727 return line leak at tranny fitting

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68 Coronet RT

68 GTS # 508 in Registry
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The one thing that drives me crazy is a fluid leak. I have replaced the return line tranny fitting twice and even replaced the return line and it still leaks at the fitting where the line and fitting meet. Could it be the fitting I don't know. I bought the fittings at NAPA, brass with a tapered thread like they are suppose to be but I'm wondering if the end where the return line connects is subject. Has anyone had this issue ? Is there a better fitting out there than the one's from NAPA. It's not the shift shaft seal, I had that replaced and that is bone dry. I can run my finger around the return line fitting and she's wet. Any Idea's ?
 
At work we use copper or aluminum conical seals to help stop tapered fittings from dripping when they just won't seal no matter how tight they are.

They really do work. I think the trans fitting is 5/16 (-5)

https://www.gen-aircraft-hardware.com/images/pdf/as4824.pdf

image.jpeg
 
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Yep, those conical seals work well. I too have used them in aviation. Are you sure the trans case isnt cracked from overtightening the pipe thread?
 
Did you use sealer on the fitting where it screws into the case? I use ARP thread sealer but even regular pipe dome meant for water pipes works
 
the inside of the brass fitting is supposed to be inverted flare, like a brake line or fuel line. Did you do the double flares on the lines yourself, or did you buy pre flared straight lines? If everything is done correctly, it should not take a huge amount of torque to get the connection to seal.
 
Yep, those conical seals work well. I too have used them in aviation. Are you sure the trans case isnt cracked from overtightening the pipe thread?

Nope not cracked, the area where the fitting screws into the tranny is reinforced and the tranny shop where I took it to have the shift shaft seal replaced said that it pretty hard to crack the there. They said I could snap the fitting off before it would crack the case. They did say they have seen the case crack where in the back where the other fitting is because of over tightening
 
At work we use copper or aluminum conical seals to help stop tapered fittings from dripping when they just won't seal no matter how tight they are.

They really do work. I think the trans fitting is 5/16 (-5)

https://www.gen-aircraft-hardware.com/images/pdf/as4824.pdf

View attachment 1715226644

Thanks scatpactbee, I ordered two aluminum and two copper. $1.75 each. Hopefully one of these will work. Now I'm fighting trying to get my steering box out that crapped out on me last week. No fun looks like I'm going to have to pull the exhaust manifold to get it out.:wtf:
 
Thanks scatpactbee, I ordered two aluminum and two copper. $1.75 each. Hopefully one of these will work. Now I'm fighting trying to get my steering box out that crapped out on me last week. No fun looks like I'm going to have to pull the exhaust manifold to get it out.:wtf:

Just to give a little update on my leaky fitting issue. I ordered two OEM return line fitting and received them today. I compared them to the ones I bought at NAPA. No comparison the OEM fittings are a 1/8 inch longer. The thread end that goes into the case is longer, the conical end looks to be the same angle but the angle is longer. Without a comparator I really can't tell if the angle is the same but the angle is definitely a little bit longer on the OEM fittings. The nut on the OEM is also larger it's 9/16 instead of a 1/2 inch on the NAPA fittings. The seals I ordered will be here tomorrow and I'm going to wait till tomorrow to put it back together. Stay tuned ! I did get my steering box out, didn't have to remove the exhaust manifolds, ended up dropping the exhaust pipe on that side and with a little wiggle she fell right out.
 
Just to give a little update on my leaky fitting issue. I ordered two OEM return line fitting and received them today. I compared them to the ones I bought at NAPA. No comparison the OEM fittings are a 1/8 inch longer. The thread end that goes into the case is longer, the conical end looks to be the same angle but the angle is longer. Without a comparator I really can't tell if the angle is the same but the angle is definitely a little bit longer on the OEM fittings. The nut on the OEM is also larger it's 9/16 instead of a 1/2 inch on the NAPA fittings. The seals I ordered will be here tomorrow and I'm going to wait till tomorrow to put it back together. Stay tuned ! I did get my steering box out, didn't have to remove the exhaust manifolds, ended up dropping the exhaust pipe on that side and with a little wiggle she fell right out.

I saw in your original post that you replaced the "line".
Was this a new steel cooler line?
The reason I ask is because sometimes the flare cracks and it's really hard to notice.
Even hard to see.
 
I saw in your original post that you replaced the "line".
Was this a new steel cooler line?
The reason I ask is because sometimes the flare cracks and it's really hard to notice.
Even hard to see.

I had originally thought that my original return line was leaking so I bought a set of lines off ebay and replaced the return line only. They were suppose to be direct fit but were anything but. I then put my original line back on and it actually leaked a little more but once I removed the fitting I could see why it leaked as the end of the fitting where it connects to the line actually had a dimple in it from the return line. I don't know the hardness of the brass that the NAPA fittings are but it seems awful soft. I plan on pulling the original line off again and checking it with a magnifying glass to see if there is any cracks. The after market line actually leaked less but looking at both ends together the flares are not the same, the original line I think has a better flare. I wish I knew someone around here with a magnaflux machine that I could check the ends for cracks. The cracks would stick out like a sore thumb.
 
I had originally thought that my original return line was leaking so I bought a set of lines off ebay and replaced the return line only. They were suppose to be direct fit but were anything but. I then put my original line back on and it actually leaked a little more but once I removed the fitting I could see why it leaked as the end of the fitting where it connects to the line actually had a dimple in it from the return line. I don't know the hardness of the brass that the NAPA fittings are but it seems awful soft. I plan on pulling the original line off again and checking it with a magnifying glass to see if there is any cracks. The after market line actually leaked less but looking at both ends together the flares are not the same, the original line I think has a better flare. I wish I knew someone around here with a magnaflux machine that I could check the ends for cracks. The cracks would stick out like a sore thumb.
with a little practice and a good brand flaring tool (like Mac, BluePoint, Strap-on, etc) you can make your own lines.
 
I had originally thought that my original return line was leaking so I bought a set of lines off ebay and replaced the return line only. They were suppose to be direct fit but were anything but. I then put my original line back on and it actually leaked a little more but once I removed the fitting I could see why it leaked as the end of the fitting where it connects to the line actually had a dimple in it from the return line. I don't know the hardness of the brass that the NAPA fittings are but it seems awful soft. I plan on pulling the original line off again and checking it with a magnifying glass to see if there is any cracks. The after market line actually leaked less but looking at both ends together the flares are not the same, the original line I think has a better flare. I wish I knew someone around here with a magnaflux machine that I could check the ends for cracks. The cracks would stick out like a sore thumb.

When I swapped my lines to 3/8 I used a combination pipe thread/compression union fitting and they worked out really well.
That ditched the flares, and made any future repairs needed in that area a lot simpler.
They make them in brass or steel either one, but the brass has been leak and trouble free for a couple of years of daily driving.

Untitled.jpg
 
When I swapped my lines to 3/8 I used a combination pipe thread/compression union fitting and they worked out really well.
That ditched the flares, and made any future repairs needed in that area a lot simpler.
They make them in brass or steel either one, but the brass has been leak and trouble free for a couple of years of daily driving.

View attachment 1715228489
I used that style compression fittings on my brake lines when I installed my line loc (specked to brake line pressure of course) and they work great
 
After weeks and weeks of messing around with the return line I just couldn't get it to stop leaking. I took TrailBeast suggestion and I put a compression fitting in. I should have done that weeks ago as it would have saved me much aggravation. She's dry as a bone, no more leaking. Now I can move on to the next leak, my oil pan. These old cars always have some to work on, I guess that's why we love them !
 
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