Can a power disc master cylinder work with power drums?

Slabside500

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Long story short, the master brake cylinder in my 1968 Dodge Monaco is starting to fail, it's equipped with power drum brakes on all four corners. Via an old buddy of my father's I found a year correct NOS master cylinder, but it's for a power front disc/ rear drum setup. It looks like it'll bolt into place no problem, but I'm a bit of a novice when it comes to braking systems, not sure if it'll work with my application. When time and money is available I'm planning to convert to front discs, but that may be a long time off from now. Any help is appreciated!
 

Boydsdodge

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I want to say you should be good to go. But I thinking you should just go a reman unit for your car until you do the disc swap. They are pretty inexpensive.
 

Lee Robinson

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I want to say you should be good to go. But I thinking you should just go a reman unit for your car until you do the disc swap. They are pretty inexpensive.
Put discs on the front as soon as you can. It will stop straight and you won't have worry which way it's going to go if you hit the brakes hard.
 

70bigblockdodge

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It will work fine. I have a disc brake master on my Charger and have yet to change to disc, maybe this winter. Pretty far down on the list since the drums work well.
 

volksworld

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in the good old days of parts books you could look this stuff up...if the bore of both masters is the same you're good to go...usually the only difference between disc and drum masters is the increased resevoir capacity for the discs as the calipers have to fill with fluid as the pads wear...but another consideration is the condition of an NOS master...seals could be dried out or bore rusted
 

70bigblockdodge

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If the bore size is different it will only change pedal pressure, (not really noticable on power brake) and travel (could be noticable when you put the disc brakes on). On power brake cars I usually try to increase the bore size of master if possible to reduce the pedal travel because it hangs so low in the first place.
I think the range in master cylinder bores for this era is around 15/16" (A body manual drum) to C body/Imperial power brake or Hemi cars @ 1 1/8" bore.
 

Mike66Chryslers

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Drum MCs usually have residual pressure valves in both circuits. Disc MCs do not have a residual pressure valve on the disc circuit. Some people say the residual pressure valve is not needed, that there is no danger of air getting into the system past the seals on the wheel cylinders because the MC is at the high point of the brake system. YMMV
 

cbarge

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From my experience....no.
Frankie had a disc brake master on it and no brakes.
Put the correct 4whl drum master on it...got brakes.
 
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