No brake fluid in rear line

Found my brake line that goes to the back of the truck was bad. The master cylinder was replaced before I got the truck. Emissions let me know that the rear brakes were not working. Opened up the rear bleeders and no fluid in them. So, putting the new line in today. What do I need to do to get fluid to the rear?  4x4 F150 replaced the line from the proportion valve to the rear line. Thanks

Do you have a 150 or a 250/350?
The warning light should have come on (unless it's been unplugged)

You need to either push or pull the pin that holds the spool in place in the multi-function valve (brass "proportioning" valve) found below the driver.

There was a bit of discussion about how this really works recently.
I deleted my posts in that thread.....

Bad as in crimped or mashed flat?  Or at least plugged?

Once you replace that then I don't think you'll have a problem getting fluid back there.  But maybe I'm missing something.  

How do I do that do I have to take off the proportion valve completely

It's a 1986 f150 4x4

This was Gary's advice to the gentleman above you:

"The pressure, differential, proportioning and metering valve are three different systems.  (Figs. 4 and 5).  There are three functions of the pressure differential valve: It delays full effectiveness of the front brake, it proportions pressure to the rear system, and it operates a warning system in case of malfunction.  During heavy brake application, the proportioning valve reduces pressure to the rear brakes to avoid lock-up.  The metering valve delays effectiveness of the front disc brake until the rear brake shoes are against the drum."

But there's really not very much to the valve, so you might be able to clean it if the shuttle is stuck to one end.  Here's an illustration of it:

If I remember correctly, Ford's instructions to center the shuttle are to STAND on the brakes with the engine running for boost.  You don't have to be moving, but you need to put a lot of force on the braking system.

However, if there is no flow to the rear, as would happen if the line is crushed, then the valve probably won't move.  So the line has to be good first.

Gary,  Respectfully I'm referring to the multifunction valve found in our generation trucks, NOT the pressure differential valve used on 1967-'72 trucks pictured here.
(From our good friend Keith Dickson at the Fordifction forum)
Hopefully he will not object to my cribbing some of his writeup if credit is given.



To which he says:  This diagram from the Ford Truck Shop Manual isn't 100% accurate, as the factory piece actually used has 5 ports (plus the switch port) as opposed to the 4-port Mustang version showed here. However, the principle is the same.
Unlike a metering valve or a proportioning valve, a pressure differential valve doesn't have any preset pressure settings to delay or to reduce the hydraulic pressure being applied. It's just a spool suspended and balanced inside the valve body between equal pressures of the front and rear brake circuits. If the pressure in either circuit is unequal, the spool is pushed to the low pressure side, closing the switch contacts and illuminating the dash-mounted warning light...simple. It doesn't have any metering function for the front brake circuit and no proportioning function to the rear brake circuit like the all-in-one brake assemblies"

Way farther down the page. https://www.fordification.com/tech/propvalve101.htm  is the correct diagram for our generation trucks.
"
This is the combination valve as used on '73-later trucks equipped with front disc and rear drum brakes for trucks under 6,800# GVW."


Note, on the left, the metering valve bleeder.

I just replaced the bad line. When I stand on the pedal should I have the rear pass bleeder open? Thanks for the info

Yes, to bleed the brakes you need the bleeder open, otherwise the air compresses and just pushes fluid back when you let off the pedal.

IMG_20231112_194830661_HDR.jpg

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Jim - Thanks for that.  

I meant sorry for resetting the proportion Valve. I realized that it would need to be closed.

It seems you have a wet fitting.  
Is there a leak, or did you crack the line nut loose to check for fluid?

Also looks like the spring loaded plunger from the brake warning switch has popped out.
.
Getting the shuttle to move was a challenge 40 years ago when Ford suggested to stand on the pedal.
Crud, corrosion and rock hard O-rings may make it impossible today.
(or, maybe not. I can't speak to the condition of your brake system)

If you have a vacuum bleeder like my Mity-Vac you could fill the cup with fresh fluid and reverse the ports on the pistol to pump fluid from the bleeder towards the master cylinder.
That was the only way I used to be able to get the hydraulic clutch on my GSXR 1100 bled.

I cracked it open to see if I was getting fluid through the line.

Okay then!
That's good to hear  

Note the instructions here.....
You crack the nut or open a FRONT bleeder in order to reset the rear system.
You turn the key to RUN so the brake failure light can tell you when to stop pushing the pedal.
If that spring is what's left of your warning light switch I'm not sure how you know when to stop...

Not sure if this is relevant for this thread…
Big Brother’s parking brake is fully functional, but the truck is also equipped with a pressure parking brake (was legal at that time).
When I use this latter, the brake warning light stays “on” after I release it, until I “reset” the proportioning valve.
I reset it by pushing on the brake pedal very firmly, then I feel a “click” on the pedal and the warning light goes off.
2-3 years ago, the light didn’t want to go off, and after some trials and tests I decided to replace the proportioning valve, everything went back ok.

Thanks, I'm going to try this next. If it doesn't work I'm going to replace the valve.