Thanks. It’s complicated. But this is a disc/drum master, as was the one I removed.
The system is a bodge up of parts. Front discs are 70 Chevelle. Rear drums are 78 Malibu. There is a GM brass proportioning valve, mounted on the frame out of sight.
When I got the car, the brakes kinda worked, but with a very low pedal and not very well. No documentation as to what came from where, so I’ve been replacing parts and improving things. Also documenting, so now I know what came from where. Both calipers, both cylinders, all hard and rubber lines, pads, shoes, drums are new. Discs have been turned.
Last year, I took the master and booster off. I can’t identify what came off, but I never could get it to bleed with a hard pedal. I found the pushrod between booster and master was some kind of adjustable thing that had been hacked up to make it fit. In doing so, it flexed all over the place. From pedal (unknown junkyard sourced GM pedal assembly) to booster, there was a tab welded on the pedal arm and some single shear eye bolt looking thing used.
I removed the tab, and tossed the master and booster.
I installed a 66 Impala booster, without the mounting brackets that deal with the angled firewall in the original car. My firewall is vertical. I hooked this with the proper adjustable clevis to the hole in the pedal arm where it belongs. I then put a 70 Chevelle disc/drum master (1 1/8” bore) on and bled it to a hard pedal.
This worked, too well. I have (had) very little pedal travel, like less than 1” from none to all the way hard.
The new master is a 67 Chevelle, disc/drum, 1” bore. I‘m hoping to gain a little bit more pedal travel for better braking feel and reasonable control. I should get slightly longer stroke, and higher line pressure with less pedal effort.
