Help! Replacing fuel tank sending unit

[bwing]

I have a 1966 coupe w/327 and have no experience working with gas tanks. I noticed gas dripping from the bottom of the tank. When I jacked up the rear end I noticed the gas was dripping from a prong protruding from the center of a round snap ring. The prong has a rubber gasket surrounding a white plastic piece. The prong has a "S" stamped next to it so I'm assuming it's the gas sending unit. I emptied the tank of gas. Can anyone tell me if this can be repaired without having to remove the gas tank? Is it a simple repair? Looking down into the tank I noticed a float. Is this in anyway connected to the sending unit? I'm assuming yes. There is also a 2nd prong with an "I" stamped on the plate and that prong is sticking straight down like the "S" prong. Thank you for any help any of you can offer.

 

[WayneC]

Disclaimer: I've only changed the tank sender with the tank removed from the car.

If you don't have a shop manual, you ought to acquire one. Yes, what you are looking at is the gauge sending unit (yes, the float is attached to that assembly), and it sounds as though yours is leaking. According to the shop manual, you first need to remove the spare tire tub, then you should be able to remove the sending unit. It is clamped in place over a large O-ring by a circular "gauge retainer cam"... that circular clamp is installed using a special spanner tool (available from vendors, see below) to rotate it into place, squeezing the O-ring beneath it.

You may be able to remove it by tapping the clamp "ears" in the desired direction with something non-metallic, for example using a 1x1 length of wood as a "chisel" and tapping it with a hammer. Obviously you want to do everything possible to avoid generating any sparks, so a plastic-coated hammer with the wood "chisel" would be prudent. The question is whether you have enough access/clearance under there to maneuver the tools in the needed positions to remove/replace the clamp. I'd recommend buying the tool, it's not expensive and well worth it for the convenience.

Installing the new sending unit would be done the same way; you might want to apply a thin coat of silicone grease to the rubber O-ring before installing it, to ensure you don't tear it in the process.

Tool, sending unit and O-ring are available from vendors. Search on parts 05-38a, 05-39c, 05-39a, 05-39b at this website:
http://www.licorvette.com/ (click on "shop online)

Hopefully others who have accomplished this task will chime in.
It would be easier to remove/install the sending unit if you first remove the tank, but that will also require you to remove the filler gasket, exhaust pipes, and tank retaining straps.

 

[bwing]

When I purchased the '66 a year ago, the seller shipped all paperwork and a 1966 manual with the car. The manual says to remove the spare tire carrier and the rest can be accomplished without having to remove the tank. It did say you had to remove the tank if it was the optional 36 gal tank. I guess I'll have to take a better look once I actually start repairs. I ordered the sending unit and a spanner tool from Zip-Corvette today before I read your reply. I appreciate all the info you sent me as it will help me when "attempting" this repair. hnoes

Installing the new sending unit would be done the same way; you might want to apply a thin coat of silicone grease to the rubber O-ring before installing it, to ensure you don't tear it in the process.

Good tip using the silicone grease. Thanks.

 

[JohnZ]

Just to clarify - the big rubber O-ring goes between the sending unit flange and the tank, not between the cam ring and the sending unit flange; it's not subjected to any motion during installation.

 

[bwing]

Just to clarify - the big rubber O-ring goes between the sending unit flange and the tank, not between the cam ring and the sending unit flange; it's not subjected to any motion during installation.

I can't quite picture what you're saying JohnZ since I haven't started the repair or removed the leaking unit. The replacement unit was shipped yesterday and will arrive next Tuesday. Thanks for the info though because I was thinking the gasket went between the cam ring and the sending unit. I think I'm going to be in big trouble. hnoes

 

[JohnZ]

I can't quite picture what you're saying JohnZ since I haven't started the repair or removed the leaking unit. The replacement unit was shipped yesterday and will arrive next Tuesday. Thanks for the info though because I was thinking the gasket went between the cam ring and the sending unit. I think I'm going to be in big trouble. hnoes

The installation is shown in your '66 Assembly Manual in UPC 8, Sheet B1.

 

[bwing]

Thanks to all who responded. It was an easy repair/installation. To anyone doing this I recommend purchasing the spanner tool. Makes it a lot easier to remove the cam ring.
I did it by removing the spare tire carrier only. I did not remove the gas tank. Removing the old sending unit was uneventful. When installing the new unit, take your time, as you do not want to rip the net filter or any wiring. Make sure the round seal is in place before you install the unit. After you have it inserted and seated properly replace the cam ring using the special tool to tighten it. Add a few gallons of gas to check for leakage.