Quick queries about '73 rm300 brake fluid levels.

[Dunnohow2]

Hi all. To date I have done the following and have a few (!) queries for the brake gods and goddesses:

Replaced master cylinder and booster;
Bench bled the master cylinder
Fitted the above;
Cleaned and refitted the cab air filter and pipe for the booster;
Replaced the vacuum pipe to the booster;
Bled the brakes except the driver rear which is tight enough to snap if I reef on it, despite oodles of penetrating fluid;

Left the vehicle standing for a month or more and both front and rear reservoir levels were down about half way with the rubber gasket pockets sucked down;

Topped both up and looked for leaks but found none;
Left vehicle for 2-3 weeks and the front reservoir level was down about a quarter.

My few queries...
Would any air trapped in the lines make its way back to the master cylinder while standing?
Any recommended i.e. guaranteed ways to loosen the stubborn fluid bleeder?
I have been looking for fluid leak trails at each wheel but could the fluid be puddling in a drum or somewhere and remain unseen?
Does the front reservoir only operate the front discs and the rear, the rear drum brakes?
Should I do anything to the metering valve? The brake warning light does not come on but could it be broken??
Lastly, what level of vacuum is needed for the booster to operate?

As ever, your help and suggestions will be greatly appreciated.  It seems that the more brake manuals I have, the more difficulties result!  I'm off to make a one-way valve bleeder by tightly tying and taping a balloon to my bleeding tube and use another can of penetrating spray...ho hum.

Happiness to everyone for all times,
jenni.

[brians69d24]

On my 69 m300, the front master cylinder chamber goes to the rear circuit. It does sound like you have leak. Possibly one of the wheel cylinders or maybe the brake booster. If you have a vacuum booster, it might be leaking into the chamber.

How does the pedal feel? spongy? If the brakes were bled, there should be no air making it's way back to the master cylinder. I would kinda doubt that would happen anyways.

I would agree that you need to get that bleeder open. I don't think you can use heat on it because of the rubber.  If you snap it, I do believe there are kits available to insert a new fitting in there...although I personally haven't  used one.  What kind of shape are the lines and hoses in? Have they ever been replaced? As you know, the MH is 40 years old.

Don't know about the vacuum question, Dave is the resident Dodge brake guru. 
brian

[ClydesdaleKevin]

Don't forget you also have bleeders on both brake boosters, and you have to bleed those first before bleeding the rest of the system.  And to properly bleed the system, you'll have to get that rear bleeder screw out, even if it means replacing the wheel cylinder its stuck in. 

Possible places for a leak that you won't find all to easily would be internally in the boosters, or from one of the wheel cylinders leaking into the drum but not enough to spill out of the drum and onto the ground.

We bought a hand pump type vacuum bleeder when we did our old 72, and it made all the difference in the world.

Kev