It all started when I had the fl brake hose disconnected while adding braided brake hoses and the master cylinder went dry. I bled the entire system and no fluid to the rear. New parts so far; master cylinder, brake booster, front calipers, pads and rotors, rear wheel cylinders and all hoses are now braided. I can bleed the front brakes no issues but the rear sometimes flows some fluid when bleeding then nothing else comes out. The proportioning valve pin does move in and out when pressing the pedal. Ive gone through multiple bottles of fluid so far and no matter what I do I cant get pressure to the rear brakes. Ive bled everything multiple times from the master cylinder to the rwal and proportioning valve and those bleed fine. Could it possibly be my proportioning or rwal valve? The abs and brake light are on steady. A little note ive had no issues with the brake system on this truck until now.

 

You most likely have to bleed out the master cylinder since it went dry. The pin in the proportioning valve that moves back and fourth inside needs to be centered so fluid flows on both sides of it to hold it there. When it hits one side or the other of the valve it turns on the light.

 

The master cylinder is new and has been bench bled several times and bled on the truck. Ive even replaced the new master cylinder and repeated the process and still no rear brakes.

 

Much like trouble shooting electrical start at the source and work your way out looking for pressure at each connection.

 

I have pressure at the master cylinder, proportioning valve, rwal and the intermittently to the rear wheel cylinders but thinking the proportioning valve is only letting enough fluid through for the beginning of the bleeding then loses pressure.

 

Grab a friend, have your friend pump up the brakes, and hold the pressure. Open one of the FRONT bleeder valves.

The proportioning valve is simply doing it's job. If one circuit, or the other, fails, it attempts to block that circuit. Currently, it is blocking the rear, so, releasing pressure on the front, will make it want to go the other way. You know you have it right, when the brake lite stays off when you step on the brake pedal.

 

Does it matter if I have full hydraulic pressure and no air in the front brakes and no issues there? We have tried bleeding the front again and have no air up front plenty of fluid coming out when bleeding the fronts?

 

What you can try is too open your front bleeder screws let the fluid pump out!!!, pump up the brakes refill pump up and refill leaving front calipers fluid to flow out, and then bleed the rears! I had this same issue with my 96 second gen and that was what I had to do! (Bleed the rears before closing your front bleeders screws) the when your fluid flows good reblead the fronts! Good luck I hope it works out for you