How to restore fuel sending unit?

[William L.]

I had a fuel leak on my 67 coupe today when I removed the sending unit it, along with the bottom of my tank was very very rusty. Ordered a new OEM tank but nobody seems to have the correct sending unit with MADE IN USA and the large S. Any ideas on how to restore the unit? The sending unit works fine. Sandblasting and maybe a fuel proof Paint?
Thanks Bill

[Joe R.]

Re: How to restore fuel sending unit?

Hi Bill:

Are you saying that the sender unit works fine but has a leak? Do you know the location of the leak?

One place that these senders sometimes leak is at the soldered junction where the outlet pipe passes through the base plate. If that is where yours is leaking, you can probably clean the area and re-solder it.

If the base plate itself is rusted through, I don't think you should try to repair it. It's not worth taking chances where potential fuel leaks are involved.

I don't think anyone makes a reproduction with the correct markings on the base plate (see attached photo of an orignal). My initial plan for restoring mine, which had a bad potentiometer, was to buy the almost-correct reproduction from Corvette Central and splice their tank-side portion onto my original. The tubing is 3/8 inch and a 3/8 splice fitting can be purchased at a plumbing supply house or large hardware store.

I ended up buying a NOS sender with the correct markings, so I never completed my original plan. If you need a clean original base plate, contact me off line. I have a few unrestored original senders.

[Mike M.]

Re: How to restore fuel sending unit?

Hi Joe, I have a fuel sending unit that the outlet pipe is loose and turns. I was putting this on a new tank yesterday when I noticed the problem. I would think it will leak there. I would assume re-solder on the inside also if that will fix this.
Mike

[Joe R.]

Re: How to restore fuel sending unit?

Hi Mike:

The outlet pipe is soldered where it passes through the base plate, and it is also soldered to a support bracket less than 2 inches up from the plate on the tank side. Both of these joints need to be well secured to stabilize the pipe.

It is easy to dislodge one or both joints if you pull hard on the rubber hose when trying to remove it from the outlet pipe. A better method for hose removal is to split the hose with a razor blade and then use a new hose when you reinstall the sender.

I had good success re-soldering my sender using some 50-50 plumber's solder, some solder paste flux, and a mapp gas torch. The base plate has a small well around the outlet pipe that you can fill with solder to get a good, strong bond.

It takes some finesse to get the temperature just right so that the solder flows well but doesn't leak out between the pipe and the hole in the base plate. Also, the areas to be soldered need to be very clean. A wire brush on a Dremel tool works well for that.

[Mike M.]

Re: How to restore fuel sending unit?

Joe, I didn't take this car apart, so I get a surprise every once in while, either parts not there or something like this comes up. I give it try. I think I'll use silver solder it holds a little better.
Thanks Mike

[Joe R.]

Re: How to restore fuel sending unit?

Silver solder requires a lot more heat, so be careful to protect all the non-metal parts such as the potentiometer and the seals around the two connectors that penetrate the base.

I think I removed the two connectors prior to soldering the base plate. That introduces some risk that they will leak when reassembled, so be careful with that, too.

It's amazing to me that C2 senders don't leak more frequently than they do. Since the sender is on the bottom of the tank, the outlet pipe joint and both of the connector seals always have gas against them.

[Mike M.]

Re: How to restore fuel sending unit?

Joe, when you put the connectors back on did you put anything on them to help seal them so they wouldn't leak.

[Joe R.]

Re: How to restore fuel sending unit?

I did not add any sealant, but as I recall the seals on mine looked okay. I believe that different types of seals were used during the C2 years, so some may withstand aging better than others.