47-55.1 SBC 350 leaking fuel pump line

[NeoJuice]

Motor is SBC 350 with Edelbrock 1721 mechanical fuel pump.

Ever since putting fuel in the tank and doing a couple first start-up’s I've had a slow fuel leak on the input to the fuel pump. There braided supply lines and AN fittings the previous owner put on the truck.

The braided AN fitting goes into an adapter then into the 3/8’NPT inlet of the pump. I wouldn’t say it’s a leak but every time I look there is a drop just waiting to fall off onto the ground but it doesn’t. I dry it off and check it a day or two later and there is a drop dangling there.

The braided line is not leaking going into the adapter. It’s leaking where the adapter goes into the pump threads.

I first tried to tighten up the adapter that goes into the pump. Still a drip forms.

Secondly I know I can’t use white Teflon tape on fuel lines so I went out and got some Permatex Aviation form a gasket. I slowly backed out the fitting on the pump until it had a very very slow drip of gas that I could catch in a bucket. Smeared the permatex on is and let it set for a couple minutes before tightening it back up. At this point I thought ‘yes’ that should do it. Gave it a day or two and still the drip below the inlet.

After reading over the ‘features’ it says slow drying, non-hardening sealant. So is that my problem? Do I need a new adapter? Is there another type of Teflon tape or goop I should purchase?

At this point my options are.

-Get my truck to the exhaust shop so I can idle the truck until the tank is empty. (only put 20L in the tank)

-Once the gas is gone then I can remove the line and put more permatex on it. Let it dry properly then re-install the line to the pump then refill and test.

-Remove the line from the pump and drain the gas into a container and store it until the line is fixed. The problem is because I have the in cab tank and no petcock shut off valve to the tank, gravity to the inlet hose will drain until the tank is empty. And also since its not a rubber hose I just cant jab something like the opposite end of a drill bit to plug the line.

Anyone who reads this I appreciate any feedback or input.

[dsraven]

check under the cab to see if there is a rubber line there. if so, you can pinch it off with some hose pinch pliers or clamps. then go to the pump end, drain the fuel and let the line sit until it stops dripping and you can work in the area. check all the threads and fittings for cracks or thread damage. the inlet to the pump is a pipe thread which is tapered so you could use some pipe sealant on there, not the tape because it can shred as the fitting is screwed in and some can end up in the fuel system. there is some stuff plumbers use called pipe dope and it is pretty good stuff. it is a semi liquid paste. put it on dry though,no fuel on the fittings or in the connection anywhere. apply to the male part and then screw the parts together nice and tight. undo the pinch clamp and see if that fixed it. if not then look at the fittings again and also the part where the flex line attaches to the fitting, possible leak there under the braid?

[dsraven]

also look at the seal where the 2 halves of the pump come together. the screws are missing there because of the fitting connection. put something like a kids crayon on it and see if the fuel makes the crayon go away in that spot. if it does then a new pump may be in order or at least see about sealing that area of the 2 halves.

[MD2020]

I bought some air compressor line fittings for my air tools 1/4" NPT, yours should be 3/8"NPT, any way mine would not quit leaking so I put in a new one and it quite leaking.
both were new and had tape on them. Lot's of stuff comes from over seas, not the best sometimes.

[NeoJuice]

Originally Posted by dsraven

check under the cab to see if there is a rubber line there. if so, you can pinch it off with some hose pinch pliers or clamps. then go to the pump end, drain the fuel and let the line sit until it stops dripping and you can work in the area. check all the threads and fittings for cracks or thread damage. the inlet to the pump is a pipe thread which is tapered so you could use some pipe sealant on there, not the tape because it can shred as the fitting is screwed in and some can end up in the fuel system. there is some stuff plumbers use called pipe dope and it is pretty good stuff. it is a semi liquid paste. put it on dry though,no fuel on the fittings or in the connection anywhere. apply to the male part and then screw the parts together nice and tight. undo the pinch clamp and see if that fixed it. if not then look at the fittings again and also the part where the flex line attaches to the fitting, possible leak there under the braid?

There is no rubber line under the braided hose. These lines were made specifically for the truck by the previous owner.

The AN or NPT fitting on the braided line is not leaking it's the adapter piece like attached image in blue that goes into the fuel pump. So I will need some pipe dope as you said. I was trying to find something that was safe to use with fuel. Is this the stuff you are talking about?

https://www.homedepot.ca/en/home/p.p...000421131.html

I've included pictures of the hose coming off the tank. The pictures are old before I got the drive shaft in.

[NeoJuice]

Originally Posted by MD2020

I bought some air compressor line fittings for my air tools 1/4" NPT, yours should be 3/8"NPT, any way mine would not quit leaking so I put in a new one and it quite leaking.
both were new and had tape on them. Lot's of stuff comes from over seas, not the best sometimes.

Thanks for the suggestion. I have no problem picking up a new fittings but the problem is I only know the pump side is 3/8’NPT and dont know what the size of the braided line is.

