Two metal lines running up the back of the cab on passenger side? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**IT Cowboy** · 02-08-2025, 06:59 PM

I have two lines going from the top of the fuel tank on the passenger side and up the back the cab corner. What are these and where do they go. The lines are held in place with a small bolt clip on the corner of the cab right by the top of the seat. The line were rattling a but against the back of the cab pillar as there is a bit of play in them. I shoved a piece of closed cell foam up there so they cannot rattle.

**Steeveedee** · 02-08-2025, 07:27 PM

They are vapor recovery lines for the evaporated fuel from the tank. There is a vapor separator in the tank and a canister that the vapors adsorb onto the activated charcoal inside. Those fumes are drawn off and combusted when the truck is running. The canister was installed below the battery. Is it still there? It's black, about 6" in diameter and about 9 inches tall. Can you show us a pic? If it's there, also show how the lines connect to the engine.

**Classic Bowties** · 02-09-2025, 02:19 AM

p

Quote:

Originally Posted by Steeveedee

They are vapor recovery lines for the evaporated fuel from the tank. There is a vapor separator in the tank and a canister that the vapors adsorb onto the activated charcoal inside. Those fumes are drawn off and combusted when the truck is running. The canister was installed below the battery. Is it still there? It's black, about 6" in diameter and about 9 inches tall. Can you show us a pic? If it's there, also show how the lines connect to the engine.

^ ^ ^ IT Cowboy, here are a few id pictures from our old saved folder archives to go with Steeveedee's above reply, the below pictured pass side fender mounted EEC system fuel vapor canister and mounting bracket setup was removed from a 72 C/10 BBC 402 truck. Mel

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**IT Cowboy** · 02-08-2025, 07:52 PM

I will need to look close tomorrow. I am curious if they run across the top of the cab or how they get to the canister. I see the two lines going up inside the back and that is it. I have a slight gas small in the cab but I suspect it is a poor vent on the fuel cap as the seal inside is all dried out.

**Steeveedee** · 02-08-2025, 08:49 PM

There should be a hose from a nipple on the tank to one of those tubes, and a hose leading to the vapor canister. It has a metal line for part of the run from there to the canister, with hoses at each end.

**IT Cowboy** · 02-08-2025, 09:02 PM

Quote:

Originally Posted by Steeveedee

There should be a hose from a nipple on the tank to one of those tubes, and a hose leading to the vapor canister. It has a metal line for part of the run from there to the canister, with hoses at each end.

Yup, I see those. I see where the lines go up but I do not see that they come down so they must run down to the frame on the inside of the metal on the back of the B pilar

**Classic Bowties** · 02-09-2025, 12:31 AM

Quote:

Originally Posted by IT Cowboy

I have a slight gas small in the cab but I suspect it is a poor vent on the fuel cap as the seal inside is all dried out.

IT Cowboy, if you are working on a 1972 EEC model with the under hood OE vapor canister setup, your fuel cap would not be a vented style fuel cap. All original 72 pickup truck, blazer and suburban models equipped with the EEC fuel tank systems used a pressure vacuum (non-vented) gas cap, by design the EEC fuel tank doesn't vent through the filler cap on 72 EEC equipped models. If working on a deserving build and want the correct style non-vented 72 fuel filler cap, we have both 72 specific GM NOS stainless or NOS painted/primed styles of the double ring "pressure vacuum" EEC gas caps available for purchase in the below linked long running parts board f/s thread. Have a look and let us know if interested, Mel

http://67-72chevytrucks.com/vboard/s...d.php?t=837726

.

**71CHEVYSHORTBED402** · 02-08-2025, 10:10 PM

Looks like

**IT Cowboy** · 02-08-2025, 10:17 PM

Quote:

Originally Posted by 71CHEVYSHORTBED402

Looks like

OK that makes more sense now

**IT Cowboy** · 02-09-2025, 02:27 AM

Thank you! So I possibly have the wrong cap and it is supposed to seal. I will do some more checking tomorrow

**Steeveedee** · 02-09-2025, 11:11 AM

Check if those pipes are blocked off. In your firewall graffiti thread, I don't see any lines from the canister to the engine. One line is for vacuum so that the valve on the canister opens when the engine is running. That's 3/16", I think. The hose for the vapors is 3/8" I think, and either went to the bottom of the air cleaner or into the PCV hose. Non-stock air cleaner and PCV hose going directly to the carburetor means it's likely that the system is disconnected. If so, you will need a vented cap.

02-08-2025, 06:59 PM	#1
IT Cowboy Active Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 140	Two metal lines running up the back of the cab on passenger side? I have two lines going from the top of the fuel tank on the passenger side and up the back the cab corner. What are these and where do they go. The lines are held in place with a small bolt clip on the corner of the cab right by the top of the seat. The line were rattling a but against the back of the cab pillar as there is a bit of play in them. I shoved a piece of closed cell foam up there so they cannot rattle. __________________ '72 C10 / 402 ___________________________________________ Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

02-08-2025, 07:27 PM	#2
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,841	Re: Two metal lines running up the back of the cab on passenger side? They are vapor recovery lines for the evaporated fuel from the tank. There is a vapor separator in the tank and a canister that the vapors adsorb onto the activated charcoal inside. Those fumes are drawn off and combusted when the truck is running. The canister was installed below the battery. Is it still there? It's black, about 6" in diameter and about 9 inches tall. Can you show us a pic? If it's there, also show how the lines connect to the engine. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

02-08-2025, 07:52 PM	#4
IT Cowboy Active Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 140	Re: Two metal lines running up the back of the cab on passenger side? I will need to look close tomorrow. I am curious if they run across the top of the cab or how they get to the canister. I see the two lines going up inside the back and that is it. I have a slight gas small in the cab but I suspect it is a poor vent on the fuel cap as the seal inside is all dried out. __________________ '72 C10 / 402 ___________________________________________ Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

02-08-2025, 08:49 PM	#5
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,841	Re: Two metal lines running up the back of the cab on passenger side? There should be a hose from a nipple on the tank to one of those tubes, and a hose leading to the vapor canister. It has a metal line for part of the run from there to the canister, with hoses at each end. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

02-08-2025, 10:10 PM	#8
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,370	Re: Two metal lines running up the back of the cab on passenger side? Looks like Attached Images __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assembly guide (kit) for restoring this truck from the ground up, complete with details including full hardware descriptions. Much of the info. applies to all 67-72 GM. My build thread, with some info. about the assembly kit https://67-72chevytrucks.com/vboard/...d.php?t=730025

02-09-2025, 02:27 AM	#10
IT Cowboy Active Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 140	Re: Two metal lines running up the back of the cab on passenger side? Thank you! So I possibly have the wrong cap and it is supposed to seal. I will do some more checking tomorrow __________________ '72 C10 / 402 ___________________________________________ Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

02-09-2025, 11:11 AM	#11
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,841	Re: Two metal lines running up the back of the cab on passenger side? Check if those pipes are blocked off. In your firewall graffiti thread, I don't see any lines from the canister to the engine. One line is for vacuum so that the valve on the canister opens when the engine is running. That's 3/16", I think. The hose for the vapors is 3/8" I think, and either went to the bottom of the air cleaner or into the PCV hose. Non-stock air cleaner and PCV hose going directly to the carburetor means it's likely that the system is disconnected. If so, you will need a vented cap. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

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