Hi all,

Right before I took three weeks to swap the engine in my '78 a hard rear brake line blew. I left it alone as I knew the truck was going to be laid up for a few weeks. This week I replaced the line and one other, along with a the wheel cylinder at the right rear corner. I tried to bleed the system last night but no fluid will come out at the bleeder screws. I disconnected the line further upstream to see if I had a blockage, and still no fluid. I suspect nothing is getting past the proportioning valve.

According to the Haynes manual the proportioning valve should reset itself with a gentle application of the brakes after bleeding...but I can't bleed it. Can the rod inside the proportioning valve get stuck and close off the rear brake system, preventing any fluid from getting past?

There was no blockage when the line blew as great quantities of brake fluid drained out of the bad line, and the master cylinder would empty the side that serves the rear brakes even if I refilled. Now when I filled it to bleed the system, no fluid left the MC.

How can I reset the proportioning valve to allow fluid past?

Thanks,

Tim
'78 F-150 Ranger

 

You may need to remove the master cylinder and bench bleed it again if air was sucked into it when it ran dry. As for the proportioning valve, mine was stuck when I bought my truck and I had to remove one of the end plugs in the valve and use a pencil to push it back to center. You might be able to recenter it if you open both your front bleeder valves and slowly push the brake pedal down until your brake warning light goes out (if you have one).

 

My first thought is air locked in the master. You can bleed the master in the truck, but you'll need a second person.

Unhook the rear line at the master, have second person hold catch can, rags, and top res.

Only procedure difference is to stroke pedal slowly, and cover the hole before releasing pedal.

Good luck, Mike

 

Try opening the front bleeder screws, have a friend push the pedel to the floor. When the pedel is on the floor tighten the front bleeder screws. Let off the pedel and repeat several times. Then try to bleed the rear brakes as you would normaly. Do not let the master cylinder run out of brake fluid, and when the front bleeder screws are open the back ones must be closed. Good luck
Dave P