The Slantsix Dan recommends the '71 and later MC36338. Is that OK for non-power assist disc brakes going into my 67 A-body? There is some difference between disc and drum brake master cylinders, the drum brake ones used to need a residual pressure valve to keep the wheel cylinders in readiness? Also, I'll need a proportioning valve for the rear drums?

That depends on if the MC is for a drum/drum or a disc/drum setup. I highly doubt it's for a disc/disc setup, so I'll assume Dan recommended one that's for a disc/drum setup. In which case, you will not need either a residual valve or a proportioning valve, but you will need the (if I remember the year correctly) '72-up distribution block and you may want to use smaller wheel cylinders for your rear drums to prevent premature rear wheel lockup. Do a search and you'll find the right P/N for the wheel cylinders. I'd just tell you but I have issues with the search function when I log in here from work.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Disc/Drum setups DO benefit from the use of a proportioning valve and residual pressure as well. The proportioning valve is needed because of the servo, non-linear operation of drum brakes.

Disc brakes are linear in operation. When pedal pressure is doubled the braking force is likewise doubled. When pedal pressure is doubled on servo type drum brakes the braking force is quadrupled. Without the prop valve the rear brakes will almost certainly lock up prematurely and seriously reduce brake performance.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Dakight is right — you definitely do need a proportioning valve if you have rear drum brakes! Are your rear brakes 9" or 10" drums? Residual-pressure valves were withdrawn from production after 1972, because wheel cylinder seals were redesigned to prevent air ingress. As long as you run new rear wheel cylinders (use 13/16" bore ones, not stock 15/16", if you have 10" or 11" rear drums), the RP valve is optional — you can run one for "belt and suspenders" protection against air ingress, if you want.

Which master cylinder to pick depends on whether you want an easier-to-push, longer-throw pedal or a harder-to-push, shorter-throw pedal. I find a 1" bore is just about right with organic (not metallic) brake pads. The 1" masters were used thru '70 and are getting hard to find. '71-up choices are 15/16" or 1-1/32", just under or just over 1".

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks. I'm planning to retain my 9" rear drums. Does that limit my options, or can I run a later MC with new wheel cylinders? Is there a procedure for setting the proportioning valve, or is it by trial and error?

Well, that'll help reduce rear-lockup problems! To be safe, use a residual pressure valve. If you don't wind up with a master cylinder so equipped, add one inline.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.