R&R brake master cylinder on 1974 Chevy Monte Carlo

For those of you who are wondering, the old master cylinder did NOT leak out the back into the booster – praise the gods of automotive repair. The most tedious part of this job is bleeding the master cylinder. Bleeding alone took me somewhere north 20-minutes, tilting the master cylinder forward then backward, repeat, all the while occasionally tapping it with the leather mallet while working the piston… Removing air from the hydraulic brake system is mission critical. The "hack" I show is something I discovered by chance many years ago while I was working on my 1968 Cadillac. After replacing the master cylinder and bleeding the system as outlined in the shop manual, the brake warning light would occasionally come on during braking which, in this case, was indicative of air in the system. I re-bled the system to the point of flushing both the front discs and rear drums with new fluid. The car stopped well enough but that damn light bugged me. As time went by, I noticed the pads and shoes were wearing unevenly so I changed them out. During the subsequent test drive is when I noticed the pedal felt firmer and the brake warning light didn't come back on. I deduced that a bubble may have been lodged in the proportioning valve and during the process of compressing the caliper pistons and wheel cylinders, forcing the fluid to flow backwards, the bubble became dislodged and made its way to the master cylinder reservoir. I've been using this method ever since and haven't seen any symptoms to discount its validity. Of course, as always, your mileage may vary. Key moments: 0:00 – Opening 0:29 – Introduction and tools needed 2:57 – Removal of old master cylinder 5:50 – Bench bleeding new master cylinder 11:53 – Install new master cylinder 13:04 – Final bleed "hack"