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R & R fuel tank sending unit.

 
Old 08-20-2018, 11:33 AM
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colo63sw
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Default R & R fuel tank sending unit.

My fuel tank sending unit is leaking a little bit on my 63 coupe.

Has anyone done the R & R of the sending unit WITHOUT removing the spare tire tub? It looks tempting to try.

Where would the best place be to go to get a new SU gasket?
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Old 08-20-2018, 11:44 AM
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I would recommend BOTH a new GM gasket and a new GM metal sending unit retaining ring. Both are available on Ebay, if you search under the original part numbers. I can provide if needed. Reproduction o-rings from OEM Reproductions are also very nice, and I would use it if I could not find the GM piece. I would not use anything else.

Soak o-ring in motor oil overnight or use Vaseline on it.

The sending unit requires a bit of "moving it around" inside the tank to get it thru the gas tank opening............but it can be done. If you have an original sending unit, the electrical posts (2) have adjustment nuts to provide sealing of these connections. Maybe you just need a simple adjustment of these retaining/sealing nuts.

Larry

Last edited by Powershift; 08-20-2018 at 11:45 AM.
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Old 08-20-2018, 11:49 AM
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I removed the spare tire tub to change mine. It was a little effort but resulted in easier access and visibility. Disconnect the battery while doing the work. C2 sending units are “powered”.
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Old 08-20-2018, 11:53 AM
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Originally Posted by Powershift View Post
I would recommend BOTH a new GM gasket and a new GM metal sending unit retaining ring. Both are available on Ebay, if you search under the original part numbers. I can provide if needed. Reproduction o-rings from OEM Reproductions are also very nice, and I would use it if I could not find the GM piece. I would not use anything else.

Soak o-ring in motor oil overnight or use Vaseline on it.

The sending unit requires a bit of "moving it around" inside the tank to get it thru the gas tank opening............but it can be done. If you have an original sending unit, the electrical posts (2) have adjustment nuts to provide sealing of these connections. Maybe you just need a simple adjustment of these retaining/sealing nuts.

Larry
Thanks for the suggestions, especially on the posts nut adjustments. I believe my SU is original.
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Old 08-20-2018, 11:55 AM
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Originally Posted by Frankie the Fink View Post
I removed the spare tire tub to change mine. It was a little effort but resulted in easier access and visibility. Disconnect the battery while doing the work. C2 sending units are “powered”.
Thanks for the battery comment Frankie, I did not think of that.
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Old 08-20-2018, 12:19 PM
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Here you go. https://www.ebay.com/itm/NOS-3774937...item1ee77168b6

If yu don't buy this kit, then search individually on Ebay using the GM Part #.

Larry
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Old 08-20-2018, 12:34 PM
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Originally Posted by Powershift View Post
Here you go. https://www.ebay.com/itm/NOS-3774937...item1ee77168b6

If yu don't buy this kit, then search individually on Ebay using the GM Part #.

Larry
Thanks!

Now I have a couple of questions:

1. What wears out on the cam retaining ring?

2. My needle has always been 'bouncy' on corners & stopping. I have written it off as some baffle missing/out of place in the tank. Could a bouncy needle be due to the sending unit?

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Old 08-20-2018, 12:46 PM
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Originally Posted by colo63sw View Post
Thanks!

Now I have a couple of questions:

1. What wears out on the cam retaining ring?

2. My needle has always been 'bouncy' on corners & stopping. I have written it off as some baffle missing/out of place in the tank. Could a bouncy needle be due to the sending unit?
Outside chance it’s the sending unit. Prob not. Some will tell you the dash gauge has lost its damping fluid. I went all through this earlier in the summer including trying 3 different gauges, repro, NOS, etc. They ALL bounce. I just live with it.
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Old 08-20-2018, 01:31 PM
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I just replaced one last week on my Camaro. It was very easy to test to see if it was the SU or the gauge because it’s a simple resistor and not powered. All you do is ground it to see what the guage does. Is there a similar test for the Corvete SU?

Ed
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Old 08-20-2018, 02:16 PM
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Originally Posted by colo63sw View Post
Thanks!

Now I have a couple of questions:

1. What wears out on the cam retaining ring?
It get old and corroded and loses its tension to seal the o-ring. If you feel lucky, don't replace it.

Larry
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Old 08-20-2018, 03:50 PM
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Originally Posted by emdoller View Post
I just replaced one last week on my Camaro. It was very easy to test to see if it was the SU or the gauge because it’s a simple resistor and not powered. All you do is ground it to see what the guage does. Is there a similar test for the Corvete SU?

Ed
Unlike C1s and C3s the C2 sending units are "powered" and use a voltage divider to measure fuel level (nobody knows why these years adopted the unnecessary complexity)... You can test the gauges and sending units for C1s and C2s following this document.

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Old 08-20-2018, 03:55 PM
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The problem with the repro rings and "O" gaskets are that the metal rings seem a tad smaller and if you don't get it EXACTLY centered you'll have leaks; likewise the repro "O" gaskets are smaller and don't always seal well and will leak. Having the sending unit tool for this job helps but a small hammer and brass "drift" will work but takes some effort to center the ring...

