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mr928

gas gauge / sender issues

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I've read that a common problem is the voltage regualtor on the back but how do you test it? I've cleaned the contacts and taken it apart and I see no obvious problem. I removed the sender and verified that it works at all different levels but I'm not sure what the resistnace should be. My gauge shows full when the tank is full but will only drop to about 1/2 way even when almost empty. When I turn the key off the needle does drop. I've tried to adjust the gauge from the rear but to no avail. Does this sound like a bad gauge?

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Cherck the wire to the sender, they are on a ground system and it could be slightly grounded as to not let the needle drop all the way. Atleast not till the power is off. Try dissconnecting the sender wire(at guage) and see if it drops all the way.

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Cherck the wire to the sender, they are on a ground system and it could be slightly grounded as to not let the needle drop all the way. Atleast not till the power is off. Try dissconnecting the sender wire(at guage) and see if it drops all the way.

 

I did pull the wire off the sender and it does drop all the way down.

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If the temp gauge is unaffected then it's not the voltage regulator as it feeds both. Both gauges have a steady supply regulated at about 8 volts to prevent varying readings due to varying battery charge when haveing lights and different accessories on at idle. Power flows through the gauge, and through the varying resistance in either sender and to ground.

 

The resistance on the sender is about...

10 ohms (or less) full

25 ohms @ 3/4

40 ohms @ 1/2

56 ohms @ 1/4

80 ohms (or more) at empty.

 

If you removed the sender and checked it moves the full travel then I would say that either it sticks at half when installed or does not have room to swing fully and is hitting something when installed.

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So like mike says, the sender either isnt moving all the way down or the guage is bad.

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If the temp gauge is unaffected then it's not the voltage regulator as it feeds both. Both gauges have a steady supply regulated at about 8 volts to prevent varying readings due to varying battery charge when haveing lights and different accessories on at idle.

You always have great information!

Would this information be the same for my '74 620?

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If it's only dropping half way that's usually a dead sign the regulator is bad. But it would affect BOTH the temperature gauge and fuel gauge equally. Of course if the temp gauge isn't working (common) then you won't notice it.

 

When the regulator goes bad it just goes bad. You won't see anything wrong with it unless it went bad in a spectacular fashion.

 

I will mention that at one time I had that problem happen when the MAIN voltage regulator (the one for the charging circuit) went bad. Made both gauges read double. However, this was a 510 which I don't believe has the gauge cluster regulator. But it's something to think about.

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So like mike says, the sender either isnt moving all the way down or the guage is bad.

 

Dave he says it reads full when tank is full and drops to empty when the key off so I think it's safe to assume the gauge is free to move and is functioning, just getting a 1/2 full signal and displaying it. I suppose the only totally positive way to test is remove the sender and connect it and swing the float through it's full movement.

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Was thinkin maby messed up wires in the guage could make it have a minimum reading when powered up?

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Sometimes 40 year old equipment just gives up, I used to fill my 521 tank and it would show full, but now after 15+ years of use by me, this year it won't go to the top anymore, but my temp gauge works fine, so the tank sender is giving up more than likely.

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Dave he says it reads full when tank is full and drops to empty when the key off so I think it's safe to assume the gauge is free to move and is functioning, just getting a 1/2 full signal and displaying it. I suppose the only totally positive way to test is remove the sender and connect it and swing the float through it's full movement.

This is what I would do.

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Sometimes 40 year old equipment just gives up, I used to fill my 521 tank and it would show full, but now after 15+ years of use by me, this year it won't go to the top anymore, but my temp gauge works fine, so the tank sender is giving up more than likely.

This sounds like the oposite symptoms than the original post to me.

I have had old floats in the sending unit develop small leaks. In those cases; when the tank is filled all the time, the float gathers fuel and doesn't float as high. If the tank sits empty for a long period the float drains, and the gauge reads correctly again. If this sounds like what you're seeing ... it might just be a leaky float in the sending unit?

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This sounds like the oposite symptoms than the original post to me.

I have had old floats in the sending unit develop small leaks. In those cases; when the tank is filled all the time, the float gathers fuel and doesn't float as high. If the tank sits empty for a long period the float drains, and the gauge reads correctly again. If this sounds like what you're seeing ... it might just be a leaky float in the sending unit?

 

 

The point I was making is that this equipment is getting old, if it is a float sinking, it's still part of the sender.

I have another one that has the same symtoms as he has, the needle won't go below a third of a tank, but when I turn the key off, it goes to empty, but I thought it wasn't a good example, because it is a 720 tank, connected to a 521 gauge/cluster, my water temp works fine, but the fuel gauge is not reading correctly, and I should mention that the fuel gauge needle goes way past the full mark and stays there for quite a while.

