New Member Needs Help with 1970 Fuel Line

[PatrickGMC70]

Hey everyone. I just bought a 1970 C1500 GMC 1/2 ton with a 350. The fuel tank was leaking, and the sending unit was bad, so I opted to replace them. However, I've now found that the previous owner(s) have made some modifications, and I have to change everything back.

The old set-up was a rubber hose connecting two hard lines:






The hacked up line - looks like 5/16" to me:



The new sending unit looks like this (I ordered the sending unit and tank from LMC):





Just under the cab, there is a full filter that doesn't look factory. You can see how it runs down from the cab:



So what I'm wondering is:

1) what size fitting is the adapter that goes in the sending unit? (the nut is 18mm - metric??)

2) are any of these rubber lines supposed to be there, or it is supposed to be a hard line straight from the tank to the pump?

I saw that inline tube sells a 2pc replacement line, but the picture isn't clear enough for me to tell what the original set up was. Also, they sell a 5/16" and a 3/8" line. Is there a reason to change this over to 3/8"?

Does anyone know where I can get a grommet to fill the hole in the floor where the fuel line goes through? I haven't seen it in any catalogs.

3) I assume that fuel filter is not stock - can anyone confirm this?


If anyone has pictures of what this is supposed to look like, I'd really appreciate them. I don't want to "make it work" - I want to make it right.



Sorry for all of the questions in one post, but I REALLY want to get this thing running asap. Thanks in advance for all of your help!

[Hubscrub]

my 71 has the steel line from the sending unit down out the cab to a rubber line, to a steel line that runs along the frame to near the fuel pump then the rubber line to the pump. the 5/16 where on inline 6 trucks and the 3/8 where on v-8 trucks i believe, i am running a 5/16 on a mild 350 and it does fine and no that filter is not stock

[PatrickGMC70]

Thanks for the fast reply!

When it was running it seemed to run just fine with the 5/16 line, but I was driving it pretty easy.

By my thinking, there must have been some V8 trucks with the 5/16 because why else sell a kit with the 5/16?

If there should be just a rubber line where that filter is now, then maybe I'll just repair the section that runs from the filter to the tank, and leave the section that runs to the pump alone, since it looks like its in good shape.

[PanelDeland]

I would keep the filter(actually replace it with a new one) just for that much better filtration to the carb.The fitting would be easy to match.Just remove the sending unit and take it with you to the APS.Don't forget to prime the carb when you start it.No sense in working the starter any harder than required.

[PatrickGMC70]

I just got the tank installed. "Direct fit" my ass! Well, it's in, so I'm happy.

I'm off to the store to see what I can get to replace this line and fittings. (The line on the frame rail looked good. All the same, I'll pick up some brand new rubber and clamps for the section between the frame line and the line to the tank. Cheap insurance.

As for keeping the filter, I've seen some posts while I was searching on here that a filter between the pump and tank was not a good idea because it made the pump work harder. (Of course, I'm leaving the filter that goes into the card.)

When you say prime the carb, I assume you mean to make sure that the fuel bowl is full. Sorry for the newb question, but I'm used to FI cars - this is my first carb engine.

Thanks again for all the help!

[Shyguy]

The fuel filter under the cab can cause vapor lock problems.

That being said a lot of people run one there when they buy a truck with an old dirty tank for a while until the tank is cleaned out.

The only filter stock on most of these trucks was a small fuel filter in the carb inlet. A lot of us remove the small filter at the carb inlet and put a metal filter between the fuel pump and the carb.

Danny

[El Jay]

Plastic & glass filters are nice to look at; but if they get banged & broken they become immediate fire hazards. If you're going to keep that filter, I would replace it with a steel one. Just my .02.

[PatrickGMC70]

Wow. A lot of good advice here. I took the filter out. If it was good enough for GM, it's good enough for me. The old tank had a ton of crud and rust in it, but with a new tank, I think I should be good to go. She started up with no problems at all.

BTW, I had to get 3/8" line because that was the size of the fitting for the new sending unit. Now, there's only about 3" of rubber hose connecting the tank line with the line on the frame.

Tomorrow's project is to get the seat back in, check the filter at the carb inlet, and go for a cruise. Thanks again everyone.