Hello,
I have all of the disc brake parts for my conversion on my 71 dart, minus the master cylinder and prop valve. I was doing some reading, and I came across this:

http://www.jimsautoparts.com/mopar_perf ... brakes.htm

Since the pressure is regulated in the master cylinder, this would mean a prop valve is not needed...correct?

Incorrect. You do need a proportioning valve in your disc/drum system. All the factory-installed disc/drum setups have a prop valve. The factory valve fails to prevent premature rear lockup, but the rears would lock a whole heck of a lot sooner than they do if the prop valve weren't there.

Factory-type prop valve + change rear wheel cylinders from 15/16" to 13/16" bore (Raybestos WC37696) = excellent system balance.

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

Ok thanks. The porportioning valve on that site should work, correct? Do you have a part number for one that an autoparts store sells? This one is fairly expensive.

http://www.jimsautoparts.com/mopar_perf ... brakes.htm

Also Dan, do you have any Master Cylinders that you reccomend? I am doing a power brake conversion along with putting on disc, but I don't have a master cylinder. I don't want to get some rebuilt piece of crap. Would the one on this site be good? Or do you have a better suggestion?

Thanks!

I like to use a '67-'70 A-body disc brake master cylinder (1" bore) without a booster, but these are getting really hard to find, and you seem to want power brakes. What kind of booster will you be using?

The prop valve on that site is an adjustable one. The factory valves are non-adjustable. Neither type is a parts store item.

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

Dulcich does a group buy on some aluminum master cylinders. If enough interest on here and other places? It might be time to do another.

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Is the size of the drum a factor when choosing a smaller wheel cylinder?

9, 10, and 11" drums

10", 11", and 12" drum brakes all use the same type of wheel cylinders, and they are available with bores of 3/4", 13/16", 7/8", and 15/16" (and possibly 1", haven't checked). Most applications including A-bodies with 10" rear drums got 15/16"-bore rear wheel cylinders. Reducing the bore of the rear wheel cylinders greatly reduces (or eliminates) the tendency for premature rear lockup, permitting much greater braking action overall without loss of control. I don't argue that every vehicle should immediately get a set of 13/16" wheel cylinders, but there are some vehicle setups (such as A-bodies with front discs) that are so predictably prone to early rear lockup that I consider the swap a no-brainer in cases like that. In other cases, it's more along the lines of "H'mm...the rears lock up when I stand on the brakes, think I'll try a smaller set of rear wheel cylinders". That's how my thinking went on my '89 D100 pickup, on which I just replaced the 15/16" rear cylinders with 13/16" items. Result is perfect: no more rear lockup, and much better overall pedal feel and braking action. I try to balance the system front/rear this way before I restrict pressure to the rear with an adjustable proportioning valve.

9" brakes use their own type of wheel cylinder, so bore size swapping can't happen.

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