New Gas Tank Sending Unit Leaks

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69KillerFish

69KillerFish

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Hey guys, I just replaced my gas tank sending unit in my 69 Cuda last weekend. The new unit works, it is a nice feeling knowing how much gas you have in your tank! Filled it up and went to a show last weekend, no problems. Which, brings me to the problem. Went out today to get my car ready for another show this weekend. I noticed a strong odor of gas. I look under the car and there is a puddle of gas on the concrete. I could see gas dripping down off the edge of the tank right below the new sending unit. When I parked it, there was 3/4 of a tank. It is now down close to a third of a tank. It has to stop at some point when the gas reaches below the edge of the new sending unit seal right? Now, this is the first time I have changed a sending unit. I am wondering if I did something wrong. I put the gasket between the sending unit and the tank and then turned the outer ring to secure it. Should I have added some kind of gasket sealant on the gasket? Both sides? Which is gas friendly?
 
Sarcasm tells me the new ring was the wrong answer...? let me guess: Too thin?
 
69KillerFish said:
Yeah, I did. I am starting to get that stupid feeling....
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Well, don't, you ain't alone, lol. For some reason those new lock rings don't put enough pressure on the sending unit/seal.

If you have the old one, I hope, put it in. Make sure and tap the ring so those little tangs seat in the slots.

By the way, try and use something brass if you can, sparks baaad.
 
You can try and bend those tangs out a bit. If need be, pull the gasket out and make another one by tracing that one onto some thinner gasket material. You should be able to find some at a parts house.

Put it back together with the gasket you have now between the sender and the tank, put the thinner one you made between the sender and the lock ring. That should be enough to tighten it up.

Just try and use a brass punch if you have one, to set the ring, to eliminate the spark thing.

Also don't just tap on one area, move from tang to tang to help keep it from walking to one side.
 
The new lock rings and gaskets are junk. Even using an old lock ring I had issues with the standard gaskets. I started getting my gaskets from DMT, he makes them himself and they're a better fit than the normal chinese junk. http://www.ebay.com/itm/DMT-Mopar-57-91-A-B-C-Body-Fuel-Lock-Ring-Sending-Unit-to-Tank-Seal-/360751319879

Sometimes the lock rings get tweaked too, I usually adjust the tabs on them anyway. I also install them with a large set of channel lock pliers, its easier to control how the lock ring seats than tapping on it with a punch.
 
I had the same problem with my '67 Barracuda and my son's '70 Roadrunner. The tanks were fine but I had a devil of a time getting a good seal with those new lock rings. On one tank we were able to find and re-use the old ring. - On the other one I put some Permatex AVIATION FORM-A-GASKET #80019 on the rubber seal and forced the locking ring about an eighth of an inch past the rotational stops. I was pretty conservative with the sealant because I wasn't sure if it was soluble in gas. I figured as long as I could get it sandwiched between the tank and the gasket with a thin coat I'd be OK.
 
Same problem here. Fought it for two weeks. Different thicknesses of gaskets, different sealers, etc. Read the forum, found my old ring, problem solved. If you can't find your old lock ring, post in the parts wanted section. Lots of guys parting cars and that is a pretty common part that doesn't wear out.
 
I will try to find ny ring. If not, I will ask in the parts section for an old one. Thanks so much for your help!
 
There isn't a good way to bend any metal and improve the fit.
The goal would be to close the space between the tank wall and the retainer that is welded on the tank. Sure you could capture the gap in channel lock pliers but... If the tank wall bends instead of the retainer, you're screwed. The tank wall and the flange on the sender need to be flat. The retainer and lock ring can be distorted since hey only pinch the gasket between 2 flats.
Best plan is make the new seal ring act as thicker. Use a rounded punch to put some dimples in its flat surfaces. Dimples toward the retainer will likely work better than dimples toward the sender.
 
I used the RTV gasket maker. I put a thin coat on the tank and then put in the gasket. I put another coat over the gasket, then put in the sender.
Again another thicker coat over the sender, then put in the ring.
I added more around the outside and inside of the ring.
Sounds gooey, I know.
I left it to cure at least over night. Then added a small amount of gas. and tipped up the tank so the gas covered the seal
first time I had a small leak. so I put more gasket maker around the ring, let it set
tipped the tank up again looked for leaks.
It works with no problems

Ed
 
I just found my old lock ring. I had pitched in the trash can. Fortunatly it was still there. This proves that old adage that you should never throw your old parts away. I will give the old lock ring a try a let you guys know how it turns out. Thank you very much!
 
69KillerFish said:
I just found my old lock ring. I had pitched in the trash can. Fortunately it was still there. This proves that old adage that you should never throw your old parts away. I will give the old lock ring a try a let you guys know how it turns out. Thank you very much!
Click to expand...

:thumleft:
 
69KillerFish said:
I just found my old lock ring. I had pitched in the trash can. Fortunatly it was still there. This proves that old adage that you should never throw your old parts away. I will give the old lock ring a try a let you guys know how it turns out. Thank you very much!
Click to expand...

Would be interesting to know the relevant size differences of the new and old lock rings.

Maybe a few spots of weld and a grind could help the new rings seal?
 
i' m sure the supplier/ manufacturer/importer whatever is aware of their crap problem!!!!!!! wish I could shove some of this inferior made "stuff" where the sun doesn't shine!!!????? juat me......
 
Killerfish - I had the same problem with mine what I did was go down to HomeDepot and bought a drain gasket, went back and doubled it up with my old one and worked like a snap
 
not just any old piece of gasket material is fuel stable. Even the OEM material struggles with todays ethanol. Not long ago there was a batch of filler neck seals that turned to jelly. just saying...
 
Redfish - I agree, was my worry as well - why I used my old one closer to the tank and the new one was as spacer. To this day after using multiple fuels, its still working fine. and I did test it in fuel before - accidentally, still no issues (Dropped in fuel tank like a dummy) Not saying all are like this, but the one I have is
 
Finally had a chance to get the sending unit out and fix the seal. After really comparing the new retaining ring against the old one, I am shocked to see the difference in quality. The new ring appears to be a cheapo stamped out piece of crap metal. The original one, nice thick sturdy ring. Why I didn't catch this in the first place, I don't know. Anyways, after taking in all the advice from above. I decided to re-do this only once. I cut another matching gasket from thinner material and put the two gaskets back to back and added a tiny bit of gasket sealant (fuel tolerant) to keep them together. I put the rubber one against the tank and the thinner one against the sending unit. I tightened the assembly down using the old locking ring. What a difference, nice solid seal. I won't find out if it leaks until this weekend when I get it out to fill up the tank again but, I am confident it won't.
 
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