Sending unit test

A

adam metzger

New member
Oct 12, 2016
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Finally got the time to drop the tanks on the coach! I got the sending units out and tested them. I get a proper 3-93 ohms reading on one. On the
other, I cannot get a reading when I put the probe to the positive terminal, but do get a reading if I probe under the plate, where the wire attaches
to the terminal on the bottom. The reading isn't 3-93, but 90-ish to 180 ish, so still 90 ohms. Is this a problem? If one were to want to replace
the terminal, what would be the best way to do so? I know I there's only the need for one working unit, but if it's not too much trouble, I'd rather
have two working senders.

I'll have more questions coming, as I get these tanks cleaned up and re installed.

Thanks everyone.
--
1976 Palm Beach
Austin, TX
 
It sounds like the rivet which connects the wire and terminal is loose or corroded. Carefully drill it out and replace it with a suitably sized brass
bolt, nut, and star washer and it should make constact properly.

--johnny
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"The road goes on forever, and the party never ends" --Robert Earl Keen
 
Read here
http://bdub.net/gmcmotorhome.info/Fuel.html

Buy new stainless ones😀

On Sat, Dec 31, 2016 at 6:18 AM Johnny Bridges via Gmclist <

> It sounds like the rivet which connects the wire and terminal is loose or
> corroded. Carefully drill it out and replace it with a suitably sized brass
>
> bolt, nut, and star washer and it should make constact properly.
>
>
>
> --johnny
>
> --
>
> '76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and
> add - ons.
>
> Braselton, Ga.
>
> "The road goes on forever, and the party never ends" --Robert Earl Keen
>
>
>
> _______________________________________________
>
> GMCnet mailing list
>
> Unsubscribe or Change List Options:
>
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
 
The sensor specs are 0-90 ohms. I believe the gauge reads Full when the sensor is at 90 ohms. Therefore with your 90-180 ohm sensor, the gauge will
never read below Full.

There must be a faulty connection in the sensor which is adding another 90 ohms in series. The connection through the mounting plate is just a stud
and should be 0 (zero) resistance from the top to bottom. If I remember, there is just a spring clip holding the conductor from the sensor to the
through-plate stud which could be oxidized causing an open circuit. Using your ohm-meter, check the connections and find where you lose connection
through the plate and where that additional 90 ohms is coming from.

Having both senders working is important in my opinion. Its amazing how much fuel will transfer from the rear tank to the front tank when going
downhill and braking due to the position of the filling ports. I've seen my rear tank read near empty while my front was well over 3/4 while coming
down the long hill into Watkins Glen NY. I'd spend some time getting the faulty tank sensor back working.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Adam,

This is not a suggestion.
I had the same issue, but with both senders (one after the other..)
The problem is that the connections are not at all corrosion resistant. In electronic builds, they often talk of a gas tight contact and there is a
real good reason. I tried tightening the connections. That yielded poor results.
I tried to solder a piece of wire from the sending unit to the inside of the terminal and that only served to make the connection to the nichrome
winding unreliable.
It also loosened the connection to the outside top terminal and that required that I solder the push-on to the rivet. That damaged the insulators. I
made new ones and used screws.

I finally bought new sending units and modified the pick-ups and the new sending units so they could all work together. This was not a simple job and
I will never write it up as a program. This was just a part of why I am so well versed in how to get tanks down and back up.....

This is the suggestion. Contact the place that rebuilds sending units. Box up the two sending units. Tell the nice people "Make them all better and
send them back".

My way was clearly not efficient.

Matt
--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
I decided that if I was going to send them
In for repair, I might as well try to fix them. If I screwed them up, well I'd be sending them
In anyway...

I was getting really inconsistent readings on both senders. They would range correctly, then jump all over the place.

I drilled out the positive post like Johnny mentioned. The grommets were in varied conditions. One split right away, and one cracked but not to the
middle. The two on the underside survived.

I removed the pin, and contact strap from the baseplate. Cleaned the strap with a rotary tool brush, used rubber washers and a brass screw and nut
and re assembled. Tested again, and more consistent range than before, but would still bounce around on one and was all over the place on the other.
Jumping from 10 to 7000 with everything in between.

I decided I was gonna dive in and sink or swim. I bent the tab on the flat side of the housing, then slid the housing off. I figured it would be
better to break one tab instead of three. This proved to be a good decision.

Inside I found the potentiometer windings and the contact point both on pretty dirty shape.

I cleaned both with contact cleaner, let dry, then used a trick I found while searching for info on this topic.

Apparently a pencil eraser is a great cleaner to remove the buildup on the contact point. Sure enough, it gets it shiny as a new penny. I cut the
eraser off the pencil so I could get it into the inside of the case, and gently cleaned the windings.

on the unit that was acting up, I noticed that the windings were not centered on the board inside that keeps it seperate from the casing. In fact, it
was so far off the board, it was actually grounding. I adjusted the board, cleaned and re-assembled the unit.

