OK gents, time to report in after a week away. I am determined ultimately to write up the solution to benefit someone else. Some threads I have seen elsewhere just end in the middle, and the reader has no idea what happened. No lesson learned.
As to where I am now, well it is a good thing I learned to have a grim sense of humor in the Army. Stuff went wrong there all the time too, LOL.
Booster Push Rod
Going into this week, I was absolutely convinced the root cause of my problem, a pedal that grabs close to the floor, was that the booster push rod was not adjusted properly, and that there was too great a gap between it and the piston in the MC. I bought a guage to measure the gap and adjust it.
So here is the result. Or lack of a result...
On the booster pushrod gap, I unbolted the MC, moved it as far aside as I could, and used the guage to measure the MC depth (to the piston inside). Once I pushed the guage rod into the MC, clamped the rod and reversed the guage, I found that the guage legs (deep side toward the booster as required) would not touch the booster. To my astonishment the push rod was adjusted a bit too far forward (toward the MC), not backward (toward the firewall). This showed that I had to adjust the push rod in the opposite direction than I expected and pretty much killed my hypothesis about the booster push rod causing the low pedal engagement. I put a .010 gap between guage rod and booster push rod and put the MC back in place. While the MC was off, I did determine that it was not leaking into the booster. It was dry.
Rear Brakes
The rear brakes have been driving me a bit nuts, but one reason I have been trying hard to adjust them is my understanding that if the rear brake shoes are too loose, it is another reason that the power brake pedal can grab (or engage) too close to the floor, with a lot of pedal travel before the brakes hook up. I watched a whole video on this just a couple of days ago, where a repair shop was adjusting the rear brakes on a 94 Chevy truck. The situation sounded a lot like what has been happening with my Challenger. They did not do much to those brakes (e.g., they did not replace the old drums). They just adjusted the shoes out and then felt for some grab when putting the drums on. They then rotated the drums and listened for that hissing noise that indicates light drag. They immediately felt grab, just an inch at most into pedal travel with the engine on. This was encouraging.
I also saw a video demonstrating how to use a drum brake guage, which I do not have. But I got the drift.
However, I simply cannot get that sound indicating light drag. I do not have a guage so I just put the drums on and off and rotated the adjuster outwards until I needed to push just a tad (and I mean a tad) to get the drums on over the shoes. I then rotated the drums, but at that point it was actually pretty difficult to rotate them. I then tightened up the e-brake cable until it was really difficult to rotate the drums. I figured that at least this would prove one way or another whether I had pedal. Just a note, even with the difficulty rotating the drums with the e-brake off, I can depress my e-brake foot pedal almost to the floor. I am guessing it should only go down a few notches. The cables are brand new. This is a confusing scenario.
Test
Today I put the car up on dollies and rotated it so I could try backing it up and driving it forward in the garage. Naturally I tripped over the jack handle, which makes twice this week...
As soon as I put the key in the ignition, the horn sounded and continued to do so until I disconnected the horns from the harness... The chrome key slot with indicator has become very loose and rotates freely, and I now have no left or right turn signals. I recently put the column back in the car. The key slot part was loose before I took the column out, but everything was working then. I guess I have some diagnosing to do and maybe a new ignition switch is necessary. A future thread.
So, with that mess out of the way, I proceeded to test the booster: pump pedal several times with engine off to clear vacuum and get a firm pedal; hold pedal down, start engine, pedal should go down. This test worked perfectly on my 2013 Challenger as a control. On my 73, I could not get a firm pedal when pumping with the engine off. I have to redo the test and make sure I didn't do something out of sequence. I started the car with my foot on the brake and the pedal did not go down. I have to redo this test and then try a vacuum leak test and recovery test before deciding that this brand new booster doesn't work.
I tried going forward and backward a few times and the pedal on the car feels stiffer than before I adjusted the booster push rod. But the pedal still goes way down toward the floor before I start to feel any engagement. On my modern Challenger, even with light pressure, I feel the brakes engage almost immediately. I am not sure why the power brakes in the 73 would feel much different. Something is clearly out of whack; potentially I need to bleed the brakes again.
Anyway that is the news from Lake Woebegone, where the brakes are way below average.
Cheers...
