Need picture of 1974 1975 brake booster or seller of one

[Mr C]

The rear disc brake axle is not simple! I think that even axle shafts are different when compared to a rear axle with drums. I don`t have to say that you may be able to find reproduced gear sets and Sure-Grip units and that`s it.

The 74/75 Imperial 9.25 differences are confined to the rear disc items...everything else is the same. They are pretty simple...it's a live axle! Unless simple equates to "easy to find parts" in your post above-in which case the 74/75 rear discs are not easy. If you wanted to swap back to drums, it's literally a bolt on proposition (swap caliper brackets for backing plates etc.). These systems made for the best braking I've ever experienced in a C body.

 

[MN72Fury]

You're almost there, just get the master cylinder you need, and it should work. I don't know if you'd need a specific booster, maybe a disc/drum off a C body, not imperial specific, to make it all play nice together. Still have to see this car, we had two '72's at Farmington this past June, a new record! (Both owners are members of the F_BO family too.)

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My goal is to be there next year with my car. I was there but missed both 72's

 

[MN72Fury]

Thank you Mr C.

@MN72Fury ... the 50/50 master is so the rear brake circuit won't run out of fluid, it isn't so special otherwise. It is possible to use a rear drum master from a Formal (and many other cars) but you want to remove the residual pressure valve from the port (if one's there). This stuff is shown in the FSM, but for repair purposes... don't expect a tutorial for modifications.
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Metering valve could cause the opposite effect of what you described
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I think someone else mentioned checking the hoses... don't bother if they're old, just get new ones. A brake hose can fail internally and a little flap of rubber can act as a valve to block or hold pressure... a pretty common problem with an old or abused hose.

Thank you!