I did break the tab on one pressing it back down. The other seems okay. I imagine a touch of JB weld will do just fine.

I tested each unit, and am getting a consistent range of 10-100 on both senders with no jumping around.

I took pics, and will edit this post with pics tomorrow when I have access to a computer.

--
1976 Palm Beach
Austin, TX
 
I remember using pencil erasers to clean up contacts on my afx slot cars as
a kid. Those things were cool.

Sully
77 eleganza 2
Seattle

> I decided that if I was going to send them
>
> In for repair, I might as well try to fix them. If I screwed them up, well
> I'd be sending them
>
> In anyway...
>
>
>
> I was getting really inconsistent readings on both senders. They would
> range correctly, then jump all over the place.
>
>
>
> I drilled out the positive post like Johnny mentioned. The grommets were
> in varied conditions. One split right away, and one cracked but not to the
>
> middle. The two on the underside survived.
>
>
>
> I removed the pin, and contact strap from the baseplate. Cleaned the
> strap with a rotary tool brush, used rubber washers and a brass screw and
> nut
>
> and re assembled. Tested again, and more consistent range than before,
> but would still bounce around on one and was all over the place on the
> other.
>
> Jumping from 10 to 7000 with everything in between.
>
>
>
> I decided I was gonna dive in and sink or swim. I bent the tab on the flat
> side of the housing, then slid the housing off. I figured it would be
>
> better to break one tab instead of three. This proved to be a good
> decision.
>
>
>
> Inside I found the potentiometer windings and the contact point both on
> pretty dirty shape.
>
>
>
> I cleaned both with contact cleaner, let dry, then used a trick I found
> while searching for info on this topic.
>
>
>
> Apparently a pencil eraser is a great cleaner to remove the buildup on the
> contact point. Sure enough, it gets it shiny as a new penny. I cut the
>
> eraser off the pencil so I could get it into the inside of the case, and
> gently cleaned the windings.
>
>
>
> on the unit that was acting up, I noticed that the windings were not
> centered on the board inside that keeps it seperate from the casing. In
> fact, it
>
> was so far off the board, it was actually grounding. I adjusted the board,
> cleaned and re-assembled the unit.
>
>
>
> I did break the tab on one pressing it back down. The other seems okay.
> I imagine a touch of JB weld will do just fine.
>
>
>
> I tested each unit, and am getting a consistent range of 10-100 on both
> senders with no jumping around.
>
>
>
> I took pics, and will edit this post with pics tomorrow when I have access
> to a computer.
>
>
>
>
>
>
>
>
>
>
>
> --
>
> 1976 Palm Beach
>
> Austin, TX
>
>
>
> _______________________________________________
>
> GMCnet mailing list
>
> Unsubscribe or Change List Options:
>
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
 
Adam,

You've done as I did a couple of times 'way back. The technique works well
but I have one caution: The "rubber washers" you used to insulate the
terminals will most likely not survive the ethanol--laced gasoline for very
long. Then you'll have fuel leaking around the contacts. I encourage you
to find some nylon or other ethanol-resistant washers to replace the rubber
(if they're faucet washers, they almost certainly will not hold up). No
use having to drop the tanks again just for that little problem -- been
there, done that.

Ken H.

> I decided that if I was going to send them
> In for repair, I might as well try to fix them. If I screwed them up, well
> I'd be sending them
> In anyway...
>
...

> Cleaned the strap with a rotary tool brush, used rubber washers and a
> brass screw and nut
> and re assembled....
 
Hi Ken- the bottom washers that are on the senders survived. Do you think the washers/insulators on the top of the senders need to be fuel proof
too? I can't think of a reason this deal needs to be perfectly air/fuel tight. Thoughts? I got nylon washers and spacers too. I actually just
grabbed a bunch of different stuff to see what would work. Thanks for the heads up.

--
1976 Palm Beach
Austin, TX
 
Adam,

I don't think the bottom washers alone will seal the connection. If they
would, why wouldn't steel washers do on top? I DO think the senders need
to be fuel tight -- otherwise they'll leak when the tank's full. I just
don't see any reason to not do the very best possible while at it to avoid
difficult work later.

Ken H.

> Hi Ken- the bottom washers that are on the senders survived. Do you
> think the washers/insulators on the top of the senders need to be fuel proof
> too? I can't think of a reason this deal needs to be perfectly air/fuel
> tight. Thoughts? I got nylon washers and spacers too. I actually just
> grabbed a bunch of different stuff to see what would work. Thanks for the
> heads up.
>
>
 
Hi Ken-

I realized that my statement may come across as me seeming lazy instead of actually curious.

I agree, and will find a way to seal it. both of my top rubber isolators are hard, and the bottom washers are soft. I was thinking that maybe it was
different material, not necessarily for sealing the hole super tight as much as isolating the contacts. I'll concede to much more experienced minds.

