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-   -   Fuel system hose sizes? (https://67-72chevytrucks.com/vboard/showthread.php?t=863001)

r8rs4lf 03-02-2026 02:37 PM
Fuel system hose sizes?
 
2 Attachment(s)
I went under my truck to check a few things out and saw the rubber fuel system hoses that route from the gas tank, into the pillar and under the truck are cracked.

Anyone know the size(s) off hand and would this affect a gas smell in the cab?

LS short box 03-02-2026 05:46 PM
Re: Fuel system hose sizes?
 
That looks very scary. Replace ASAP!

PbFut 03-02-2026 08:29 PM
Re: Fuel system hose sizes?
 
I am struggling to understand what I am seeing relative to routing in the photo. The fuel supply and return lines are relatively flat from the bottom of cab to the pump. If equipped with tank vent and charcoal canister, that line is mostly a vapor path so you may not get much dripping but will produce noticable fumes and they are quit flammable. My truck not equipped with a canister but i have ssen post talking about a loop up into the B pillar, i assume to avoid raw fuel from flowing and possibly rollover protection. I would change out the cracked hose ASAP. A check of the canister is in order as well.

Steeveedee 03-02-2026 10:23 PM
Re: Fuel system hose sizes?
 
5/16"

RustyPile 03-02-2026 10:36 PM
Re: Fuel system hose sizes?
 
Depending on the delivery and emissions systems, and engine on your truck, the size may vary.. But the size is easy to determine.. Simply measuring the O.D. of the metal tube will determine the size needed.

One of these should be in every tool box..
https://www.bing.com/search?qs=AS&pq...ANAB01&PC=LCTS

Steeveedee 03-02-2026 11:18 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by RustyPile (Post 9424912)
Depending on the delivery and emissions systems, and engine on your truck, the size may vary.. But the size is easy to determine.. Simply measuring the O.D. of the metal tube will determine the size needed.

One of these should be in every tool box..
https://www.bing.com/search?qs=AS&pq...ANAB01&PC=LCTS
Yup, but the vent lines were always 5/16", iirc. The other line looks to be 3/8", for fuel to the pump. I could be wrong...been known to happen...and everyone should have dial or vernier calipers.

r8rs4lf 03-03-2026 10:56 AM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by PbFut (Post 9424890)
I am struggling to understand what I am seeing relative to routing in the photo. First of all the pics are upside down so that makes it hard. :lol: I believe those are vent lines that are cracked. I don't believe those are the fuel lines as there is a hard line with a small piece of rubber line with clamps (pic #2) attached to another hard line that I'm assuming goes towards the gas tank.

The fuel supply and return lines are relatively flat from the bottom of cab to the pump. If equipped with tank vent and charcoal canister, that line is mostly a vapor path so you may not get much dripping but will produce noticable fumes and they are quit flammable. I recently changed out my fuel pump and it had three ports. One from the tank, one to the carb, and a vent line that goes towards the rear of the truck. Doing some research I have the ECC system which makes sense because this was a Fremont California built truck.

My truck not equipped with a canister but i have ssen post talking about a loop up into the B pillar, i assume to avoid raw fuel from flowing and possibly rollover protection. I don't have a canister either, but I do have the vent line running up the B pillar and through the floorboard. That is what you are seeing underneath the truck.

I would change out the cracked hose ASAP. A check of the canister is in order as well.
Today or tomorrow I will change them out as I'm waiting for other parts for my transmission and plan to knock it all out at the same time.

r8rs4lf 03-03-2026 11:03 AM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by Steeveedee (Post 9424910)
5/16"
Quote:
Originally Posted by Steeveedee (Post 9424919)
Yup, but the vent lines were always 5/16", iirc. The other line looks to be 3/8", for fuel to the pump. I could be wrong...been known to happen...and everyone should have dial or vernier calipers.
Thanks, I will go get that today.

There should not be any fuel in those lines right? Also, would those cracked lines under the truck contribute to a fuel smell in the cab?

I have not looked at my gas tank or the lines behind the seat yet. I do notice a fuel smell when I have filled up the tank so I don't do that anymore.

pjmoreland 03-03-2026 12:49 PM
Re: Fuel system hose sizes?
 
