78 K10 Fuel filling secondary tank - The 1947 - Present Chevrolet & GMC Truck Message Board Network

masterlock · 09-19-2015, 03:38 PM

So I just picked up a 78 K10 today and the guy said that if you run the primary tank the truck runs fine but it also fills the second tank to the point that it overflows out of the fuel neck.
I assume and hope that it is the selector valve that is allowing this to happen but wanted you guys to weigh in before I go and start tearing stuff out of the truck.
Thanks

bmchevy1979 · 09-19-2015, 09:05 PM

The return lines to the selector may also be flipped assuming it's a 6port valve

masterlock · 09-24-2015, 08:29 PM

Ok so I figured out the problem and need some more advice. For some reason the return line to the primary tank is disconnected and it is routed into the second tank and it looks as though the return for the second tank is capped at the selector valve. Not sure what the genius behind that was thinking. Anyway I want to know what you guys think as far as options go. Im thinking remove the bed or drop the tanks or just take it to a mechanic and let him fix it. Which would you suggest I do???

Dead Parrot · 09-25-2015, 11:05 AM

If you have the space, tools and borrowable manpower, pull the bed. It is possible those are the original hoses and if so, they are EOL. Might be why the PO sold it. This way, you can replace all the hoses, check the tank ground wires, fix any cab corner rust issues, fix any bed rust issues and give the underside of the bed a good coat of paint/anti rust coating. For that matter, you could pull the senders out and do a visual inspection of the inside of the tanks.

Keith Seymore · 09-25-2015, 12:29 PM

Quote:

Originally Posted by Dead Parrot

If you have the space, tools and borrowable manpower, pull the bed. It is possible those are the original hoses and if so, they are EOL. Might be why the PO sold it. This way, you can replace all the hoses, check the tank ground wires, fix any cab corner rust issues, fix any bed rust issues and give the underside of the bed a good coat of paint/anti rust coating. For that matter, you could pull the senders out and do a visual inspection of the inside of the tanks.

Plus - you'd already be well on your way to a frame off restoration...

(lol)

Seriously, though: it doesn't take much to pop the bed off and it makes all this infinitely easier.

K

masterlock · 09-25-2015, 10:42 PM

Quote:

Originally Posted by Keith Seymore

Plus - you'd already be well on your way to a frame off restoration...

(lol)

Seriously, though: it doesn't take much to pop the bed off and it makes all this infinitely easier.

K

Yeah thats how my last truck started and its still not wired, "oh ill just pull the cab off" = full restoration. I would be divorced if I pull that one again.

Ok so I am gonna try and pull the bed tomorrow, Where is this wiring pigtail that I need to disconnect? Any pictures would be appreciated

tucsonjwt · 09-26-2015, 07:38 PM

The tail lights should have a round plug which disconnects near the rear bumper. Also, you might have a trailer plug (lights, brakes) which needs to be removed.

I think the vent hose from the differential also is bolted to the frame, so that needs to be disconnected.

Of course, the screws holding the filler necks to the bed need to be removed, and if you have a later truck style there may be a metal grounding strap connecting the necks to the frame (a 78 should not have them.)

You just need to crawl under the bed and look for anything that connects the bed to the frame.

The real problem with removing the bed is the bolts. It is very possible that the bolts are rusted in place and you may snap the bolts off or round out the square mounting holes in the bed floor. So, if the bolts are difficult to remove, it is best just to cut them off and replace the nuts and bolts with new ones. Pre-soaking with PB Blaster or equivalent for a few days is always a good idea.

If you don't have an engine hoist, you can jack the bed up with a bottle jack and 4x4s and support it with perpendicular doubled 2x4s on saw horses or stacked concrete blocks when it is high enough to clear the rear tires.

masterlock · 09-27-2015, 10:45 PM

Thanks tucsonjwt, yeah those bolts were a nightmare, I cut some from underneath and ground some down from the top. Then I realized that the reason that the fuel lines were all messed up was because the primary tank was leaking so using the angle grinder became a bit dangerous. So i figure I will just replace both tanks while I have the bed off. I assume that they are 20 gallon. Surprised they are so cheap...

