the pattern for the 4-bolt master starts in 56 [definitely 56 plym at
least] and continues up until 78, in 79 chrysler started using the 2-bolt master
[aspen/volare, cordoba/mirada/magnum]
the difference between the lowboy and regular drum-issue masters and a
disc-brake master is the residual pressure check valve- a drum master has the
valve to retain apply pressure in the system, a disc master does not as a full
pressure retraction is necessary to release the caliper, using a drum master
with discs prematurely wears the pads and creates excess heat- its not enough
pressure to cause a notable drag, but you will see reduced pad
life/efficiency.
the sure-working conversion i [and several others] use is the factory disc
setup found on the aspen/volare, mirada/cord/magnum, and the 80s rwd fifth
ave/diplomats. the spindels have the same balljoint configuration/taper,
the C to C is 1-1/8 shorter, requiring a camber adjustment, the only minor mods
to make are a shortening of the strut rod end to adjust lock-to-lock, and a
notch in the snubber perch to clear the caliper on full lock turning.
as for master cyl, the clearance is a little tight, but i use the 74-77
D100 master cylinder religiously on my 57-9 cars [and a few newer over the years
like my 62 dodge convt] and- if you're using aaj brakes, you probably
already have a GM caliper, so the following tip wont scare you- its obvious the
only safe way to run disc frt/drum rear setup is with a proportioning valve....
the GM A-body prop has the perfect bias for the weight distribution on the 57-9
body. but that info is founded solely on experimentation [i've only done
the entire conversion about 17 times, with 7 awaiting in the next year or so as
i write]
as for the adapter plate, it will bolt on and allow use of the
2-bolt. but instead of buying one, you can just redrill the firewall/plate
to 2-bolt configuration, make a spacer plate to close the area, and use the 4
existing studs to retain the plate... did that twice too, on a
parts-laying-around to fix daily drivers. the spacer is cast and can
crack- pushing the master out of the way=no
stopping
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