1976 K10 Dual Tanks - Crossing Fuel Lines

[Shtudwn]

Hello,

I have a 76 K10 that I was told the driveline came loose at some point and tore the tanks up. The owner then replaced them with a custom made square tank on the drivers side. The truck does have the switching valve and the dash selection button.

I have removed the custom tank and sourced two short body tanks. I am working through the wiring and am mostly concerned about the crossing fuel hard lines as there aren't any fuel lines on a crossing frame member. I hope my picture shows up so that you can see this area.

Does anyone have a proper picture of what "I should have" for the crossing hard fuel lines?

Thank you.

[kwmech]

There is supposed to be a cross member under the rear of the cab. Steel lines were used with the shortest amount of rubber needed. the rubber lines shown is asking for a complete burn down of the truck.

https://www.lmctruck.com/1973-87-che...m-advance-line

[Dead Parrot]

Does your valve have three or six hose connections? Depending on emissions levels, some trucks from the mid 70's had different fuel line setups. This will impact the number and size(s) of hard lines crossing between the rails.

From your pic, looks like 1/2 of the back of cab cross member is still there. The hard line(s) used that for support.

[evan]

Originally Posted by kwmech

There is supposed to be a cross member under the rear of the cab. Steel lines were used with the shortest amount of rubber needed. the rubber lines shown is asking for a complete burn down of the truck.

https://www.lmctruck.com/1973-87-che...m-advance-line

This is the way.

[Shtudwn]

"this is the way" ...love that.

I appreciate the link to LMC but if I am not mistaken it is showing all of those lines for a two wheel drive. Are they similar? if I have half of the frame member, as shown in my picture, does the drives side look the same?

and yes, I would never lay the hoses on the mufflers. That would be disastrous

oh .........and I have a 6 inlet selector valve.

Thank you everyone. This is so helpful.

[kwmech]

Shouldn't matter 2 or 4wd. The dual tank set up should be the same

[Dead Parrot]

I am pretty sure the frame cross member was one piece that went all the way across. Possible it was damaged when the drive shaft came loose and the PO cut away the damaged part.

Since your valve is a 6 hole, you will need both cross pieces of hard line.(crossover and return in the LMC pic) A three hole version would have needed only the larger crossover piece.

Another question is do you have a charcoal canister? That would need the vapor line crossover as well.

If that 6 line valve is the solenoid version, last I knew, they are unobtanium. The newer motorized version requires some rewiring. There are threads on the subject.

[Shtudwn]

Thank you dead Parrot....

I did check the frame last night for clues.... and there does appear to be holes exactly matching the side where the brace still exists. I assume that the rivets and cross-member was removed. Might be tough getting a replacement....IDK????

I don't have a charcoal canister.

the valve is a Pollak 6 inlet version.

I am going to stop by the wrecking yard today as I knwo they have a 77 K10 with dual tanks that I have gotten parts from. I will see if I can better understand the layout.

Thank you.

[kwmech]

You can make a x-member with something as simple as a piece of (3/16th) 1-1/2'' angle iron and bolt it in if nothing else is available at the wrecking yards

[hatzie]

I posted a bunch of information on the NL2 dual fuel tank option.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061

Standard convention says that Left and Right are the seated drivers' hands.

You should have three fuel lines crossing over from LH to RH frame rail. Feed, return, and vapor.
Feed and return attach to the valve. Vapor is not connected to the valve. The vapor lines from both tanks tee together on the RH frame rail and run forward to the charcoal evap canister.

You need to be sure that you DO NOT attach the feed and return lines to the valve such that you're returning fuel to the tank opposite the one selected. Blow through the lines on the valve with it powered down and mark the barbs that you can blow through. Those attach to the MAIN tank and the fuel lines to the engine. The two you can't blow through are the connections for the AUX tank.

Your 1976 will have a MAIN AUX switch and a solenoid valve. MAIN is the tank that's selected when the valve is not powered. AUX is selected when the valve is powered up. You can choose which side is the MAIN tank by how you hook up the fuel lines. I usually plumb things so the Left Hand tank is MAIN.

I would use constant tension band clamps or German Fuel Injection clamps on SAE J30R9 or SAE J30R14 fuel hose.
http://67-72chevytrucks.com/vboard/s....php?p=7471241

[Shtudwn]

Thank you very much.

It appears since I have a short box with smaller tanks the crossing piece, for the fuel hard lines, actually sits under the cab (in front of the cab mounts). With that it looks like I will need to make a crossing brace to support the hard lines....and I will have to make those as well.

Thank you to everyone that helped. If anyone has a short box frame image with dual tanks it would be helpful for my fabrication.

[kwmech]

If memory serves, the x-member was riveted to the top flange of the frame and also a single rivet to the body mount as it went across.