Guess which "O" ring is NOS ?

Last edited by Frankie the Fink; 08-20-2018 at 04:09 PM.
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Old 08-20-2018, 04:09 PM
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Originally Posted by Frankie the Fink View Post

The problem with the repro rings and "O" gaskets are that the metal rings seem a tad smaller and if you don't get it EXACTLY centered you'll have leaks; likewise the repro "O" gaskets are smaller and don't always seal well and will leak. Having the sending unit tool for this job helps but a screwdriver will work but takes some effort to center the ring...

Guess which "O" ring is NOS:
Hey Frankie,
When I removed my "O" ring from my tank, it still feels very pliable. I'm considering using the original "O" ring again. Do you think I should give it a shot?

Also to colo63sw,
I sent my sending unit (pretty sure original too), into John Wolf for a rebuild. Figured I would do it now, rather than put it together to find it didn't work. Something you may want to consider.

Pat

Last edited by ptjsk; 08-20-2018 at 04:10 PM.
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Old 08-20-2018, 04:11 PM
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If yours is original and not swollen to the point of not sealing, nor brittle, nor cracked -- hell yeah I'd use it...

I thought I'd never get my repro O ring to seal; a forum member took mercy on me and sent me an NOS O ring as a favor....that "sealed the deal"...

Install the "O" ring and put just enough gas in the tank to cover it an inch or two and let it sit overnight...if its OK add a few gallons more and recheck....after about 1/4 tank it should be fine if you want to fill it up...

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Old 08-20-2018, 04:15 PM
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I’ve never understood why a vendor would go to all the effort to make a repo part incorrect.

Last edited by pop23235; 08-20-2018 at 04:16 PM.
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Old 08-20-2018, 07:40 PM
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Photos below show an original AC sending unit (top photo) and a Fargo reproduction sending unit (bottom photo) - note the STAMPED "S" and "I" adjacent to the terminals on the original AC unit. Fargo was the best repro unit out there when I wrote the comparison article about eight years ago, but I think they've since gone out of business.

If you have an original AC sending unit, send it to John Wolf & Co. for restoration.

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Old 08-20-2018, 08:18 PM
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Originally Posted by JohnZ View Post
If you have an original AC sending unit, send it to John Wolf & Co. for restoration.
He's done a few for me and they work perfectly. Never had a leak using the available o-rings from all the common vendors. No need to search for an old OEM one. A little engine oil for lube is all that's needed.
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Old 08-20-2018, 09:41 PM
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Originally Posted by JohnZ View Post
Photos below show an original AC sending unit (top photo) and a Fargo reproduction sending unit (bottom photo) - note the STAMPED "S" and "I" adjacent to the terminals on the original AC unit. Fargo was the best repro unit out there when I wrote the comparison article about eight years ago, but I think they've since gone out of business.

If you have an original AC sending unit, send it to John Wolf & Co. for restoration.
Thanks John Z.

Here is a photo of my unit. Sorry about the focus, but it looks like there are stamped letters. Funny thing, I took the photo because I recalled a spade lug on the unit and thought it was one of the (I thought only 2) terminals. I am getting too old.



The new fuel line is my splice because I though the problem was a leaky FL connection.

Thanks again!

Last edited by colo63sw; 08-20-2018 at 09:43 PM.
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Old 08-21-2018, 07:32 AM
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My repro sending unit had the stamped "S" and "I" letters at the terminals....it also had "90 ohms" stamped on the internal mechanism...

The "I" is the switched 12V from the ignition (remember C2 units are "powered") and the "S" is the wire from the gauge to the wiper of the sending unit's voltage divider circuit...

The difference in the NOS and repro "O" rings is blatant - if you play with a repro part enough I guess you can make anything work......

Here is the 1967 GM Chassis Manual procedure for R&Ring the Corvette sending unit - nothing about soaking the gasket in any goo - it does nothing but make it slippery and hard to install as you'll find out when its slithering around in its groove while you're trying to get the retainer ring on while working upside down...

The "soaking in oil" step is needed to swell the smaller repro gaskets; not required on correctly sized NOS versions. I don't use any oil and GM didn't think it necessary either.

The MOST important thing is to clean that gasket groove and the back of the retainer ring thoroughly - I use lacquer thinner and a lint free rag.



Last edited by Frankie the Fink; 08-21-2018 at 08:21 AM.
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Old 08-21-2018, 08:35 AM
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GM did indeed use engine oil and Quanta recommends it as well when replacing the sending unit. Here's a previous thread on the subject for the non-believers - https://www.corvetteforum.com/forums...ding-unit.html
Repo. seals work perfectly IF they are installed correctly.

JohnZ states - "In the plant, we kept the fat rubber O-ring seals in a tray of motor oil for several hours before installing them; the requirement to do that is in the Assembly Manual, in the "Lubricants" section that decodes the lube symbol on the sheet that shows the installation."

Last edited by 1snake; 08-21-2018 at 09:02 AM.
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