Fuel Tank 5/16 inch Vent Line

[Melbo]

I have removed my fuel tanks and coated them with epoxy. I am in the process of installing steel lines and was looking at previous posts and the
service manual. I see in the manual and photos from previous posts that the small vent line on the front tank ( not the one with the fuel pick up and
sending unit ) goes towards the passenger side and around the back of the rear tank and then to the vapor separator at the drivers side wheel well.
Is there any good reason that it can not make a more direct path to the separator by making a loop on top of the tank and then connecting to the rear
tank vent line and the separator? If there is something I am missing or should do differently please let me learn from your experience. If there is
no good reason for the round about way I will make a shorter path and connect them together per the diagram for the vapor separator. I also remember
something about making the connection between the lines up high by the separator. Any information to keep me from doing it over is appreciated.

Thank You

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC

 

[Matt Colie]

> I have removed my fuel tanks and coated them with epoxy. I am in the process of installing steel lines and was looking at previous posts and the
> service manual. I see in the manual and photos from previous posts that the small vent line on the front tank ( not the one with the fuel pick up
> and sending unit ) goes towards the passenger side and around the back of the rear tank and then to the vapor separator at the drivers side wheel
> well. Is there any good reason that it can not make a more direct path to the separator by making a loop on top of the tank and then connecting to
> the rear tank vent line and the separator? If there is something I am missing or should do differently please let me learn from your experience.
> If there is no good reason for the round about way I will make a shorter path and connect them together per the diagram for the vapor separator. I
> also remember something about making the connection between the lines up high by the separator. Any information to keep me from doing it over is
> appreciated.
>
> Thank You
>
> Melbo

Melbo,

That line is a vapor vent to relieve the static pressure in the tanks. In the older coaches (Like mine) it does not take the route you have
described. Mine come over to the frame rail by the separator and join there to go to the vapor valve. If later coaches did it differently, I suspect
that there might have been some reason.

What you are probably also remembering is my writing about moving the junction of the fill vent (the other line that comes out of the sender) so the
full rear (main) tank does not interfere with the venting of the auxiliary (front) tank. This make a huge difference when fueling. It a mod that I
highly suggest. Do a search here for "Recommending High T".

I hope that is the answers you were looking for, if not, try again....

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[Ken H.]

Melbo,

I agree with Matt: There's no reason to take a circuitous route for the
vent line. On my '76, the one from each tank takes the most direct route,
following grooves in the tops of the tanks, to the left wheel well and up a
few inches toward the liquid-vapor separator. There, they're tee'd
together for the single line into the separator.

Ken H.

> I have removed my fuel tanks and coated them with epoxy. I am in the
> process of installing steel lines and was looking at previous posts and the
> service manual. I see in the manual and photos from previous posts that
> the small vent line on the front tank ( not the one with the fuel pick up
> and
> sending unit ) goes towards the passenger side and around the back of the
> rear tank and then to the vapor separator at the drivers side wheel well.
> Is there any good reason that it can not make a more direct path to the
> separator by making a loop on top of the tank and then connecting to the
> rear
> tank vent line and the separator? If there is something I am missing or
> should do differently please let me learn from your experience. If there is
> no good reason for the round about way I will make a shorter path and
> connect them together per the diagram for the vapor separator. I also
> remember
> something about making the connection between the lines up high by the
> separator. Any information to keep me from doing it over is appreciated.
>
> Thank You
>
> Melbo
> --
> Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Melbo]

Thank You for the responses

Saved me a lot of work

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC

 

[Jim Hupy]

Be sure that the vent lines do not have low spots or get pinched by the
tanks on their way to the fuel/vapor separator or the charcoal canister.
Same for the tank "burp" lines that terminate at the filler neck.
Jim Hupy

> Thank You for the responses
>
> Saved me a lot of work
>
> Melbo
> --
> Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[jim kanomata1]

Be sure to follow Jim H's suggestion and specially on the 1/2" vent hose at
the filler neck.
Be sure and replace the selector valve and fuel pump if it ha not been done
in the last 5 years.

> Be sure that the vent lines do not have low spots or get pinched by the
> tanks on their way to the fuel/vapor separator or the charcoal canister.
> Same for the tank "burp" lines that terminate at the filler neck.
> Jim Hupy
>

>
> > Thank You for the responses
> >
> > Saved me a lot of work
> >
> > Melbo
> > --
> > Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[powwerjon]

Here is an album that shows how I did the redo of the fuel tanks.

http://www.gmcmhphotos.com/photos/g6928-fuel-tank-system-rebuild.html

JR Wright
GMC GreatLaker
GMCMI
GMC Eastern States
Michigan
On Location inTucson

>
> Be sure to follow Jim H's suggestion and specially on the 1/2" vent hose at
> the filler neck.
> Be sure and replace the selector valve and fuel pump if it ha not been done
> in the last 5 years.
>
>

>
>> Be sure that the vent lines do not have low spots or get pinched by the
>> tanks on their way to the fuel/vapor separator or the charcoal canister.
>> Same for the tank "burp" lines that terminate at the filler neck.
>> Jim Hupy
>>

>>
>>> Thank You for the responses
>>>
>>> Saved me a lot of work
>>>
>>> Melbo
>>> --
>>> Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[Carl Stouffer]

I put mine back in, pretty much the same as they came out:

http://www.gmcmhphotos.com/photos/mechanical/p34775-gas-tank-clean-up-2ffuel-line-replacement.html

Hope the rest of the album is helpful too.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member

 

[Jim Hupy]

