New master cylinder brake bleeding help

[rockingm82]

Just installed a new master cylinder.

Bench bled the master cylinder to a no bubble state.

Ran new brake lines from the master cylinder to the proportioning valve.

Bleeding the lines and it is going really slow. Just get a trickle of old brake fluid when opening the rear wheel's valve. The brake fluid is clear not then red that has been installed.

Do we just keep at it or is something wrong?

-Novice mechanic.

Thanks

 

[rockingm82]

Reading some previous posts, I'm beginning to wonder if I have a bad master cylinder.

I bled the lines over and over today thinking maybe something would change. Brake pedal still goes easily to the floor. I then went and purchased a vacuum bleed kit. I got the same results after using the vacuum bleeder.

Beyond frustrating.

Some background.
I'm running a front disc rear drum master cylinder to a proportioning valve I purchased from Bronco Graveyard. I am using the Chevy front disc conversion.

 

[Apogee]

A quick way to verify whether the master cylinder is functioning like it should would be to plug both outlet ports and then stroke it, either by hand in a vice during bench bleeding, or in the vehicle. If it hydraulically locks almost immediately and doesn't sink over time with steady pressure applied, then it should be okay. I use the plugged port bleed method pretty much exclusively for this and other reasons, however it still serves as a good verification even if you chose to use the recirculation bleed method. Some people here will say they never bench bleed their master cylinders...while I'd be lying if I said I wasn't jealous of their luck, I would ignore that advice.

From that point, I would attach one circuit at a time, waiting to connect the other circuit until you get a good pedal with only half the system in play. In my experience, fewer variables are easier to juggle at one time than more variables, so plan accordingly and be methodical.

Once you get a good pedal with just the front or rear brakes, then attach the other circuit and work your way through that end of the vehicle. Using this method, you should at least know where the issue is, if there is one, allowing you to focus your energies there rather than everywhere at once.

 

[ntsqd]

The novice mechanic comment makes me ask did you start with the brake that has the longest length of tubing to the master cylinder? Usually that is the right rear, but always follow the plumbing and don't take that for granted.