[Shtudwn]

Thank you.

I will take a look at that. If I remember correctly that sounds right since there is room there to clear everything.

[Factory Guy]

I stumble across this you tube video a while back and thought it might help you on the routing on the stock hard fuel lines running through the cross member. White arrows show the factory lines (I believe). If you complete your setup this way you definitely can get it away from the mufflers!






for reference heres the youtube video I saw:

https://youtu.be/ZUDnbiCTaUQ

[Shtudwn]

A bit of an update.

The information on the crossing memeber was right in front of my face! Well at least there were some good clues! Lol the crossing piece connects to both cab mount frame mounts. There are 2 holes in each on for this connection. I made a new cross member that is more exaggerated than the original and goes up a bit higher into the cab cavity. I am now connecting the hoses from both tanks and praying I get the hoses connected to the selector valve correctly.

All that being said I am starting to ask myself if I ever had duel tanks? I have holes in both sides of the bed but the switch in the dash is wired with different colors and the connectors look suspect. I am also having trouble with wires. I have a tan wire to the passenger side tank but no other wires???? I also have one red and one blue wire on the drivers side? This checks out back to the firewall but there is no plug at this location. Should there be a firewall junction? There is a light green wire from the switch to the main fuse block.....but nothing going to the selector valve??? I will do my best tp post some pics.

What are your thoughts? If I had the duel tank option would that be listed on my glove box door sheet? It is not.

Thank you.

Dan

[hatzie]

NL2 should show up on your SPID if it came from the factory with dual tanks. I'm assuming the VIN on the SPID matches the one on your LH door pillar and the LH door pillar tag still has the GM rosette rivets so you're sure it's unmolested.

You only need one wire to the tank on each side and one wire to the valve for the 1973-1980 dual tank systems.

Looks like there's some strange hackery going on with the switch plug.

1. The proper five position (six with one blocked) Packard 56 plugs were available a couple years ago. Look up the part number on the GM wiring diagrams. Worst case you can use a six position 12052978 plug.
2. The terminals for the fuel gauge wires have been replaced with 1/4" disconnects with no connector retention tangs instead of the proper 2965867 Packard 56 female terminals.
3. Four wires should run through the firewall in a round molded bulkhead plug.
4. Green and Red with a black stripe are proper for the AUX valve power wiring but that 2 position knockoff Packard plug definitely is not.

If I were in there I'd probably re-terminate the switch wires and insert them in a proper plug. They'll work the way they are but it's pretty cheesy.

[Shtudwn]

Hattie you are awesome! Thank you for the response.

Do you happen to have a source for the pin connectors?

Maybe creating my own harness? I saw on your original post that someone was overnight the sub-harness but when I viewed on their link it said that their account was removed. Are there any other options to purchase a new complete sub harness?

I have read, but will re-read your post on the subject.

I will attach a pic of my SPID. My VIN plate checks and the rivets appear proper.


Thank you again.

[hatzie]

GM used the pin connectors on the fuel senders of various 1960's - late 1980's cars
Look up the fuel sender connection for a 1970 Pontiac GTO or 1973 Nova or 1970 Chevelle.

If your valve is working then just deal with the harness you have in place. Just because the TV guys replace the harness on their no price is too much rebuilds doesn't mean that's the way to do it.
It looks like the wires are all present and accounted for on the switch.

If you don't have a working 1976 solenoid valve you'll need to install an NL2 sub harness for the 1981-91 motorized valve.

[Shtudwn]

Thank you again. I like the way you think!!!

I'm on it...and hoping I have a working selector valve!

Dan

[Shtudwn]

OK, a little update.....

The duel tank switch was added by the previous owner. It was not an ordered item.... which Hatzie pointed out. Not a problem as I went to our local wrecking yard and got everything (switch, switch harness with firewall connector, harness for the duel tanks and selector valve). I also got the selector valve, even though I already had one and they gave me both sending units while they were there. $30 which I thought was great! I have gone through the harness making sure everything is in good shape and will get it installed as soon as I get more GM Harness tape. Having an actual harness makes everything much more clear as to the function of the system.

I am thinking, since my truck is a 76 and the duel tanks I got are from a 85 which has different filler necks (larger from 1 3/16" ID to 1 3/4" ID I think) I might build a crossover tube similar to this one:

http://67-72chevytrucks.com/vboard/s...d.php?t=794870

Has anyone done a crossover tube? Did it work well? Does it fill ok?

Thank you.

[kwmech]

I worked for a 1/4 horse ranch about 35 years ago and we had a crew dually (2wd) that pulled the slant load goose neck,---- loved that truck-----anyways it had the factory dual tanks and an 80gallon bed tank that would fill from both sides. filling that thing was a pain unless I could pull in and take up the center isle and pump in from both sides. That truck loved the fuel.