Just a reminder that " the toughest chain is ONLY as strong as it's weakest
link. In this case, it is the coupling between the tank lines and the metal
fuel and vent lines. Do not join them with short pieces of hose and clamps.
Remove the senders from the tanks, replace the o rings while you are at it,
cut off the bubble ends and replace with either ferrules and compression
nuts, or flared fittings. You might also consider in-tank fuel pumps like
some have done. Not my favorite choice, but many have used them with good
reliability. There is no "once and done forever" with mechanical systems.
The perfect system has no electrical connections nor moving parts. An
anvil is an example, but, they don't pump fuel.
Jim Hupy

> I put mine back in, pretty much the same as they came out:
>
>
> http://www.gmcmhphotos.com/photos/mechanical/p34775-gas-tank-clean-up-2ffuel-line-replacement.html
>
> Hope the rest of the album is helpful too.
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Melbo]

I am using brass compression fittings on the 3/8 inch 5/16 inch and 1/4 inch lines. I am going to pressure test the fittings with air and soapy water
before the tanks are reinstalled. I plan to glue rubber blocks ( like the ones under air conditioner condensors ) as a precaution on both sides of
the 5/16 inch vent lines because of the slight upwards slant so they don't get squeezed between the floor and the tank. I replaced and tested the
fuel gauge sending units and replaced the "o" ring on the pick up - sending unit. I was measuring under the coach today and noticed that the filler
pipes are rusty looking and wondered if I should also remove them and coat them with epoxy before I wrap up this fuel system portion of the project or
if they are usually fine left alone. It would be much easier with the extra working room to do it now. Any opinions about the filler tubes is
appreciated.

Thanks

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC

 

[powwerjon]

Not necessarily is the hose the weak link, can be your worst enemy if you use a cheap hose! I used the Gates Barricade® fuel injection hose which is a low-permeation, multi-fuel compatible hose with 5-layer GreenShield™ barrier technology used in its manufacture. It exceeds the requirements of SAE J30R14T2. It is actually a higher pressure for fuel injection, but for short pieces, I bought only about 5 foot to complete the junctions. For rest of the hose pieces that I used in the rest of the fuel system a Goodyear SAE J30R9 fuel which is 4 layer hose with a nitrile inner liner. Theses hoses should be a one time fix. The bullet proof method is the use of swagelok or parker tubing connectors for a mechanical connection between the 2 tubing sections such as Emery has used in his fuel system. I recommend brass over stainless steel fittings.

Goodyear R9 hose:

https://goodyearrubberproducts.com/2012pdfs/Goodyear_Commercial_Truck_Belts_and_Parts/files/assets/downloads/page0032.pdf

Gates Hose:

https://ww2.gates.com/europe/downloads/download_common.cfm?file=70517_E2_BARRICADE_BROCHURE.pdf&folder=brochure&location_id=19079

Parker catalog: https://www.parker.com/literature/Tube%20Fittings%20Division/4300_Catalog_Cover.pd

Sweglok Catalog: https://www.swagelok.com/en/product/Fittings/Tube-Fittings-and-Tube-Adapters

This is how I have done it with very good results, your choices may vary.

JR Wright
GMC GreatLaker
GMCGL Tech Editor
GMCMI
GMC Eastern States
Michigan
On Location inTucson

>
>
> Just a reminder that " the toughest chain is ONLY as strong as it's weakest
> link. In this case, it is the coupling between the tank lines and the metal
> fuel and vent lines. Do not join them with short pieces of hose and clamps.
> Remove the senders from the tanks, replace the o rings while you are at it,
> cut off the bubble ends and replace with either ferrules and compression
> nuts, or flared fittings. You might also consider in-tank fuel pumps like
> some have done. Not my favorite choice, but many have used them with good
> reliability. There is no "once and done forever" with mechanical systems.
> The perfect system has no electrical connections nor moving parts. An
> anvil is an example, but, they don't pump fuel.
> Jim Hupy
>

>
>> I put mine back in, pretty much the same as they came out:
>>
>>
>> http://www.gmcmhphotos.com/photos/mechanical/p34775-gas-tank-clean-up-2ffuel-line-replacement.html
>>
>> Hope the rest of the album is helpful too.
>> --
>> Carl Stouffer
>> '75 ex Palm Beach
>> Tucson, AZ.
>> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
>> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
>> Eagles,
>> Solar battery charging. GMCSJ and GMCMI member
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[jim kanomata1]

Melbo,
There is a reason why compression fittings are not used much in the
automotive industry.
As a 12 year old boy working on my Mothers car, found out the compression
fitting was not a very reliable fitting.
DOT fittings are reliable as the tubing has a SS built in insert to keep
the tubing from collapsing.
The flaired fittings are the most reliable.

> I am using brass compression fittings on the 3/8 inch 5/16 inch and 1/4
> inch lines. I am going to pressure test the fittings with air and soapy
> water
> before the tanks are reinstalled. I plan to glue rubber blocks ( like the
> ones under air conditioner condensors ) as a precaution on both sides of
> the 5/16 inch vent lines because of the slight upwards slant so they don't
> get squeezed between the floor and the tank. I replaced and tested the
> fuel gauge sending units and replaced the "o" ring on the pick up -
> sending unit. I was measuring under the coach today and noticed that the
> filler
> pipes are rusty looking and wondered if I should also remove them and coat
> them with epoxy before I wrap up this fuel system portion of the project or
> if they are usually fine left alone. It would be much easier with the
> extra working room to do it now. Any opinions about the filler tubes is
> appreciated.
>
> Thanks
>
> Melbo
> --
> Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[john shutzbaugh]

"anvil" Made me laugh James.

John S.
--
John Shutzbaugh, Vacaville, CA, ncserv;
77 Eleganza, bought it new, can't blame PO, and
78 Buskirk stretch, "What were we thinking?"