Fuel Tank Sending Unit Replacement

My fuel gage stopped working and at first I thought it was that dreadful little voltage regulator buried behind the instrument gage cluster that had gone bad because the temperature gage did not seem to be working either. However, when I checked the voltage at the fuel tank sending unit, it read about 10 volts which indicated the regulator was working. When I checked the resistance across the fuel tank sending unit, it was basically an open circuit, indicating that the sending unit was inoperative.

A week or so later, I received a replacement sending unit and float from Delta Motorsports. First thing I did, for future reference, is to measure the new sending unit resistance empty (260 ohms) and full (25 ohms) and take some pictures (below). Then I began thinking about how to go about the replacement - it should be simple, right?

First, did I have to remove the fuel tank to make the switch? The people on JHPS bulletin board had mixed opinions, so I decided to try replacement without removing the tank. After pumping the gas out of the tank into various fuel containers, I removed the rug and gasoline tank cover, disconnected the fuel lines, and with a gentle bump to the sending unit retaining ring, the sending unit was free. So far so good. Next, I snaked the float out of the tank, no problem, it came right out without removing the tank.

Snaked the new sending unit in the tank opening (used new gasket) and applied the same retaining ring I had taken off. Using a hefty screw drive I tapped on the ears on the ring to tighten it in place. All was fine.

Next in went a couple of gallons of gasoline - the gage seemed to be working - Yessss. I didn’t want to put the old gas back in the tank so I threw a few tools in the boot and started toward the local gas station. By the time I reached the exit from my neighborhood, the engine quit running. Suspecting the fuel filter, I removed it and much gunk came flowing out - obviously a problem. I had a spare with me so I installed it. The engine still would not run. I took the hose free from the fuel pump and blew back through the pickup tube into the fuel tank and it seemed to be clear. Next I took the banjo fittings off the fuel pump and what did I find? The intake banjo was completely plugged with rust and debris. Evidently I had stirred up some bad stuff in my tank. After cleaning the pump out and reassembling it (all along the side of the road) the engine started and I drove home, resigned to removing the tank and cleaning it out. Again I removed the fuel level sending unit.

Taking the tank out was real easy since I had had it out before and remembered basically how to do it. I had previously replaced the mat underneath it with some rubber strips, and had rust-proofed the bottom of the tank. After removing the tank I flushed it with water and tons of crud came out. No wonder everything was plugging up. I threw a few rocks inside and banged them around inside until the water was clear coming from the tank. Next I hooked my vacuum/blower to the inlet and, leaving the tank in the sun, blew air through if for 4 hours to make sure it was dry.

After reinstalling the sending unit, the tank went back in and was hooked up once more. With a couple of gallons of gasoline back in the tank, I was confident the job was done, and headed for the service station again. After filling the tank to the top, I decided to peek in the boot, and to my anguish, there was gasoline leaking out of the tank onto the boot floor. After quickly stuffing some rags under the sending unit, and not having anything else I could do, I headed home. By the time I got home, things were pretty sopping with gasoline in the boot. Again the tank had to be emptied, this time into any container I could find. Finally the level was low enought that the leakage stopped.

The next day the sending unit came out again. I had meanwhile bought some Permatex Hylomar HPF Gasket Dressing and Flange Sealant to help assure no more leaks. After gooping both sides of the gasket with this compound, I reinstalled the sending unit and dogged it down with the retaining ring. In order to get the retaining ring to evenly apply pressure on the sending unit and gasket, I had to do a little bending of the dogs on the ring itself and the ears on the tank fitting itself that the dogs wedge against. All this done, and with the fuel pump hoses reconnected, fuel was added to the tank again, this time a little at a time. Voila, no leaks, nor have there been any since then.

What started out as an hour project had taken a day and a half. As an aside, I also added a fuel filter in the engine compartment just before the carburetors, and added a can of gas-dry to the tank.

Click for a lar ger picture

[Home] [Pictures] [Manuals] [Wiring] [Dellorto Conversion] [Maintenance Projects] [Fuel Tk Sending Unit] [Headlight Relays] [Pertronix Ignitor] [Tonneau Replacement] [Using Carbtune II] [Fuel Tank Renewal] [Front Supension Rebuild]