Also anyone know what bolt sizes and lengths to get, the one that were in there are destroyed and LMC is smart enough to no list the sizes in the catalog. I would rather pay 2 bucks for a bolt than get them from LMC for 10 bucks

09-19-2015, 03:38 PM	#1
masterlock Registered User Join Date: Jul 2010 Location: San Diego, CA Posts: 281	78 K10 Fuel filling secondary tank So I just picked up a 78 K10 today and the guy said that if you run the primary tank the truck runs fine but it also fills the second tank to the point that it overflows out of the fuel neck. I assume and hope that it is the selector valve that is allowing this to happen but wanted you guys to weigh in before I go and start tearing stuff out of the truck. Thanks __________________ 77 Stepside http://67-72chevytrucks.com/vboard/s...d.php?t=422253

09-19-2015, 09:05 PM	#2
bmchevy1979 Registered User Join Date: Dec 2010 Location: Visalia, Ca Posts: 707	Re: 78 K10 Fuel filling secondary tank The return lines to the selector may also be flipped assuming it's a 6port valve __________________ <Brandon> 1974 Chevrolet K5 Blazer 350sbc/SM465/NP205, dana44 front, corp 14bolt rear with 4.10s and a powertrax locker, custom rear bumper 400sbc in the works. 1981 GMC C1500 stepside 250i6, 3spd, 12bolt with 3.08s 2.5/4drop on 15x10 with 275/50r15 81 GMC C3500 cab-chassis dually with utility bed 350sbc, Sm465, 14bolt with 4.10s nv4500 getting ready to go in 1979 Chevrolet K5 R.I.P. http://67-72chevytrucks.com/vboard/s...d.php?t=434096 1976 Chevrolet C10 R.I.P. http://67-72chevytrucks.com/vboard/s...d.php?t=434195

09-24-2015, 08:29 PM	#3
masterlock Registered User Join Date: Jul 2010 Location: San Diego, CA Posts: 281	Re: 78 K10 Fuel filling secondary tank Ok so I figured out the problem and need some more advice. For some reason the return line to the primary tank is disconnected and it is routed into the second tank and it looks as though the return for the second tank is capped at the selector valve. Not sure what the genius behind that was thinking. Anyway I want to know what you guys think as far as options go. Im thinking remove the bed or drop the tanks or just take it to a mechanic and let him fix it. Which would you suggest I do??? __________________ 77 Stepside http://67-72chevytrucks.com/vboard/s...d.php?t=422253

09-25-2015, 11:05 AM	#4
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,630	Re: 78 K10 Fuel filling secondary tank If you have the space, tools and borrowable manpower, pull the bed. It is possible those are the original hoses and if so, they are EOL. Might be why the PO sold it. This way, you can replace all the hoses, check the tank ground wires, fix any cab corner rust issues, fix any bed rust issues and give the underside of the bed a good coat of paint/anti rust coating. For that matter, you could pull the senders out and do a visual inspection of the inside of the tanks.

09-26-2015, 07:38 PM	#7
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,191	Re: 78 K10 Fuel filling secondary tank The tail lights should have a round plug which disconnects near the rear bumper. Also, you might have a trailer plug (lights, brakes) which needs to be removed. I think the vent hose from the differential also is bolted to the frame, so that needs to be disconnected. Of course, the screws holding the filler necks to the bed need to be removed, and if you have a later truck style there may be a metal grounding strap connecting the necks to the frame (a 78 should not have them.) You just need to crawl under the bed and look for anything that connects the bed to the frame. The real problem with removing the bed is the bolts. It is very possible that the bolts are rusted in place and you may snap the bolts off or round out the square mounting holes in the bed floor. So, if the bolts are difficult to remove, it is best just to cut them off and replace the nuts and bolts with new ones. Pre-soaking with PB Blaster or equivalent for a few days is always a good idea. If you don't have an engine hoist, you can jack the bed up with a bottle jack and 4x4s and support it with perpendicular doubled 2x4s on saw horses or stacked concrete blocks when it is high enough to clear the rear tires.

09-27-2015, 10:45 PM	#8
masterlock Registered User Join Date: Jul 2010 Location: San Diego, CA Posts: 281	Re: 78 K10 Fuel filling secondary tank Thanks tucsonjwt, yeah those bolts were a nightmare, I cut some from underneath and ground some down from the top. Then I realized that the reason that the fuel lines were all messed up was because the primary tank was leaking so using the angle grinder became a bit dangerous. So i figure I will just replace both tanks while I have the bed off. I assume that they are 20 gallon. Surprised they are so cheap... Also anyone know what bolt sizes and lengths to get, the one that were in there are destroyed and LMC is smart enough to no list the sizes in the catalog. I would rather pay 2 bucks for a bolt than get them from LMC for 10 bucks __________________ 77 Stepside http://67-72chevytrucks.com/vboard/s...d.php?t=422253

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