Gas Tank Sending Unit - 06/07/2014

Few things annoy me more than gas gauges not working on a car. I decided that since I was down for a fuel pump replacement I might as well take advantage of the situation and drain the tank to replace the sending unit. Pretty straightforward job, I've even done it a few times already!

First things first, get the oil changed. Not particularly exciting. Sure stinks of gas though...

Getting a gravity fed siphon going! Just crack the fuel pump output line to get gas flowing, then undo the source line from the tank and put it below the tank. It will drain the tank dry in no time.

Yup, we're on bucket brigade duty. The Prius needed gas, so 8.5 of the gallons went into it.

Fully drained. It took about 30 minutes to completely empty out around 14 gallons from the tank.

Time to get to work. Support the car up high to get room to work.

In 1969 they still vented these gas tanks to the atmosphere via 2 rubber tubes and coiled metal tubes attached. The filler neck has one that needs to be removed.

Remove the ground wire. Don't want it ripping or hanging up. U-bolt caged nut on the right isn't too bad, but someone sprayed undercoating all over the tank and fittings so it has required some chiseling to get off.

Remove the crusty old fuel lines. These will be replaced.

The other vent at the back of the tank. In 1970 they went to a 3 vent system that vented to a cannister above the floor in California and in 1971 all cars were vented to a cannister behind the back seat and a charcoal filter in the engine compartment. This u-bolt caged nut broke free so it required some serious effort and contorting to get it free - someone sprayed the bolt with rubberized undercoating and made it very difficult to get out. Even more so when you don't have the proper tools to make it easier.

Tank is out. This tank has a complete sheet of insulating rubber and tar paper on top of it, I don't think it's ever been out of the car. No build sheet though, so more evidence to dispute the "ALL cars have build sheets on their gas tanks" theory.

Trunk floor is in great shape. That body plug being missing needs to be fixed as it's allowed all the dirt and junk in the trunk to get on top of the gas tank for years.

Tar paper removed, tons of sand exposed. Once the sand is removed you get shiny metal and even still have the US Steel ink stamps on top from the factory.

Old sending unit removed. Filter sock has disintegrated many moons ago. It isn't obvious why it doesn't work, multimeter reveals it's not a ground wiring issue, so it's probably in the potentiometer arm movement.

Other than some dirt the tank is very clean. No rust either, indicating this car didn't sit half empty with water and moisture in it for any length of time.

Before we do anything stupid, let's test the new sending unit so we know the wiring to the gauge works...

And the tank is completely empty per the gauge, just like it should be!

New sending unit is installed! The return line is 1/4" where the original was 5/16". Not sure if this is a California thing as all '69 units in the catalog either indicate no return line or 1/4".

This is the fun part. Getting the tank back in with the sending unit attached and insulation in place. I had to scrounge for scrap wood and get to lie on my back with my knees at my chin to keep the tank in place while I tighten the braces down. It gives you bruises in the weirdest places.

New rubber lines from Gates with quality clamps.

Ground wire is installed barbs down for extra continuity goodness.

I have a kitty friend who likes to come hang out when I've got the garage open. She rubbed all over me while I was fighting the tank, it's nice to have a friend that cares!

After putting in 2 gallons, the needle moves up above the E mark a little bit. That means I've got a registering gas gauge again! Yay! Victory!

Pretty straightforward day, only one broken nut that caused trouble and the rest was easy. Fuel pump lines up front still need to be re-done when the new fuel pump is installed, but since the oil is changed, the plugs and wires are changed, and the new steering column is in, we're rapidly winding down the major projects. If the smoking goes away completely, I'll be ecstatic and be putting lots of miles on the car!

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Last updated June 7th, 2014