I've been toying with the idea of using a fuel resistant gasket maker, and making gaskets. how hard could it be, right? :p

--
1976 Palm Beach
Austin, TX
 
> Hi Ken-
>
> I realized that my statement may come across as me seeming lazy instead of actually curious.
>
> I agree, and will find a way to seal it. both of my top rubber isolators are hard, and the bottom washers are soft. I was thinking that maybe it
> was different material, not necessarily for sealing the hole super tight as much as isolating the contacts. I'll concede to much more experienced
> minds.
>
> I've been toying with the idea of using a fuel resistant gasket maker, and making gaskets. how hard could it be, right? :p

Adam,

If it goes wrong, your have two issues:
Shorting the signal will read full or over.
The possibility of an ark in the fuel environment.....

Do you have a friend that owns a lathe??
Buy him a piece of nylon rod stock. He can make washers/spacers with the step to hold the center.
Or, get a pair of nylon washers and a tiny O-ring to crush between them.

The second is what I did for a repair when I was away from my lathe. Not in my coach fuel tank, and I am going to make the right parts some day.

Matt

--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
When I did my in-tank fuel pump installation I was able to find nylon stepped waters and and nylon regular washers in the parts boxes at my local ACE hardware store.
I had to drill out the regular washers to fit over the stepped washers on the outside of the sender.
Much easier than having to have some machined.

Emery Stora
77 Kingsley
Frederick, CO

>

>> Hi Ken-
>>
>> I realized that my statement may come across as me seeming lazy instead of actually curious.
>>
>> I agree, and will find a way to seal it. both of my top rubber isolators are hard, and the bottom washers are soft. I was thinking that maybe it
>> was different material, not necessarily for sealing the hole super tight as much as isolating the contacts. I'll concede to much more experienced
>> minds.
>>
>> I've been toying with the idea of using a fuel resistant gasket maker, and making gaskets. how hard could it be, right? :p
>
> Adam,
>
> If it goes wrong, your have two issues:
> Shorting the signal will read full or over.
> The possibility of an ark in the fuel environment.....
>
> Do you have a friend that owns a lathe??
> Buy him a piece of nylon rod stock. He can make washers/spacers with the step to hold the center.
> Or, get a pair of nylon washers and a tiny O-ring to crush between them.
>
> The second is what I did for a repair when I was away from my lathe. Not in my coach fuel tank, and I am going to make the right parts some day.
>
> Matt
>
>
> --
> Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
 
Digikey has shouldered insulating washers. They may not be the least cost (only talking about 20 cents) but they ship the same day and I get my order
next day here in Canada for only $8.00Cdn and no minimum order. So shipping should be cheaper and just as fast in the USA.

Shouldered insulating washer page:
http://www.digikey.ca/products/en?FV=fff40020,fff803fd&k=washer

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Ken, can you tell me what you used to seal and isolate the contacts? I'm considering buying a sheet of Viton or Karropak gasket material. A punch to
make the washer and a needle through the middle should seal it fine.

The top washer is 1/8 thick. About the same thickness as fuel line. Cutting a piece in a small square would more than cover it, and the concave side
down would add some tension, adding to the seal. Why would that not work?
--
1976 Palm Beach
Austin, TX
 
Adam,

After the failure of my earlier repair, I replaced the entire pickup
assembles with new SS ones fromeBay:
http://www.gmcmhphotos.com/photos/g6842-fuel-tank-sender-replacement.html

So, in view of my failure, I'm reluctant to recommend any particular
repair. :-)

Good luck!

Ken H.

> Ken, can you tell me what you used to seal and isolate the contacts? I'm
> considering buying a sheet of Viton or Karropak gasket material. A punch to
> make the washer and a needle through the middle should seal it fine.
>
> The top washer is 1/8 thick. About the same thickness as fuel line.
> Cutting a piece in a small square would more than cover it, and the concave
> side
> down would add some tension, adding to the seal. Why would that not work?
> --
>
 
Ken:

The best “repair” is a “replace”.

Stainless, too!

Thanks for the tip.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
1-Ton, Sullybilt Bags, Reaction Arms, 3.70 LSD, Manny Transmission, EV-6010

“The Aluminum and Fiberglass Mistress"

>
> Adam,
>
> After the failure of my earlier repair, I replaced the entire pickup
> assembles with new SS ones fromeBay:
> http://www.gmcmhphotos.com/photos/g6842-fuel-tank-sender-replacement.html
>
> So, in view of my failure, I'm reluctant to recommend any particular
> repair. :-)
>
> Good luck!
>
> Ken H.
>
>

>
>> Ken, can you tell me what you used to seal and isolate the contacts? I'm
>> considering buying a sheet of Viton or Karropak gasket material. A punch to
>> make the washer and a needle through the middle should seal it fine.
>>
>> The top washer is 1/8 thick. About the same thickness as fuel line.
>> Cutting a piece in a small square would more than cover it, and the concave
>> side
>> down would add some tension, adding to the seal. Why would that not work?
>> --
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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