An EEC tank will have some rubber lines attached to it that could be cracked. There is a short section that runs from the filler neck to the top of the tank. Then there is another one that connects the tank to the line that loops up into the rear passenger pillar.

If you installed a fuel pump that has three attachment ports, and you attached the return port to the vent line, then the pump will be sending fuel back up the vent line to the tank, which is not its original purpose. The tank will have no way to vent excess pressure in this scenario.

r8rs4lf 03-03-2026 03:56 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by pjmoreland (Post 9424978)
An EEC tank will have some rubber lines attached to it that could be cracked. There is a short section that runs from the filler neck to the top of the tank. I replaced that.

Then there is another one that connects the tank to the line that loops up into the rear passenger pillar. There are actually two lines on the passenger side, both with small pieces of rubber hose connecting the hard lines. You can see HERE! Post 27

If you installed a fuel pump that has three attachment ports, and you attached the return port to the vent line, then the pump will be sending fuel back up the vent line to the tank, which is not its original purpose. The tank will have no way to vent excess pressure in this scenario. When I replaced the fuel pump I attached the lines exactly the way they came off. I think where I'm getting confused is the vent line going up front hooks up to a canister that is no longer there. I thought the third port on the pump was a vent line, but it was the return line to the tank. I cannot find the line that goes to the canister as of yet. I'm assuming it's just hanging somewhere. I read in that same post above to just connect to a filter.
I'm going to replace all those old rubber hoses underneath. I'm assuming one of them is the return line with the others being the vent line.

pjmoreland 03-03-2026 04:07 PM
Re: Fuel system hose sizes?
 
The vent line runs along the frame rail right next to the fuel supply line. The vent line extends further to the front of the frame rail though, and it curls around the top of the frame rail and points toward the battery. A rubber hose would attach to it there and would run over to the canister in the front of the fender next to the battery. Do you have two or three steel fuel lines going through the floor of your cab?

https://67-72chevytrucks.com/vboard/...1&d=1736647953

IT Cowboy 03-03-2026 04:48 PM
Re: Fuel system hose sizes?
 
5/16
3/8

I replaced mine with Gates Barricade 30R14 which is ethanol proof. It was probably overkill but I wanted to be sure it lasts a while.

58 Special 03-03-2026 04:58 PM
Re: Fuel system hose sizes?
 
I think only 1972 have the canister in front. all others are vented through the cap.
If I'm wrong I will be corrected. I'm used to it.

71CHEVYSHORTBED402 03-03-2026 06:30 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by 58 Special (Post 9425015)
I think only 1972 have the canister in front. all others are vented through the cap.
If I'm wrong I will be corrected. I'm used to it.
Well.............:lol:;)

Barring situations the factory isn't using up former stock or moving onto new materials, identified by "ish" - I'm pretty sure the 1970ish-1971 cap only vents when there's high pressure in the system, where the canister isn't cutting it, while the 1972ish cap vents more often under less pressure.

The cannisters were installed in 1970ish ending I don't know, 1980s?

I wonder how old tanks vented, 1970ish and before? I assume the caps.

Reading above, I didn't know the old hoses may not be ethanol proof. - Personally my 71 truck has EEC/Fuel hoses that came with these trucks, but I installed a regular fuel hose from the hardline to the fuel pump. I only use ethanol free fuel, so far no problems since the restoration, without a fuel return line the factory began installing with certain transmissions, beginning 1972-ish. My 400TH is one of those transmissions.

IT Cowboy 03-03-2026 06:39 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by 71CHEVYSHORTBED402 (Post 9425035)
Well.............:lol:;)

Barring situations the factory isn't using up former stock or moving onto new materials, identified by "ish" - I'm pretty sure the 1970ish-1971 cap only vents when there's high pressure in the system, where the canister isn't cutting it, while the 1972ish cap vents more often under less pressure.

The cannisters were installed in 1970ish ending I don't know, 1980s?

I wonder how old tanks vented, 1970ish and before? I assume the caps.

