I pulled the booster out last night thinking I might be able to use my existing master cylinder for a manual setup, but didn't work out. The pedal linkage rod is not easily removable from the booster so I'll have to order a manual pedal linkage rod before I can try that. I measured the back of the master cylinder with calipers while I had it apart, and got around 1.065" which seems odd. I don't think GM had a 1-1/16" bore option. I'm still thinking it's a 1" bore and there's just a little larger opening at the area I can measure.
Keep in mind, I've been researching and planning for this brake upgrade for over 10 years. I've done a lot of reading and learning while trying to plan something out that I could afford. I'm not some completely ignorant fool who just wanted random people on the internet to do all the research for me and tell me what to do. I've talked to most of the "brake suppliers" over that time and have not been overly impressed by their supposed professional advice.
The pedal ratio is the same as all GM A-body's of that era, about 3.5:1 for the power brake hole and about 6:1 for the manual brake hole. It's currently in the power brake hole because I have power brakes and because the booster is at an angle that only allows connection to the power brake position. I will use the 6:1 manual position if/when I go to a manual setup.
I'm using the stock drum/drum distribution block (for now). I thought I'd try it that way before adding an adjustable proportioning valve to the rear brakes based on feedback I read on the internet indicating that it typically ended up adjusted to full open anyway. So far I have not encountered rear lock up with it the way it is.
I have good high quality new pads that are either GG rated or GH rated - I can't remember now and I forgot to take a picture for reference.
I do plan to eventually replace the master cylinder with a new one, because then my entire brake system will be new. I wanted to get a point of reference from what I have now to determine what to go with. Right now I'm leaning toward trying to find a suitable 1" or 15/16" bore manual master cylinder - preferably in aluminum and much less than Wilwood's overpriced $300 units.
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