Gt fuel sending unit

[BDD]

My gas gauge stopped reading a while ago. It always reads empty. With the key turned to "on", when I remove the wire from the gas tank sending unit and ground it, the gauge reads full. With it removed, or on the unit, the gauge reads empty. Apparently the gauge itself works.

The sending unit is intact in the cylinder. When I tip the cylinder, the float moves freely from end to end but the gas gauge won't budge. When I removed the mechanism from the cylinder the wires were intact and where soldered at the upper ends. The solder looks a bit gray. The wires 'thread' through the wire with a contact on each side of each wire. The float is black plastic. The unit is a VDO, made in Germany.

1) Whazzup? How do I fix it?

2) Is there a certain way the mechanism has to be aligned with the tube when I reassemble it? I was very careful reassembling but want to know.

3) When putting on my new cork gasket and replacing the sending unit, 4 bolts went in through the gasket and threaded to the holes in the tank. The last bolt wouldn't go through the hole in the gasket or start threading. I backed out the other bolts to make sure the sending unit wasn't tilted and preventing the last bolt from threading. How should the gasket be aligned? I notice that there is a round notch at one area on the inside diameter but couldn't feel a notch for it to align with.

4) I could have titled this "Wazzup?" to make it easier for others to search for but didn't. I suppose, in a way, that is the main subject though. Whazzup?

[cfrantz]

Get a VOM meter (volt-ohm-meter) and measure the resistance on the sending unit to see if it is working. You can get a cheap VOM meter from Harbor Freight on sale for as little as $3. Get some contact cleaner (not the eye type) from the auto parts store and spray the wire and contacts down. The meter can also be used to find out where the problem is.

[DESTEC]

corrosion under the rivet holding the male terminal lug to the sender is seen as an 'open' hence your reading stays the same wire on; wire of the sender.

It is difficult to reestablish a good electrical connection without drilling out the old rivet, cleaning everything with 400 grt and going back with screw and nut.

Restringing that 'bow' is no east task. Try first wiggling the male terminal lug a lot (I though spraying gold chloride on the connections might help but it costs too much.) I fixed one onetime by taking a small (new, clean, sharp) jeweler's file: I wedged it into the gap on the underside and broke the tip off (1/16") off and left it there. hmmm

[DESTEC]

I created this cal curve to develop my own digital gas gauge.
Just FYI, and practical too, you can determine how much gas you have if your gauge is broke by following this diagram

[DESTEC]

.pdf attached

[BDD]

I already tried moving around the brass spade lug and brushed it and the female connector with a brass wire brush last night. I wonder if the contact cleaner might be able to work its way under the rivet? Hopefully it's not corrosive on the wire. Any thoughts on that? That is VERY fine gauge wire and I do not want to damage it.

I've got a multi-meter. Since it all looks intact its probably corrosion at the rivet.

I do see a lot of oily gunk (the technical term) that settles in the depression on the tank that the sending unit sits in. That can work its way under the rivet and insulate it. This might have been from fuel vapors from the non-existent (before I replaced them) vent lines and whatever else might have leaked through the old, brittle plastic gasket that I just replaced.

I have some very small diameter piano wire, some of it might be stainless steel. If all else fails, maybe a short length of that could be forced under the rivet and form an electrical contact.

I wonder if you could clean the top of the rivet, away from those fine wires, use some flux and melt some solder into it. Maybe that could resestablish a current path from the rivet to the top of the sending unit.

[sawdust]

Originally Posted by BDD I wonder if you could clean the top of the rivet, away from those fine wires, use some flux and melt some solder into it. Maybe that could resestablish a current path from the rivet to the top of the sending unit.

I wouldn't do that. You just might short the signal wire to ground.

You might try soaking it in carb cleaner for a couple hours.

If that don't work you don't have to many options.
1. drill out the pop rivet
2. drill and tap a new screw hole and solder the spring to it.

[BDD]

Is there a spring?
Mine was a linear arrangement that had a very fine wire on each side that contacts on each side of the float made contact with and acted as wire guides. I was thinking that the float just went up and down varying the resistance with no spring involved.

[DESTEC]

BDD, If you want and if you cover the freight both ways i'll fix it for you for free (if the Ni-Chrome wire is still in tact.) If its doable, I can do it.

send to DESTEC Engineering, Atten JJ Wheatley POB 2537 Stuart, FL 34995

[BDD]

Sir, you are a gentleman and a scholar.

I took another look tonight and the nichrome wires are intact. When I take the resistance between the terminal lug, from wire to wire near the top or from lug to opposite wire at the top I get a low resistance with the float high and a large resistance, 80 or 90 Ohms, when the float is low. I don't get any reading from lug to center rivet or case. I do get the proper resistances measured from lug to the copper disc at the top but there is corrosion or fuel build up that tends to prevent electrical contact. When I put it back in the tube and connect the wire the tank still reads empty as I slide the float from end to end.

I suppose that copper disc isn't being grounded against the metal top.

[sawdust]

Originally Posted by BDD I suppose that copper disc isn't being grounded against the metal top.

I think you finally got it. That copper disc is the spring tensioner.

[George]

I drilled a small hole through the metal top and copper disc and used a small brass bolt and nut to make a new ground.

[BDD]

Just got my sending unit back from Destec. Put it in and turned the key and it works perfectly. As I thought from taking it apart and testing it, slight corrosion had made it so the wires weren't grounded. He improved the grounding and I think that it it will probably keep working for quite a while with the repair he did. If you don't want to mess with yours or risk damaging those very fine wires or the electrode wire guides you might see if you can work something out with him.

[markandson]

One extra caution about fuel senders. I rebuilt mine and it is working perfectly, but when I put it in the car it did not work. I cleaned and coated my gas tank inside and out with proper sealers. I did too good of a job . and it caused me to lose ground because the Por 15 on the outside of the tank acted like an insulator. To fix the problem I ran a ground wire from one of the sender screws to a good known ground point in the rear of the car, now my sender works perfectly.

[traytodd]

Gil has the sender wire to repair tank gauges. I fixed mine but after a couple of practice runs. Getting the tension right on the wire without breaking it is tricky. I replaced the rivet with a brass screw and nut and peaned the screw to make sure it did not come loose. Works fine now.