We big car guys have trouble finding fuel sending units, or at least I do. Last week I got one from Ebay which turned out to be from a 65-66 Cutlass. Which are different.

I still had my original '66 98 fuel sending unit, so I wanted to see if I could use the NOS cutlass electrical parts in my big car part. Turns out you can, but I'm not sure how strong it will be...

Here's what big car vs. A body sending units look like side by side. Note that these are both for Non-AC cars, if they were AC units, they'd have a fuel return line.

Mid 60's Big car vs. Cutlass non-AC fuel sending units. Big car unit is in front

I just cannibalized the Cutlass unit for a new ground wire. I put a new filter sock on too. It was kind of a pain to cut the old one off. To secure the new one, you have to bend some ears around it to ensure mechanical retention. But it worked.

Here's how to open the resistance wire housing. Standard GM bent-ears closure

With some small pliers you can open this housing by bending the three ears. Look out for the spring inside which loves to jump away!

Here's what the inside of your fuel sending unit looks like:

Once you open it, here's the contact point and resistance wire inside which provides varying voltage to your fuel gauge based on float position

Check out 50+ years of wear on my original resistance wire! Well built. This part had >300,000 miles on it when pulled. Good quality.

Well built, simple. GM knew what to do.

If you go to repair yours, here's a shot of the thickness of an unused fuel sending unit contact point for reference:

GM fuel sending unit contact point thickness. You want this to touch the resistance wire lightly, not wear it down every time you fuel up.

So I just soldered a drop onto my original contact point and swapped in the new Cutlass variable resistance wire housing. But to do that I had to disconnect and reconnect my much longer resistance thick wire to the "new" wire housing.

The big question in my mind is whether I've built a robust part. Originally GM swaged the big thick wire onto the resistance housing. I couldn't do that so I precisely bent the black wire to force it against its contact pin, then put a fairly good dollop of solder on top. After doing that I disassembled the housing once or twice and it's holding.


GM origninally swaged metal around this pin for a strong connection

Do you think the solder will hold up almost as well?

Do you guys think this will hold long term? I'd hate to get this in the tank and have it only last a few months.... Opinions?

I checked the Ohms range for both sending units. My unrestored unit wire ran from 20 - 119 ohms resistance, the restored unit runs from 16.5 ohms to about 119 as well. Electrically I think I'm in business.

But I wonder if it will endure...

Cheers
Chris

Hope this is fun for you all.

 

Great procedure/tutorial. It may last for years. Thanks.