When I got my 71 Cutlass Supreme Convertible, the brakes were awful. I replaced the master cylinder, prop valve and booster with a kit I got from Inline Tube and replaced the lines with SS ones from the same place. New calipers, fresh wheel cylinders, etc., etc. The brakes were amazing after all that!

For a while, all was working. Recently, though, I have noticed that I cannot stop the car like I used to be able to. Right now, if I stomp hard on the brakes, the car will eventually come to a stop --- but if I had done that last year, it would have locked all 4 wheels. In a panic stop right now, I'd be in trouble... I get a firm pedal, just not much braking power.

I just yesterday replaced the master cylinder (again) with a new one from Summit, but that behaves exactly the same as the old one. I am considering just replacing the entire booster, m/c and prop valve (again) to get reasonable stopping again. I am thinking it is probably the booster, just because so many threads seem to reference it (here's one). Before I pull the trigger on that, does anyone have any suggestions as to what I should try? Should I replace just the booster? Is there a good brand I should try (want to keep it stock looking)?

Here's what I have tried so far:

• Replaced the master cylinder (yesterday).
• Bled and bled and bled the system many, many times. Using a pressure bleeder, using a helper, using a vacuum pump.
• Dug into the drums looking for leakage or problems (nope).
• Pulled apart the calipers looking for anything out of the ordinary. I saw that the shims on both outboard pads have broken and slipped (see below), but I doubt if that is the cause.

Otherwise, things look pretty good. I'll swap the pads, but anything else I should try?