[NeoJuice]

Originally Posted by dsraven

also look at the seal where the 2 halves of the pump come together. the screws are missing there because of the fitting connection. put something like a kids crayon on it and see if the fuel makes the crayon go away in that spot. if it does then a new pump may be in order or at least see about sealing that area of the 2 halves.

From the factory there is not a screw in each hole. I checked all the screws and they are tight.

[dsraven]

most of the time those braided hoses have a teflon inner hose, which means they are subject to damage from kinking etc, and also heat.
I suggest to drain the tank through the hose at the pump, then take the fitting off below the tank and install a petcock there for future considerations. it looks like a compression fitting was used there onb the original line coming through the floor. just ensure the petcock has a bore through size that is greater than or equal to the inside diameter of the hose etc for flow reasons. that will give you a chance to get anything out of the tank that may be in there as well plus check the hoses and fittings etc. if it were me I would also really check the fitting bore on the pump for poor threads as well as the fittings, maybe even take the pump off and chase the threads/clean the bores after so the cuttings don't get inside-or replace the pump. then use some pipe dope on the pipe threads upon installation. the AN fittings shouldn't need anything because it is the tapered seats that seal on each other, not the threads. (check the seats on the fittings male and female parts for cracks and or other issues, they should be smooth).

[NeoJuice]

After doing some digging through some receipt's I found the adapter size is 9/16"-18 that comes straight off the tank.

Problem is on the other end near the fuel pump the braided line has a metal 90 degree bend and seems to reduce down in size. I don't know what size that is.

So I know the fitting I'll need will be 3/8" NPT for the fuel pump side but not sure of the other line size b/c it sure does not look like 9/16"-18 (yellow arrow) or is the fitting 3/8" NPT 6AN that would connect to the yellow arrow?

I know its hard to tell from pictures but I'll have to physically take a look. Then I'm still stuck with the issue of getting the line plugged or draining the tank.

[_Ogre]

Originally Posted by NeoJuice

Then I'm still stuck with the issue of getting the line plugged or draining the tank.

don't mess around, just drain it. things can go south in a hurry when gas is involved

[NeoJuice]

True.

[dsraven]

is the fitting on the end of the tank bib threaded onto the bib or is that a compression fitting?
here is a wikipedia link for AN fitting sizes and how it all works
https://en.wikipedia.org/wiki/AN_thread

9/16-18 would be the threaded adapter part and usually has an O ring on it opposite the AN end. the AN fitting is usually classified as a number relating to 1/16 of an inch, so a #6 AN would be 6 x 1/16 which breaks down to 3/8. that is even a bit hard to understand because the different AN fittings can be classified as per wall thickness of the tubing it is used for, not like a bolt size.
I would have to say the fitting coming off the pump is likely a 1/4" npt (red arrow)

https://www.speedwaymotors.com/Small...BoCtfsQAvD_BwE

and the hose connected to that looks like a 6AN fitting (yellow arrow) but you may be able to check that by the wrench size (not always).

https://www.dragstuff.com/techarticl...nce-Chart.html

when you get that end apart I would see what size of hole is in the actual fittings where the fuel goes through just to ensure you will have ample fuel flow.

the white arrow is a bit of a guess because there is not good pic that shows the whole thing and the description is kinda off compared to the pic. maybe the PO threaded the inside of the 6ANx 9/16-18 adapter fitting so the tank bib tube would screw inside and the AN end of the fitting would connect to the hose. that's why I asked if it is a compression fitting onto the bib tube or if the bib is screwed into the end of the adapter fitting.

https://www.speedwaymotors.com/Hydra...ht,342357.html

either way, the bib tube needs to be supported for the added weight that the new hose and fittings will add. work fatigue on that bib, from vibration, could cause stress cracks and the bib could break off and burn your truck down if it doesn't have good support. especially if you add a petcock. that system has got to weigh more than the simple rubber hose that went to the steel line on the original frame, even if it had an inline fuel filter attached.
anyway, hope that helps and not confuses you

[NeoJuice]

Originally Posted by dsraven

is the fitting on the end of the tank bib threaded onto the bib or is that a compression fitting?
here is a wikipedia link for AN fitting sizes and how it all works
https://en.wikipedia.org/wiki/AN_thread

9/16-18 would be the threaded adapter part and usually has an O ring on it opposite the AN end. the AN fitting is usually classified as a number relating to 1/16 of an inch, so a #6 AN would be 6 x 1/16 which breaks down to 3/8. that is even a bit hard to understand because the different AN fittings can be classified as per wall thickness of the tubing it is used for, not like a bolt size.
I would have to say the fitting coming off the pump is likely a 1/4" npt (red arrow)

https://www.speedwaymotors.com/Small...BoCtfsQAvD_BwE

and the hose connected to that looks like a 6AN fitting (yellow arrow) but you may be able to check that by the wrench size (not always).

https://www.dragstuff.com/techarticl...nce-Chart.html

when you get that end apart I would see what size of hole is in the actual fittings where the fuel goes through just to ensure you will have ample fuel flow.