Reading above, I didn't know the old hoses may not be ethanol proof. - Personally my 71 truck has EEC/Fuel hoses that came with these trucks, but I installed a regular fuel hose from the hardline to the fuel pump. I only use ethanol free fuel, so far no problems since the restoration, without a fuel return line the factory began installing with certain transmissions, beginning 1972-ish. My 400TH is one of those transmissions.

I have a 72 Highlander with the 400 ci and the TH400 and it has the return fuel line and the evap canister

r8rs4lf 03-03-2026 09:36 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by pjmoreland (Post 9425006)
The vent line runs along the frame rail right next to the fuel supply line. The vent line extends further to the front of the frame rail though, and it curls around the top of the frame rail and points toward the battery. A rubber hose would attach to it there and would run over to the canister in the front of the fender next to the battery. Do you have two or three steel fuel lines going through the floor of your cab? I have three lines. I found the vent line up front. It was hiding in the frame. Someone took the canister out, left the line hanging, added a rubber piece to the end and put a bolt in it. In that pic, it's the line pointing to the left with that spring wrapped around it correct? Truck runs like a champ so it must not be affected by that. I read about adding some type of filter to the end.
So I finished replacing the rubber hose from the filler to the tank, both rubber lines on the passenger (EEC) side that go up the B pillar, the rubber hose underneath connecting the hard line tank feed to the hard line in the frame (remember this), the rubber hose connecting the hard return fuel line from the pump to the hard line underneath back to the tank, and the vent hard line that goes from inside the cab through the floor connected by a long(er) piece of rubber hose to the vent line in the frame. WHEW!!! That was a mouthful!

PROBLEM!!!!

I went to start it to check for leaks and there was one from the tank hard line fuel feed (^^^remember???) that goes through the floor. That line when it goes under the floor, there is a bend that shoots it towards the passenger frame rail. Well, where that line bends, apparently it's been rubbing for quite some time against the carrier cross member and made a small cut in the line. I guess moving the line a bit while attaching that rubber hose to connect it to the frame rail line irritated it enough to start a pinhole leak. FML!!! Anyone else have this kind of luck I do?

Now I need to head to Classic Industries tomorrow to find that line.

IT Cowboy 03-03-2026 09:41 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by r8rs4lf (Post 9425065)
So I finished replacing the rubber hose from the filler to the tank, both rubber lines on the passenger (EEC) side that go up the B pillar, the rubber hose underneath connecting the hard line tank feed to the hard line in the frame (remember this), the rubber hose connecting the hard return fuel line from the pump to the hard line underneath back to the tank, and the vent hard line that goes from inside the cab through the floor connected by a long(er) piece of rubber hose to the vent line in the frame. WHEW!!! That was a mouthful!

PROBLEM!!!!

I went to start it to check for leaks and there was one from the tank hard line fuel feed (^^^remember???) that goes through the floor. That line when it goes under the floor, there is a bend that shoots it towards the passenger frame rail. Well, where that line bends, apparently it's been rubbing for quite some time against the carrier cross member and made a small cut in the line. I guess moving the line a bit while attaching that rubber hose to connect it to the frame rail line irritated it enough to start a pinhole leak. FML!!! Anyone else have this kind of luck I do?

Now I need to head to Classic Industries tomorrow to find that line.
It is mostly out of site so you could get some line and bend it yourself and flare it if the line from CI is crazy expensive

Loose Screw 03-04-2026 06:17 AM
Re: Fuel system hose sizes?
 
5/16
aaaand after learning how to do A/N PTFE I won't ever use rubber fuel line again....steel line is great but you do need some flex tank to frame and frame to pump. Using PTFE I eliminated those rubber flex jumpers...

r8rs4lf 03-05-2026 02:05 PM
Re: Fuel system hose sizes?
 
Quote:
Originally Posted by IT Cowboy (Post 9425067)
It is mostly out of site so you could get some line and bend it yourself and flare it if the line from CI is crazy expensive
I just went ahead and placed an order with LMC for both lines, new sending unit, grommets, and filler neck gasket. Be here in about a week when I can address this again. YAY! :whine:

Now I'm thinking I should pull the tank now while waiting for parts and have it cleaned and lined so I won't have to deal with this again.


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