got a ??? if a person swaps from 68 front drum to 75 front disc, does he have to remove the distubution block that was used on the factory drum set up??

only if you replace it with another

You still need a PP valve.They have one that is adjustable and you can leave the drum block in place.Just plumb it to the rear brakes.Rocky

A body I'm assuming. Ideally you would want to replace it w an A body disc/drum prop valve (that works and is functioning) or it has been posted that an M body prop valve has better proportioning. It has been recommended to keep the drum/drum splitter & add an adjustable aftermarket prop valve in the rear drum line but a guy here that this would allow immediate (& too much psi) to the front discs wearing them excessively as they shouldn't have psi until the drums are expanded a bit & ready to make contact which does make sense. But with that being said I have (on a 65 dart), 73 A body front discs & 10" drums on the rear (7&1/4) w the orig drum/drum splitter & no issues (& no prop valve) but I just put around town & guy here on Moparts sold me a set of semi met front pads for $15 & if they wear out too fast it's not a big deal.

That or like I said leave it and install an adjustable one on the rear line.Ive had a few guys say they dont run a PP valve.I wouldnt try that though.Rocky

I have a Volarie PP in my 65.Even with the big tires out back and the shinnys up front it stops great.Even pulling it down fron 120 it never has a problem.One guy said it best the car dosnt know where the PP came from.The adjustable can be run all by itself and with factory PP gives you a lot more adjustment.Rocky

I got damaged my original one ( 74 Charger ). Replaced with one of those new replacements iron pieces being sold around, exact pieces to the original one, just some internals are some different. Just last long around 3 years but was working CHARMING on initial moments. Has been told they are having quality issues on half of the units productions ( you tell me )

recently got an Used one from a 77 Aspen. Is working good by the moments. I hope forgett about that issue at least untill we get new better replacement pieces

Disc/Brake units have diff pressure front/rear proportion than Drum/Drum. Not saying won't work, but better if you get it right.

beside that there are 3 kinds of them, depending if SW, Sedan, Coupe, weight of the car. The real name is COMBINING VALVE. Proportioning valve is just a section of the distribution block or combining valve.

Oppositte what ppl and tech says THEY ARE REBUILDABLE, is just that replacement parst are not available. The main problem they get is they break O rings on double action switch piston, and you need to remove several pieces to get that replaced, seats, bushings. Those are the parts are not being sold separatelly. but THEY ARE REALLY rebuildable

Actually they go by many different names ( Combination valve, porportioning valve, self centering pressure differential and porportioning valve, hold-off valve ) depending on the manufacturer and what they do in the braking system. All valves with all the same features won't be the same internally ether. They are tailered to the particular car they are going on ( A body, B- body, etc )- usually the porportioning part in particular. That's where it is easy to run in to trouble when you change from Drum/Drum to Disc/Drum. My suggestion: start with a valve that is as close a match as you can get to what you have ( example = A body disc/drum system ). Then add an adjustable porportioning valve in the rear line if you need to - to fine tune it.

ok thanks everyone..