Proportioning Valves?

Actually what everybody calls a proportioning valve is really a combination valve. Proportioning valve is the wrong name. Not sure where that got started at but that's what alot of people call it. Just like calling the parking brake an emergency brake I guess.

Anyway if you can get the combination valve off the Duster you got the disc setup off of you'd be well off. The combination valve also has another funtion to it that slows down the action of the disc brakes slightly because they react faster than drum brakes so all 4 brakes apply at the same time called a metering valve. You can use your original valve and it'll work but you'll get a nosedive effect because of the missing metering valve. I believe the disc combo valve had a residial pressure valve in it for the rear brakes also but not positive on that. If you can't get the original valve you can add these pieces if your not happy with the performance with it once you get it together.

Here is a link with alof of good info all about brake valving you might find interesting.
http://www.mpbrakes.com/mpfaqvalving.htm