If you trace the lines off master cylinder they run to back of crossmember for engine as it mounts on backside of cross member and all lines run to it front an back , at least on my 79 its in that location and its about 6 inches long ,, I have seen some on the drivers side frame across from tranny,,just trace your lines and you will find it

 

Grab a flashlight and start doing a visual inspection around your master cylinder, if you're losing that much I have a hard time imagining you won't find it. Or like you mention, get a friend to give you a hand.

You have a lot of learning ahead of you but it is rewarding to understand a system and being able to repair it. Don't be afraid to walk away from something that may be getting the best of you; cooler heads will prevail. YouTube is a fantastic resource you should fully take advantage of before the idiots at the FCC start ruining the internet.

 

I'd say you're right that with that much fluid literally falling out of it, you should see it right away!
Since you found fluid on the floor under the engine compartment, you also know where to concentrate the search. The front reservoir is supposed to be for the rear brakes, but it doesn't sound like the fluid is even getting to the rear brakes in the first place.

The proportioning valve, or combination valve as some call it, is there to do four things.
1. Primarily it's there to reduce the pressure to the rear brakes to avoid premature lockup of the rear tires.
2. It houses the switch that illuminates a lamp on the dash to let you know there is a problem with one of the brake circuits (front or rear).
3. It also has a delay-valve in it (under the rubber boot with the little nipple sticking out of it) which delays the front brakes just a tiny bit so the rears are applied first. This lets the drums take up what might be extra play vs the discs not having such, but also acts to stabilize the vehicle during heavy braking. Kind of like applying the trailer brakes first to keep the tow vehicle straight and not jack-knifing all over the road.
4. Supplementary to all that it acts as a distribution block for all the brake lines to go to their respective locations. I guess that's not so much another function as it is just a necessity.

It should be bolted to the inside of the driver's side frame rail just under the master cylinder near the exhaust tube maybe. The frame is a C-channel there so it's likely "inside" the frame at that point. Might not see it from the top but you can see it lying under the front end. Besides, it'll be the only thing with all the steel brake lines going to it.

It sounds like you haven't had the time yet to follow the brake lines from front to back to look for the leak? If you had you would have seen the valve as well.
Just follow the lines...

Paul

 

Oops! Should have looked for the next page. These guys beat me to it.
You'll find it, and the leak, if you follow the lines.

Paul

 

hi all, thanks for the advice.
i have concluded i need at least new brake lines for the front, but i think i want to get some new ones for the rear as well.
being a noob, i have a few questions.

1, i have looked all over for pre bent lines (i dont trust myself to bend my own), and everywhere i look that says "1978 f250 2wd front brake lines" they seem to be bent differently. can someone who has done brake line replacement on a truck like mine give me a link to a place they used to their success?
2 same as above but for brake hoses, i know they arent "bent" but each place has different looking ones, and i cant find any vids of people doing this repair on a 73-79 ford f series vehicle.
thanks and have a good one!

 

Get you brake hoses from local auto parts store and match to your old , easy to take back if wrong,,the prebent lines I used inline tube , they sell on ebay https://www.ebay.com/itm/1976-79-For...VWT5nY&vxp=mtr this set is for long bed, but they sell for short beds as well,,there are other prebent line sets sold by different vendors, this is just the set I used except I bought stainless but there more exspensive,,and I believe they sell just front set of lines as well ,you just have to do alittle searching,,but the prebend lines are sold also they sell for manual or power brake systems so make sure you buy the right set