master cylinder

[rattlesnake]

My 1970 barracuda was originally 4 wheel manual drum brakes. I installed the full K-member from a 1973 cuda that had disc brakes years ago, I kept the manual brakes and it seemed to be fine. On my recent rebuild I converted to power brakes. I ordered the booster and master cylinder as a unit from NAPA. I installed them and just recently bled the brakes and it seemed to all go well, the pedal is tall and firm. The thing that makes me leery is both reservoirs on the MC I now have are the same size. I saw some photos of some old Chryslers the other day and it reminded me of when I was knee high to a grasshopper, the mopars with disc front and rear drum always had a bigger reservoir in the rear than in the front. So....I am assuming the disc brakes take more fluid to operate. I researched several threads but could not find one to specifically address this topic, so I am requesting input on if this thing is going to work or not. I thought this might be a handy piece of info to have before first test drive.

[72cudamaan]

Yes, typically the rear reservoir is larger and used for the front discs. Without a picture I can't tell how big the
reservoirs are, but if a full stroke of the brake pedal doesn't lower the fluid level substantially then I think you
would be okay. The time it would be a problem is when the pads get worn down quite a bit. You may have to keep
an eye on that.

[rattlesnake]

I will post a pic tomorrow when I get home from work, but basically the MC is split into 2 equal reservoirs. I did purchase and install the correct swivel and rod for the pedal. Is there a difference in the stroke for the MC for drum and drum compared to the drum and disc and could it create problems?

[v21jeff]

There was one larger side because the disc brakes would wear and push out the pistons. If you used one for drum brakes it would not hold enough fluid. I assume the one from NAPA has both sides same size as the disc side.

[Chryco Psycho]

there is no reason the system you have will not work but the issue is as the piston moves out as the pads wear out the fluid is held in the caliper behind the piston so the master can run low on fluid , this is not a problem as long as the fluid levels are checked regularly as the brake pads wear out , you may also have a problem when the pads are replaced & the pistons are retracted into the caliper forcing excessive fluid back into the master .

[rattlesnake]

Cool, thanks yall!! That's good news I would hate to have to change that MC out now. Its always a mess.

[1970 RT Challenger 1970]

What piston bore diameter does your Napa Master Cylinder have? (~1" ?)

I believe the other master cylinders with the small/large reservoir for drum/disc brakes are available in 1-1/16" and 1-1/8", but they say with the 1-1/8" piston bore the brakes are much more sensitive to the brake pedal.