no brakes after lubing slides and pushing pistons back

[revyurengine]

1997 F-150 , 2 wheel drive , 4.6 triton engine

My father had his RF caliper seize up on him while driving today. Then it seem to free up after rocking the vehicle back and forth, his rim was very hot.
I removed and cleaned his front brakes and sliders, then pushed the dual pistons back into the calipers which seemed to go easily. He then started to pump the brakes to see if they were releasing while I watched and the pistons on both sides only moved out a little , then retracted. They "would not" come back out and squeeze the rotor when he pumped the pedal. (even while engine running)
A local mechanic trouble shot over the phone and said it could be calipers. We changed them with "zero" improvement. We can't even bleed the lines because there's no resistance in the brake pedal at all. Now I'm thinking master cylinder? Any idea how to "bench bleed" them in case we try one?
Dad did say his brake pedal was real low for a few days , then real high and touchy , acting strange.
Any idea how we have no brake pedal pressure now?

Thanks

[jyount]

To bench bleed any master cylinder you need adapter fittings first. Then run some preferrably clear tubing from the outputs back into the resevoir and pump the cylinder slowly until you don't see any more bubbles in it. Don't take the lines off until you are ready to reconnect the lines on the truck. The idea is to minimize the amount of air trapped in the lines between the master cylinder and the fluid that is already downstream of it. Also shut the truck off and put the key in your pocket. Bleed brakes without the vehicle on, ALWAYS. pedal will be stiff, so what. Anti-lock braking systems can interfere with bleeding, for that reason never bleed them with it on.

[jyount]

Also, it is highly suspect that both calipers would seize at the same time. I would say you are on the right track going elsewhere. Hope your calipers weren't to highly priced. Good to replace anyway, but you probably didn't need them.

[jackstrr]

u did put new hoses on didnt u ? also dont push calipers in without bleeder open. you dont want that old crap back into your Mcyl., AND you might damage an internal part with back pressure.

[revyurengine]

Thanks for the replies guys!

I've been researching a bit and hear about a "rabs" valve" They say it's on the frame rail (i haven't checked yet) and this could be causing our symptoms.
What are the fittings coming out of the master cylinder for the rear brakes? One is about 2 inches long and has a spring inside it. The other larger thing is where the brake line goes from the 2 inch fitting to it, before it goes to the back wheels. It has an electrical plug in to it.
Thanks

[revyurengine]

I may have fixed it, so far looks good.

We ended up replacing the master cylinder as it wouldn't push any fluid down the lines. I even blocked off the rear line (rear line with the valves and springs etc) and no better.
I bench bled the new master cylinder then installed and bled the front lines for now , we have good brakes now. Will probably bleed the rear soon.....

Thanks for the information!

Kevin