to pull the senders/sensors out and free them up and install a new float in one(NL320), but both work fine as negative ground.


 

 


#8 Stoffregen Motorsports

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Posted 19 September 2017 - 09:54 AM

I think there must have been some sort of problem during your testing.

 

In most cases, the fuel level sending unit simply adjusts the resistance to ground.

 

I have been known to be wrong, but this seems pretty straightforward to me.



#9 datzenmike

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Posted 19 September 2017 - 11:35 AM

It's a sensor more than a sender. It grounds the gauge to produce a reading. Usually (521/620/720) 10 ohms or less is FULL 80 ohms or more is EMPTY. I don't know if the 320 uses the same resistance readings.


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#10 wayno

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Posted 19 September 2017 - 12:10 PM

OK, I went out and did it over again, my L320 truck is positive ground, I didn't change it to see if it would work negative ground, too much work, I used 4 different senders(720/521/210-310/320) of which none were connected to the tank, I used 3 wires, one to the isolated post on the sender, one to the connection on the sensor housing, and one to a screw that mounts the sensor to the tank.

If I leave the wire on the screw that mounts the sender on the tank and switch the other 2 wires it shorts out the signal and the gauge doesn't move, it just pegs on empty. 

So the results are that all the senders work(make the gauge move) when wired in the stock configuration, the 720, 521, and 210/310 all show full when the float is in the empty position and show empty when the float is in the full position, the two 320 senders I have both show properly, empty float position is empty, full float position is full.

I do not recall what happened a year ago when I tried using the 521 tank, maybe I just didn't want it showing full when it was empty, and since my 320 sender was good I used the 320 tank and the gauge works properly.

So just to see I went out and pulled the sender wires off the NL320 which is negative ground and got the exact same results as above, empty is full and full is empty when using anything other than a 320 sender.

Now I don't know if the fuel gauge can be re-wired or not, I suppose one could try(not me), I believe it would be easier to just restore the gauge face and reverse the "E" and "F".

So far I have not tried to get the stock water/coolant temp gauge to work on the NL320 wired as negative ground, Mike installed and wired in an aftermarket temp gauge and that works for me.


 

 


#11 Charlie69

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Posted 19 September 2017 - 05:20 PM

Change the polarity to negative ground and the 521, 620, 720 senders will most likely read correct on the 320 gauge.



#12 wayno

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Posted 19 September 2017 - 05:46 PM

Change the polarity to negative ground and the 521, 620, 720 senders will most likely read correct on the 320 gauge.

 

I did that Charlie, my NL320 that Mike sold me is negative ground with an alternator.

I tested it with all senders/sensors(210/310 and 320) and only the 320 sender/sensor worked correctly(float down-empty) on the NL320, I used the 210/310 sender/sensor because it almost looks new and moves the needle in the gauge smoothly like the 720 also did, the 521 was a little jumpy. 


 

 


#13 DanielC

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Posted 19 September 2017 - 07:08 PM

Fuel gauge senders can be made with full at low resistance, or full at high resistance.  Fuel gauge senders can also have different total resistance.



#14 thisismatt

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Posted 19 September 2017 - 09:22 PM

The polarity does not matter to a resistor (potentiometer). What wayno is describing simply means the senders are wired and mechanically configured in the opposite way. On one the potentiometer is fully shorted to ground at the empty position and the other at the maximum resistance of the wire cool at the empty position. The float wire could be bent the opposite direction to fix that issue
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#15 wayno

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Posted 19 September 2017 - 09:44 PM

It might be possible to do that to a 521 sender/sensor as the arm comes out the side, and the 521 unit is adjustable 360 degrees so it can be turned around once bent so it doesn't hit the baffle in the tank.

I still think he could likely save the sender/sensor he has, the one in my NL320 tank was frozen solid and the float had a giant hole in it with several other holes, I did exactly as I suggested in my first post in this thread, I took the top cover off the sender/sensor, sprayed PB Blaster in there and on the outside and went to bed, the next day I sprayed it some more as it had all drained out or evaporated, then I grabbed the arm and slowly wiggled it til it broke loose, then I just helped it move farther and farther till it was loose and had full movement, I was very careful with it as these senders/sensors don't come along very often, I have only seen one on ebay ever. 

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#16 Stoffregen Motorsports

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Posted 20 September 2017 - 08:00 AM

So the bottom line here is, any sender should work as long as the ohm range is similar and that the range reads in the right direction. And even that can be changed with a bit of ingenuity.

 

Polarity should not matter.



#17 stevecar

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Posted 20 September 2017 - 09:32 AM

Polarity does not matter. It is the fuel gauge that needs this type of sender.

The base with the rheostat is the same as the Datsun Roadster 1500, but the arm is bent differently.

This sender works backwards from the later Roadsters, which also mount differently. I don't know about the later trucks.



#18 wayno

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Posted 20 September 2017 - 02:23 PM

Polarity does not matter. It is the fuel gauge that needs this type of sender.

The base with the rheostat is the same as the Datsun Roadster 1500, but the arm is bent differently.

This sender works backwards from the later Roadsters, which also mount differently. I don't know about the later trucks.

 

Welcome Steve  :thumbup:


 

 


#19 J-Grams

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Posted 20 September 2017 - 08:44 PM

Thanks for all the responses folks! So I think I'm going to try and repair this one I have for now. Once I pulled off the cover it actually looked pretty good. The arm is very damaged by rust. I'm going to do a thorough cleaning and see what's left of it. I don't have high hopes as it was practically crumbling apart in my hands. Might have to replace that and I definitely need a new float. I think the remnants of the float was what I heard shaking around in the tank.



#20 wayno

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Posted 20 September 2017 - 10:25 PM

That thing sat to long at that shop(over 10 years), back then I was daily driving it before the kid hit me head on, so I got it derivable again and then sold it because I could not buy a decent grill for it to save my life, the grills I found cost more than I paid for the truck, so I just gave up, I was using pump gas in it, I didn't know any better back then.

Now anything that isn't a daily driver I own with a metal tank gets non-ethanol fuel so that shit don't happen. 

 

So I did a little searching and found this, it may work for you although it is for a 1965-67 Roadster, I have one like this one but the gauge works backwards like the 521/720 senders, but a new one the arm may be bendable, or even reversible, it appears this sender will bolt right into the 320 tank, this stuff is not cheap. 

http://www.datsunroa...AGES/250-07.htm

250-07.jpg

Part number 172-09 might also work on that site and it is for a 1965 1500 which Steve mentioned above, but it has no photo, he mentioned that it may work like the 320 gauge, here is the page in the link below.

http://www.datsunroa...RIES/gauges.htm

I would call them and ask questions, ask lots of questions, if these senders will work in the 320s that would be awesome.