C2 Fuel Smell and Sending Unit Cam
After filling up my gas tank the other day, I noticed a fairly strong fuel smell when I returned home. I always fill up well below the filler neck to avoid any overflow into the rubber boot. The smell wasn't nearly as strong today upon returning from a 40 minute highway and local drive. However, I still smell some gas which I haven't noticed before. I pulled up the rubber overflow boot and didn't see any staining around the filler neck, but when I took a look at the sending unit under the car, I see some "dampness" around the sending unit cam. Some of it looks thicker like dried fuel that has been there a while, however I can see a little wetness in some spots when I shine a flashlight on it. The sending unit was replaced about 4 years ago and a new gasket was installed. Can the sending unit cam be tightened like a threaded nut, or does it just twist and lock in place? If it can be tightened, what tool can I use without buying a specialty tool? If it can't be tightened, I suppose a new gasket, o-ring seal, and cam will be necessary?? Thank you for your assistance, Roger (50141)
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Re: C2 Fuel Smell and Sending Unit Cam
Roger:
Cam cannot be tightened like a screw, but it does have a 1/2 inch or so of raised seating area......so make certain that it is installed/turned as far as it can go against the stops.
I have found that non-GM replacement cams do not provide the correct seating force on the o-ring. So make sure to get a GM o-ring and replacement cam. DR REBUILD had these for sale awhile back, or order through GM. Soak the o-ring in motor oil overnight or use Vaseline on it. You can use a brass (non-sparking) drift and small hammer to remove/install the cam, but Long Island Corvette Supply (and others) have a special tool that is not very expensive. That is what I have/use.
Also check the retaining nuts on the electrical connections for tightness. Original sending units have packing/seals at these connections that can be tightened. Often they go to leaking a bit.
Larry -
Re: C2 Fuel Smell and Sending Unit Cam
Hi Larry, thank you for your reply. I will take a closer look to see if the cam can be tightened any more. Assuming that it is tightened properly, then I will purchase a new sending unit. The one that came with my car was a non-functioning replacement. This one has been working, but it isn't accurate. So, if I go through the bother of removing the sending unit to replace the o-ring, I will get a new unit and hope that it provides a more accurate reading. Does anyone know where I can buy the best sending unit? The Fargo Automotive units don't appear to be available from any source. Eckler's offers two units; a reproduction (probably the same junk I have in my car now) and a "GM Restoration" part made for ethanol, correct for judging, and made in the USA. Is this the best unit available? Paragon also offers two sending units (one is more expensive than the other).
... I just want to make sure that I buy the best/most accurate one on the market. Any thoughts? Thank you, Roger (50141)
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Re: C2 Fuel Smell and Sending Unit Cam
Sorry to hear about your problem Roger. I'll be installing the fuel tank on my chassis soon and I noticed that Quanta sells a sending unit tool for installing the locking cam. Should I plan on buying one to get the sending unit installed correctly?
MikeComment
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Re: C2 Fuel Smell and Sending Unit Cam
Hi Mike. I believe you can install the locking cam without the tool - especially on a rolling chassis - but for under $20.00, I think it's worth the small investment. There's a good chance that I will be buying one, too, in order to either tighten the existing cam or to replace the sending unit and to ensure full locking of the new cam. Unfortunately, I first have to go out for a long drive and burn off the nearly full tank of gas from my recent fill-up
. Roger (50141)
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Re: C2 Fuel Smell and Sending Unit Cam
Sorry to hear about your problem Roger. I'll be installing the fuel tank on my chassis soon and I noticed that Quanta sells a sending unit tool for installing the locking cam. Should I plan on buying one to get the sending unit installed correctly?
Mike
This looks like the tool that LICS has been selling for years, and is exactly like the one I have. Also, take my advice above, and buy a GM-made sending unit retaining cam and o-ring for your Quanta tank. Cost is cheap. That way you should only have to do the job once.
LarryComment
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Re: C2 Fuel Smell and Sending Unit Cam
Roger Use an O'ring made out of viton rubber for ethanol. McMaster Carr, MSC, etc. Trouble is you will have to buy them in quantity. JDComment
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Re: C2 Fuel Smell and Sending Unit Cam
John,
Do you have a McMaster Carr or MSC item number for the correctly sized viton rubber O-ring? When you say you have to buy multiples, are you talking qty=5? Or more?