the white arrow is a bit of a guess because there is not good pic that shows the whole thing and the description is kinda off compared to the pic. maybe the PO threaded the inside of the 6ANx 9/16-18 adapter fitting so the tank bib tube would screw inside and the AN end of the fitting would connect to the hose. that's why I asked if it is a compression fitting onto the bib tube or if the bib is screwed into the end of the adapter fitting.

https://www.speedwaymotors.com/Hydra...ht,342357.html

either way, the bib tube needs to be supported for the added weight that the new hose and fittings will add. work fatigue on that bib, from vibration, could cause stress cracks and the bib could break off and burn your truck down if it doesn't have good support. especially if you add a petcock. that system has got to weigh more than the simple rubber hose that went to the steel line on the original frame, even if it had an inline fuel filter attached.
anyway, hope that helps and not confuses you

Dsraven,

As I've said before you are a wealth of knowledge and I appreciate your input and feedback and your time. I've read through your post a couple times and I think I understand now. To answer your questions see below.

-The bib from the tank is threaded into the 'bushing' (P2) then that is threaded into the 90 degree pipe(P1 to P). The 'T' thread on the end of the pipe is listed in the picture as 9/16-18 which is 6AN, which the other end of my inlet fuel line is connected to under the truck.

I was at gregs distributors are lunch and talked with the hose/brake guy there he said 99.9% of the time the hose ends are the same. I picked up a new anodized 3/8" NPT to 6AN fitting which should work for the fuel pump. I also picked up some thread sealant he recommended. I'll put it on the threads to let dry until I can do the install.

-The edelbrock 1721 fuel pump as 3/8" NPT female fittings for both inlet and outlet.

-I've got the line attached and supported good with cushion clamps along the frame up to the front of the motor.

[dsraven]

sounds like you have it figured.
the AN fittings use the outside diameter of the tubing for a size, I believe, and not all tubing is the same wall thickness (schedule) thats where it gets confusing.
hopefully you don't have to buy a new pump to fix the leak.
still have those heaters, by the way, if you need one.

[NeoJuice]

Originally Posted by dsraven

sounds like you have it figured.
the AN fittings use the outside diameter of the tubing for a size, I believe, and not all tubing is the same wall thickness (schedule) thats where it gets confusing.
hopefully you don't have to buy a new pump to fix the leak.
still have those heaters, by the way, if you need one.

Yes I still haven't forgot about the heaters I'll keep the thread updated after I replace the fitting and see what happens. I suspect a new fitting with some thread sealant should do the trick. If not I'll be really pissed lol.

[mr48chev]

You are probably going to end up draining the tank and removing the whole braided line to be able to correctly match up the fitting as it may have the wrong fitting if the leak is between the adapter and the female end of the line.

You also need to go to someone who is knowledgeable in the fittings such as the local to you Aeroquip dealer.

[NeoJuice]

The leak is where the red arrows are in the pictures shown above on the fuel pump 3/8" NPT inlet and the adapter. There is no leak on the AN braided line side that goes toward the pump.

[dsraven]

try these guys if you get stuck. I have had great luck here in Calgary. they also make brake lines, oil cooler hoses etc. they have an online catalogue as well.


Green Line Edmonton
7003 Roper Road
Edmonton, AB T6B3K3
(780) 465-5216
(800) 267-2572
Mon - Fri 7:30 am - 5:00 pm
Saturday 9:00 AM to 1:00 PM

[dsraven]

seems like you have a bad fitting or someone overtightened it and cracked the pump housing a bit. npt is tapered so the more it is tightened the more chance somethins gonna give.

[mr48chev]

Originally Posted by dsraven

seems like you have a bad fitting or someone overtightened it and cracked the pump housing a bit. npt is tapered so the more it is tightened the more chance somethins gonna give.

As he usually does Dsraven came up with some real good things to check. First being previous owner damage. Second being the wrong fitting for the pump. You know what it takes because you checked while doing your homework but is the fitting they used a npt thread?

Every time I assume that the guy I am following behind did things correctly it bites a chunk right out of my tail feathers. If I don't assume and just take it apart and start investigating I usually figure it out pretty quick. That from about 35 years of having stuff brought to me that someone else worked on and it didn't work so I ended up with it to straighten out.

[NeoJuice]

Thanks for the input guys. As soon as I have a chance to get the fitting replaced I will update the thread.

[NeoJuice]

Didn't end up loosing to much gas at all. I removed the line and put my thumb over the inlet hose. Not much came out of the pump itself. Screwed in the new fitting and snugged it up and no leaks in the last 24 hours.

As I mentioned before I picked up a anodized 3/8" NPT to 6AN fitting and put the permatex on it 24hrs before hand so that i know it was dry.

[mr48chev]

Good to see that you have it solved.

[dsraven]

good you got it figured out.
sure seems like a lot of lines in one area. is it fuel lines and trans cooler tubing there plus a wiring harness?

[NeoJuice]

Yes the two fuel and trans cooler lines with a set of wiring coming from the battery for the fan relay.