Bad Master Cylinder?

[AZ Highlander]

So, I have replaced the hoses, hard lines on the axle, proportioning valve, cylinders, calipers, and all pads, springs, etc.
Blew out the rear line with compressed air from proportioning valve to block on the rear diff. Made a mess.
Got flow to front just fine still.
No flow to rear. No flow to rear hose. No flow out of master cylinder for rear line.

The MC is still mounted on the vehicle, but I tried bleeding the MC with my son pumping and holding the pedal.
Bled the front brake line out of the MC just fine (closest to cab) and some air was escaping.
I don't believe the front line's reservoir tank ever went dry since I have owned the vehicle.
The rear line seems to sputter a little when the nut is loose and the pedal is pushed, but no fluid comes out. Maybe a drop or two at most. Always had my son continue to push on the pedal while I cracked loose the nut on the line at the master cylinder. He said the pedal dropped when I cracked the front line, but not the rear (probably because no fluid came out).
Reservoir lid is on. Tried with engine running, but same result.
Any ideas? Any reason to take the master cylinder off the vehicle and bench bleed?
Must be full of air in that section farthest from the cab. How do I get fluid in there?
Is it just a bad master cylinder? Needs to be replaced?

 

[74Blaze]

Try Stomping on the brake pedal like during a Panick stop. Then try to bleed it again. I've had that work before.

 

[AZ Highlander]

Try Stomping on the brake pedal like during a Panick stop. Then try to bleed it again. I've had that work before.

with engine on or off?

 

[AZ Highlander]

with engine on or off?

tried both. no dice.

 

[85K304SPD]

You've already replaced about everything else, so why not replace the master cylinder too? It is pretty common for them to stop working correctly. You could rebuild it, but the parts stores have them ready to install for a reasonable price.

 

[AZ Highlander]

It turns out I have a friend in the next town over with a master cylinder he pulled and kept around after he installed hydroboost.
Things are looking up!

 

[75gmck25]

The proportioning valve balances front and rear brakes. If front or rear brakes has a big leak, the prop valve will flip the other direction from the leak (and turn the brake warning light on) and it might stick there. You should make sure the valve is centered so it’s sending fluid to the entire system.

 

[Bextreme04]

It turns out I have a friend in the next town over with a master cylinder he pulled and kept around after he installed hydroboost.
Things are looking up!

A brand new ACDelco one is only $38 with free overnight delivery if you have prime. If your buddies old one ends up being no good, I'd just order a new one in.

https://www.amazon.com/dp/B000QGQRD2/

 

[AZ Highlander]

The proportioning valve balances front and rear brakes. If front or rear brakes has a big leak, the prop valve will flip the other direction from the leak (and turn the brake warning light on) and it might stick there. You should make sure the valve is centered so it’s sending fluid to the entire system.

I plan to. Not getting fluid out both sides of the master cylinder at the moment however.

 

[AZ Highlander]

A brand new ACDelco one is only $38 with free overnight delivery if you have prime. If your buddies old one ends up being no good, I'd just order a new one in.

https://www.amazon.com/dp/B000QGQRD2/

Thanks Eric. I have that one in my cart as I type this. I plan to order it immediately after a failed bleed attempt on the one I am picking up from my friend.

 

[CountKrunk]

Did you end up ordering a new one?

 

[AZ Highlander]

Did you end up ordering a new one?

Got one from a friend but haven’t had a chance to install it yet

 

[AZ Highlander]

Same result with my friends master cylinder. It seemed like the rear was bleeding ok for the first crack, then got worse the next few times, then this on the fourth or fifth

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[Bextreme04]

Same result with my friends master cylinder. It seemed like the rear was bleeding ok for the first crack, then got worse the next few times, then this on the fourth or fifth

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What is that supposed to be showing? Make sure you have the reservoir full, then make sure you are getting fluid flowing out of the rear bleeder before you start pumping the air out. You might have so much air in it that you are sucking it back into the master by pumping it with the lines empty. Pumping it when the rear line is empty can also cause the prop valve to snap over and block it off.

 

[AZ Highlander]

What is that supposed to be showing? Make sure you have the reservoir full, then make sure you are getting fluid flowing out of the rear bleeder before you start pumping the air out. You might have so much air in it that you are sucking it back into the master by pumping it with the lines empty. Pumping it when the rear line is empty can also cause the prop valve to snap over and block it off.

It is showing Bleeding the master cylinder is not working. I could be doing it wrong, but can’t get all the air out of the master. Isn’t that the first thing to do? From all I’ve read and watched, you can bleed the master on or off the vehicle and it doesn’t need lines attached.