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Commander Member

2275 Posts

Posted - 10/13/2009 :  3:50:47 PM  Show Profile  Email Poster  Reply with Quote
Update, with a photo story.

I got the fuel tank drained on the 2R6. Lots of nasty, stinky gunk and rust in there. It will have to boiled out with caustic to clean it. Anyway, I had another tank that came with the truck, so I fetched it, and removed the fuel sending unit so I could look inside. The sending unit had been sealed with some kind of resin, which was all cracked and curled, and one screw was broken off flush with the top of the sending unit base.

This tank proved to be quite clean inside with only a few tiny rusty patches, and a little loose rust and dust, which I sucked out with a vacuum cleaner. The tank hasn't held fuel in years. To remove the broken sending unit screw, I resorted to MIG welding a metal strip to the stub, and backing it out. I put a piece of metal duct tape over the other holes, so sparks and slag from the welder couldn't enter the tank. I wasn't really worried about an explosion from a tank this dry. If the tank HAD recently held fuel, I would have filled it with water nearly to the top before trying this stunt. In any case, it took about 4 or 5 go rounds with the MIG to get the screw backed out, but out it came, with no damage to the threads. I think somebody put an overly-long screw into a blind hole, which will do it every time. You can see the removed stub, welded to the metal strip in the first picture, along with the disassembled sending unit from the stinky tank. (The sending unit from the clean tank proved to be a 12 volt one, and it looks like an aftermarket replacement. It's also flaky.)

Well, the six-volt sending unit was darn near as nasty as the tank it came out of. The cork float was heavy with absorbed gunk, and checking on an ohmmeter revealed the jumpy sort of resistance-displacement curve that is characteristic of a worn-out sending unit.

You can see the hole in the tip of the bronze wiper in the above picture. It was manufactured with a raised bump stamped into it, and it's the bump that tracks along the resistance element. Eventually the bump wears through, leaving a hole that spans about 3 turns of wire on the element. As the float moves, first one edge, then the other, makes good contact with the resistance wire. The result is a gauge that "kinda-sorta" follows the level of fuel in the tank, but it will persistently jump back up a pointer-width or so as the fuel level goes down, and then resume dropping again.

Anyway, the fix was easy. First, I dipped the end of the wiper in hydrochloric acid to make it bright and shiny so it could take solder. Then I found a piece of silver solder rod in my welding kit, and ground a round point on it, and clamped it in the vise. Then I slipped the hole in the wiper over the end of the rod, so that the rounded point would be on the contact side, and propped it up so I could solder it. Once the solder had cooled, I clipped the rod off on the back side of the wiper, and dressed the front side with a fine file. Here's the finished product:

Incidentally, the metal can that houses the guts of the sender is held to the base plate by swages. Little raised studs were formed on the underside of the base plate when it was stamped. The can has 3 punched holes that fit over these studs, which were then hammered over like rivets. I ended up welding the can back to the base plate with the MIG, but if you don't want to weld, you might be able to reuse the old swages, and stake them with a pin punch, or drill them out and use actual rivets, or even epoxy the can back on there. The little "bearing" strip that holds the wiper in the can was attached by rivets, which I ground off, and replaced with tiny sheet metal screws. Here's the finished product, assembled:

Since I happened to have on hand a fuel sending unit out of an old Jeep Wagoneer fuel tank, with a hollow brass float, I elected to use it to replace the soggy, stinky cork float. I simply laid the new float back-to-back with the old one, marked both wires for a 1" overlap, and cut both wires, then laid the cut ends together at the marks and welded the two wires together with the MIG (carefully, so I didn't burn through the slender wire.) Again, there are alternative ways to do this, for those not wishing to weld.

I've posted descriptions of this process before, but I had the presence of mind to take pictures as I did it this time. Total time involved in the sending unit repair? About an hour. Yes, you can get new sending units (for some models) from the vendors, but they aren't cheap, and it will take a day or two, at least, to get one.

One curiosity I ran across: the old stinky tank I took down out of the truck has the filler neck equipped to accept a cap, with the same sort of slotted flange that is used on the filler neck itself. The replacement tank simply has an unadorned inlet pipe. Anyone have an explanation for this?

Gord Richmond, within Weasel range of the Alberta Badlands
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