Sounds like the valve in the prop has shifted and is blocking the rear port. It needs to be centered again by removing the electric sensor. Sometimes a person can use a small jewelers screw driver thru the sensor hole to pry the valve piston back in place. Other times, you need to remove the cap on the end to move it. There is a tool to insert to prevent it from moving when bleeding one end before the other. RPOLS3 has gone thru this recently and bought the tool. The way I avoid this, is by gravity bleeding all 4 corners before pedal/pressure bleeding.

Corvette Central sells the vent tube in the C2 section under air cleaners.

Chevelle brakes...
 

We messed around with this yesterday...not much progress. My buddy took the valve off the car and tried to get the piston centered...i think he damaged it in the process. He has ordered a new valve....

So...when he does the install....should he just do the gravity bleed process you describe..?? Will he need the tool to hold the piston in position.?? If so, who is the best source for that gizmo.

Thanks...wilma

From Jake Dykstra's thread. Unfortunately, he didn't post where he bought the tool.
OK - so some good things happening already this morning. On my way into the office I stopped by my buddies shop for some advice. He tapped the valve lightly with a dead blow hammer after shooting some compressed air into the port and the piston centered on its own. I installed the centering tool to hold it in position.

https://www.yenko.net/forum/attachme...1&d=1646660952

I don't have this tool, and always do the gravity bleed method, in the same order as bleeding..RR, LR, RF, LF.
I do open all 4 to begin with and shut them as fluid appears and then go around in the proper order and let fluid drain for a few seconds each.
Keep checking the master with all 4 open, it can go down quickly at first.

Sounds like you are having the same problem I had with the prop valve. I bought the centering tool from Amazon.

https://www.amazon.com/WISPAUSU-Comp...70711188&psc=1

Thanks Jake, I'm going to get 2 to have on hand also. 1 is $9 and 2 are $11 ?? May as well buy 2...:hmmm:

proportioning valve tool...
 

I just did the same...one for me and one for Gino.

Now when he gets the new valve and tool...should we install with the tool in place and then let the brakes gravity bleed. Then finish with pressure bleeding and when that is good...take out the tool and re-install the idiot switch.

???

wilma

No gravity bleeding necessary with the tool...pump away...:wink:

Pressure switch gets replaced with the centering tool, then pressure bleed, then remove tool and replace pressure switch.