deuce fuel line question

[Bill in pa]

Hi Bill in pa here.
!987 M35A2C
What are the function of each fuel line.
There are 3 different sizes.
LARGE.... I pretty sure is the feed from the pump.
MEDIUM....?
SMALL...?

One im guessing is the return?
One im guessing is a vent?

Lastly... Are the fittings standard size go to the hardware store copper fittings?

Thanks for your anticipated replies.

 

[frank8003]

View attachment fuel system best picture.pdf

In the TM's is exact description of every part.
Mostly "hardware store" stuff is no good for your truck. Just fix whatever is the problem with the same as is on whatever you are fixing now.
Photos are helpful, post and ask before making easy fixes into a can of worms.

 

[Bill in pa]

Thanks for the reply.
Do you know what each line on the tank dos?
Are they standard off the shelf fittings?
Bill

 

[silverstate55]

Bill, the large hose is definitely your supply line; the medium line should be the fuel return line, and the smaller line should be a vent line. You can verify supply/return by simply powering on your Start lever in the cab (without engine running), you can hear the in-tank pump whining and soon you should hear the return fuel coming back to the tank.

The fittings are standard at any hydraulic hose shop, or big-rig supply shop. I prefer the hydraulic hose shops, especially if they are affiliated with or a distributor of Parker products...they supply their dealers with some neat hose/fitting ID tools that make instant identification a snap. Your big-box hardware stores probably won't have the necessary types of fittings; most are NPT and compression (make sure you include the hose inserts if present).

 

[rustystud]

Bill, the large hose is definitely your supply line; the medium line should be the fuel return line, and the smaller line should be a vent line. You can verify supply/return by simply powering on your Start lever in the cab (without engine running), you can hear the in-tank pump whining and soon you should hear the return fuel coming back to the tank.

The fittings are standard at any hydraulic hose shop, or big-rig supply shop. I prefer the hydraulic hose shops, especially if they are affiliated with or a distributor of Parker products...they supply their dealers with some neat hose/fitting ID tools that make instant identification a snap. Your big-box hardware stores probably won't have the necessary types of fittings; most are NPT and compression (make sure you include the hose inserts if present).

Just like "silverstate" said. Only use standard industry Hydraulic fittings. They must be DOT approved. DOT fittings are well over twice the thickness of "hardware" store fittings, making them much stronger. I posted the differences a while back. I personally use only "Parker" fittings. Of course I have a store near me which makes it extremely handy.

 

[Bill in pa]

Thanks again for your help.
The large line is the fuel feed from the pump is 1/2 o.d. copper. I cut and flared myself. Its a inverted double flare. Same thing as a brake line.
The medium is the return line is 3/8. I bought a 48" piece of brake line. Again double inverted flare.
The small line for the vent is 3/16. I bought a 48" piece of brake line. Again its a double inverted flair.
I put 15 gallons of fuel in the tank. Turned on the switch and had fuel in the return line.
Started the truck and ran about 5 minutes with no leaks.

 

[silverstate55]

Thanks again for your help.
The large line is the fuel feed from the pump is 1/2 o.d. copper. I cut and flared myself. Its a inverted double flare. Same thing as a brake line.
The medium is the return line is 3/8. I bought a 48" piece of brake line. Again double inverted flare.
The small line for the vent is 3/16. I bought a 48" piece of brake line. Again its a double inverted flair.
I put 15 gallons of fuel in the tank. Turned on the switch and had fuel in the return line.
Started the truck and ran about 5 minutes with no leaks.

Good job!