drum brakes work until vacumn is connected to booster

[culp71]

so 70 cuda with drum brakes all around, has booster. (bendix style booster, I believe) brakes function perfectly until vacuum is connected from manifold, and or carb. then pedal has no resistance, goes to floor and drums rotate freely...plus a little fluid was forced out of the master cap....thoughts?
bad valve in booster? everything is new.
I removed the line, left fitting on booster open, worked fine. I put a cap on it, also worked fine.
I tried two different vacuum sources, but both cause this "no brake" issue.

[Rich G.]

That's a weird one. Vacuum should have nothing to do with loosing the pedal. I wonder if you have the correct master cyl for power brakes. Do you have the correct rod in the booster?

[Brads70]

power drum brakes? That's a new one on me? 

[71-440]

Bad booster. Probably ruptured internally.

[xx88man]

power drum brakes? That's a new one on me? 

  Never heard of a booster with drum brakes before 

[anlauto]

Yikes...what's the fender tag/broadcast sheet code for power drum brakes ? Certainly an odd duck

[RUNCHARGER]

Huh: Power Drum brakes were quite common.

[6bblgt]

searching for an answer, stumbled across this thread @JH27N0B do you (or anyone) know what the correct casting # is for the master cylinder on a Power Drum Brake '70 R/T w/11" drums?

what's the correct finish for: lid - hold down bracket - bolt?

is this the same BENDIX booster as the "TRANS AM" cars?

to answer a couple above questions - power brakes is power brakes - nothing different on a fender tag = B51

1970 Challenger R/T hardtop JS23 (shipped US):
STANDARD manual drum brakes B11 ~54.7% installation rate (~7,476 cars)
OPTIONAL power drum brakes B11 & B51 ~ 10.9% installation rate (~1,490 cars)
OPTIONAL power disc brakes B41 & B51 ~34.4% installation rate (~4,702 cars)

[anlauto]

Wow...what an odd option to have  Learn something new everyday, thanks Dan

[Brads70]

Thanks ( again) for the education 6bblgt ! 

@culp71  what did you find was the issue?  Bad master or booster? or...? The education continues!