I have another 520 set up exactly the same way, 520 gauge/cluster, 720 tank, and it seems to work properly, although I have not put any street miles on the rig yet, as it is half bare metal, so I don't want it getting wet yet.

I have a question for mr928, has the tank ever been hit/bottomed out, where the bottom of the tank has been pushed up, that will also cause the same symtoms.

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If the temp gauge is unaffected then it's not the voltage regulator as it feeds both. Both gauges have a steady supply regulated at about 8 volts to prevent varying readings due to varying battery charge when haveing lights and different accessories on at idle. Power flows through the gauge, and through the varying resistance in either sender and to ground.

 

The resistance on the sender is about...

10 ohms (or less) full

25 ohms @ 3/4

40 ohms @ 1/2

56 ohms @ 1/4

80 ohms (or more) at empty.

 

If you removed the sender and checked it moves the full travel then I would say that either it sticks at half when installed or does not have room to swing fully and is hitting something when installed.

 

 

Thanks Mike,

I wil remove it and verify that.

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I have a question for mr928, has the tank ever been hit/bottomed out, where the bottom of the tank has been pushed up, that will also cause the same symtoms.

 

 

I see no signs of damage. I drained the tank and removed the sender. Looked inside and it looks nice and clean and nothing but gas came out when I drained it. I do not think my temp gauge work well either. It shows some movent but it's not accurate. Does anyone know a source to buy the voltage regulator on back of the gauge cluster?

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I see no signs of damage. I drained the tank and removed the sender. Looked inside and it looks nice and clean and nothing but gas came out when I drained it. I do not think my temp gauge work well either. It shows some movent but it's not accurate. Does anyone know a source to buy the voltage regulator on back of the gauge cluster?

 

 

If you temp gauge doesn't work properly either, then it's quite likely the power source could be the issue, wish I knew about this when I sent the last box down, there was lots of room in it.

Anything else not working properly?

Door hardware?

Throddle, e-brake cables?

How would one check the temp gauge if the power source had issues, normally one would

check the temp gauge by grounding out the wire, it should show full hot when grounded out.

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wish I knew about this when I sent the last box down, there was lots of room in it.

Anything else not working properly?

 

Yes Wayne I should have mentioned that and thanks again for everything so far. My current wish list is as follows:

 

dash volt regulator

 

steering shaft firewall seal

 

dash top

 

interior light

 

off-heat lever

 

steering wheel

 

engine compartment light

 

window crank arms (mine are both bent but working)

 

mud flaps

 

2 rust free hub caps

 

The extra parts I have available free for anyone are:

 

blinker turn assembly- column switch

 

brake cylinder shims

 

speedometer (works and is calibrated but non functioning odometer)

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Dash volt regulator (if still available) is 25020-13200 about $15

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Dash volt regulator (if still available) is 25020-13200 about $15

 

 

Thanks Mike but I believe it is NLA throught Nissan. I've tried my dealer.

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Yes Wayne I should have mentioned that and thanks again for everything so far. My current wish list is as follows:

 

dash volt regulator

 

steering shaft firewall seal

 

dash top

 

interior light

 

off-heat lever

 

steering wheel

 

engine compartment light

 

window crank arms (mine are both bent but working)

 

mud flaps

 

2 rust free hub caps

 

The extra parts I have available free for anyone are:

 

blinker turn assembly- column switch

 

brake cylinder shims

 

speedometer (works and is calibrated but non functioning odometer)

 

I have the dash voltage regulator, and maybe the window cranks, i'll have to look into that tomarrow.

You will need to make your own steering shaft seal like I did here.

DSCN0207.jpg

You will need to get a 520 dash top, or make a cover for your dash.

DSCN0677.jpg

DSCN0678.jpg

DSCN0680.jpg

I have never seen a complete engine compartment light, although I will look for you, you could probably make one more reliable than I could find.

Your on your own on the heater knob, if I find one, it'll be mine, as I have 3 rigs and two knobs.:unsure:

Maybe your not talking about the knob, are you talking about the lever on the bottom of the dash?

What kind of hubcaps do you have?

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Thanks Mike but I believe it is NLA throught Nissan. I've tried my dealer.

I have one new in the box if you want. PM me

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Thanks for the pictures Wayne. I will make my own stering shaft seal like you did and I will recover my own dash. I'm just hoping to do it in a way that looks a lot like stock. I'm really trying to make this truck as close to original as possible.

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