GaryComment
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Re: C2 Fuel Smell and Sending Unit Cam
Mike, Larry, and John... thank you for your replies. I am going to take a closer look at the locking cam tomorrow to see if it just needs to be tightened a little to stop the seepage. I don't have a dripping leak, but I see dried/gummy gas and some shiny moisture around the perimeter of the cam. I also see a discoloration/film on the back side of the spare tire carrier (I assume from gas). If I determine that the o-ring has to be replaced, then I will buy a new sender since the 4 year old sender has never read accurately from Day 1. Unless someone has a better suggestion, I will buy the "GM Restoration" sender from Eckler's since it claims that it will pass judging and that is it built to E85 specs for ethanol. Paragon sells two senders, too (one is about $10.00 more than the other) and also claims to be a GM Restoration part, but it looks different than the Eckler's sender and doesn't say anything about being built for ethanol fuel. This fairly simple task is getting complicated! I believe by the mid-70's GM engineers realized that installing the fuel sending unit on the bottom of the gas tank was a bad idea and moved it to the top of the tank. Hello!! Thank you, Roger (50141)Comment
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Re: C2 Fuel Smell and Sending Unit Cam
Roger------
This gasket is NOT a simple o-ring. Among other features, it has a tab on the inner circumference and I believe the purpose of this tab is anti-rotation. Could a simple o-ring of the same cross section be used? Probably, but GM put a tab there for a good reason, whatever that reason is. I really doubt that these gaskets will be degraded to any significant degree by E-10 gasoline. E-85 fuel is not compatible with your vehicle, regardless of what fuel sender gasket is used.
The reason that the fuel tank sender/pick-up unit changed for 1975 was because the design of the tank system changed. Beginning with 1975, the fuel tanks had a bladder installed. So, the previous sender/pick-up configuration was impractical. A new sender/ pick-up with integral fuel filler was used.
Attached below are photos of the GM/Kent-Moore fuel sender cam tool, J-23346, which is applicable to all 1963-74 Corvettes. This tool can often be found on eBay but I think the aftermarket tool pictured above should work just as well. I do not recommend the use of a punch-and-hammer to install the cam.
DSCN2912.jpgDSCN2913.jpgDSCN2914.jpgIn Appreciation of John HinckleyComment
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Re: C2 Fuel Smell and Sending Unit Cam
Gary, I have no idea what the size is. Someone provide the size and I will look it up. Typically o'rings are sold in bags or 50 or 100. Very large o'rings are sold in bags of 25. But don't quote me on that. When I order O'rings I order huge amounts.
Viton o'rings come in two colors. Brownish and semi flat black. They are not real smooth to the touch like buna rubber o'rings.
All the industrial tool companies have web sites but I would be happy to do the initial leg work. JohnComment
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Re: C2 Fuel Smell and Sending Unit Cam
Don't know if you might still have your original GM fuel sender, but if so it can be rebuilt. That's what I did after getting tired of replacing the crappy repros. The positioning of the O ring on sender is important. It's got to be centered as the cam is tightened. Be sure to give it a light coating of oil. Never had a leak, just electrically bad sending units. DanComment
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Re: C2 Fuel Smell and Sending Unit Cam
From my research, it looks like the Eckler's "GM Restoration" sender is the one I will buy since it is made in the USA and is ethanol-resistant. I have a couple feelers out for a Fargo Automotive sender, but it appears that they are now extinct. Unfortunately, my original sender is long gone. I called John Wolf to see if they have any restored original senders for sale, but that would be a big N-O. I attached two photos that I shot tonight showing the bottom of the sender and gas tank. The seepage extends to the outside of the raised ring that the cam tightens against. Is that from capillary action, or is the gas actually seeping through the tank where this ring is mated to the tank? I still think the gas seepage is from the o-ring, but now I'm not certain. Hmmm, the plot thickens like seeping ethanol. What do you think? Roger (50141)Comment
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Re: C2 Fuel Smell and Sending Unit Cam
Roger:
As I stated earlier, I would also check the electrical connection seals. They are usually the first to leak. Originals and some reproductions can have the connection seal/packing tightened up. The electrical connector seals on some reproductions cannot be tightened.
LarryComment
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Re: C2 Fuel Smell and Sending Unit Cam
Thank you for the suggestion, Larry. I will take a closer look at the connections this weekend and will post my findings. Roger (50141)Comment
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