Just bought a '74 F100 with a rebuilt 302 and Holley 650 carb. It's a 2wd automatic with an 8' bed. Had a custom exhaust (stock set up) made to replace the existing glass packs from the previous owner. Just got it back and now it's got a fuel leak from the rear tank. The previous owner stated that he flushed and used the rear tank (I have two tanks both under the truck - middle and back) but didn't do anything with the forward tank. It has new gas in it but I'm afraid to use it since I don't know the condition of the tank.

In the pic, you'll see arrows where gas is present when the truck is running. Basically I'm considering just replacing everything from the tank forward. I may leave the second tank alone for now but I want functioning that I don't have to worry about. I would consider replacing some parts but everything looks old enough to qualify for a replacement. I've seen both 5/16" and 3/8" fuel lines but wasn't sure which were stock for this engine. I've seen some pre-bent lines from ebay and other sites but LMC doesn't seem to carry them for my truck. I have a bender and could get a coil if they aren't to difficult to make up as well.

Just looking for a few answers and some thoughts from anyone who has tackled this in the past. I've done it with other vehicles but welcome any experience from members of the forum.



Rebuilt 302 with 650 holley carb and custom made aluminum shroud

Fuel leaks near the rear tank

 

Welcome to FTE
Nice looking truck you got.

On the tank it could be the rubber hose for the filler neck and maybe the sender on the top have dried out and no longer are sealing?
Being you dont know on the tank side where the leak is and being a PITA to drop I would replace it along with the sender.
I would most likely do the same with the front tank also.
I dont know where you can get the filler neck hose but I would not use radiator hose as it is not made for gas & oil as will get soft over time.
If no one can say where to get the filler hose might try a boat store or shop for it.

On the gas line pick up a coil of copper nickel line and make your own.
As for size I would think for a 302 it would be 5/16 but easy to check.
Get a open end wrench in 5/16 and 3/8 size and slip the open end over the line.
The one that fit is the size you need.
Dave ----

 

Thanks for the quick reply. This is what I found at LMC truck for those lines:

https://www.lmctruck.com/1973-79-for...ler-components

They don't carry the metal filler neck but the hoses seem to be available. Hopefully the metal piece is still in good shape.

Any reason why I can't leave the second tank alone for now? I don't mind doing it but would rather wait until spring. I don't see an issue leaving it from the diagrams (seems like I can just replace everything for the rear tank without touching the froward tank) I found but I've never done it so I'm not entirely sure.

 

I'd want to get up there with a flashlight and mirror and check the top of the tank, I've dropped tanks like this just to do a hose/line and found heavy rust and pinholes all over the top. I've done it enough at this point, if looks questionable and it's something I care about, i just get a new tank, sender, straps, filler, etc., etc., and swap out the whole assembly.

Have you played with the front tank at all,? If it's got good gas in it and it's not leaking, I'd be trying to run off of it. As long as you have a fuel filter in line it'll catch any debris. Maybe grab a spare filter to keep in the truck before you start messing with it. I'd at least want to siphon it out and use it. Letting it sit for the next 4-6 months isn't gonna do it any good. Maybe throw some stabilizer in it if it wasn't getting pumped out?

 

And if it’s a plastic tank like most I’ve seen them it’s not rusting inside. The only junk that would get in there is from the gas stations and probably some water buildup over time.
If the gas is not old, then I’d run some gas additive designed to get rid of water (or use alcohol) and run it as mentioned.
Changing the filter later if you’re not sure. But if it has new gas in it, just run it.

You can easily peek underneath to see if it’s a metal tank or a plastic tank with a metal skid plate.
I don’t know if Ford always used plastic or if there was a certain year were they changed from metal to plastic. But it’s easy to check.

 

I got rid of side tank, I don't drive enough anymore, and it was in the way of fuel and brake line plumbing. If you are thinking of removing and replacing a lot of the fuel system, you may well be better off just pulling the box off. 3/8' seems to be the norm for fuel lines. Check if you're going aftermarket sender. If yours works leave it. Fill hose easy enough to get from several restoration shops. Metal fill tube, check classified ads on this site. Just another tip, get a pcv on the engine.

 

There is no reason to mess with both at the same time other than as someone said it is easier to do tank work with the bed off.
You dont have to remove the bed to do the work.

On the metal filler neck I have not seen the need to replace them as they dont rust out like the tanks do.
I do see the rubber hose used to join the heck to the tank dry and crack then leak.

Before I installed both my tanks I gave a look inside and they looked good so I used them.
Shortly after the truck got on the road I had to pull the top on the carb and found rust in the bowl.
It made it pass 2 filters to get there. Thing is I dont know what tank it came from.
So as someone said check the top of the tanks as I think that is where the rust came from on mine.

I also replced both senders as I did not know if they worked or not, bought truck then took it apart for a 4 year rebuild.
Well about a month after back on the road the rear tank gauge stopped working. Testing pointed to the sender.
I had fun dropping the tank with the bed on and a frame mounted trailer hitch, flare side and no easy way to lift it, bed has to come all a part.
I was able to drop it enough to get sender out and found the float full of gas. I replaced it with one of the used ones and has been fine for the last 3 years.
As someone said it might be best to keep the old sender if they are working.
So just note new dose not mean good now days.
Dave ----

 

If you're going to replace everything from the tank forward, you might as well replace the rear tank while you are there. Its going to start to leak at some point,, best to do it while everything else is apart.

I got my last 73-79 tank from Advance Auto parts. With a discount code it was around $95 shipped. That was a few years back, before the insane inflation of the past couple of years.

 

Bed pulling depends on region, in the salt bed states a few box bolts can reveal a lot, box was one of the last things to go on during assembly

 

I’m a big believer in simply replacing everything fuel related on an older truck. Even if the part is working today, it will likely leave you stranded next week.

I’m fortunate that my 78 F350 used a plastic rear tank. My mid-ship tank was removed by a previous owner so I need to source a new one. I presently run off the tank behind the seat only but intend to pull the bed off next spring to install new mid-ship tank and replace all fuel lines, hoses and sending units. Plus I also want to sandblast and repaint frame etc. from the cab back,

If you have the inclination, it’s not much work to remove the bed and it will make running new fuel line etc so much easier.

 

I checked out the front tank today. Switched it over and ran the truck for a little while. No apparent issues and fortunately it's not leaking. I have a spare fuel filter and will leave it in the truck just in case. I'll try it out for a few days and see how it goes. If it works, I can siphon some gas out of the rear tank and put some sta-bil in it maybe I can leave it until spring.

 

Both tanks are metal - do they make plastic for both the front/rear tanks?

 

Does the bed come off in pieces or can it be removed as a whole?

 

If it is the style side box, it will come of whole. Its 8 bolts I think that fasten it down to the frame. Unplug the rear tail lights, undo the fuel filler hoses and you should be good to go. Oh yah, you might also need 3 strong friends to give you a hand ( offers of cold beer usually helps to secure said friends help... ) Once the bed is off, its also a good time to maybe clean off some rust and throw some Tremclad or Rustoleum on the frame and suspension components.

I'm not sure if they make plastic tanks for the F100 thru F250 series. My truck has a plastic rear tank which is unique to the F350 with the narrower frame rails so it wont fit other F series (except a Highboy F250). If they make a plastic midship tank, I would go that route but will likely have to source a metal tank for my truck.

 

This seems to be connected to the fuel system as well (see pic below). It's located on the floor at the rear of the seat near the driver's door. I know there is a switch on the dash for the main/aux fuel tanks by the climate control

but what does this switch do?