>1.  Why does an all drum hawk need a check valve in the master
>cylinder? Is the check valve only for the rear drums?  If so, what
>about the front drums?

>> the check valve maintains fluid (under very low pressure) in the lines and
wheel cylinders, other wise you would have to pump the brakes up (like a
hydraulic jack) every time you wanted pressure.

>2.  Why does everyone recommend defeating the check valve when
>re-equiping the hawk with a front disk conversion?  It seems like the
>rear drums would still need some kind of pressure buildup.  Does this
>mean that if I bought a new master cylinder for a hawk with front
>disks, the master cylinder would not have a check valve?

>>>>Drum brakes use actual springs to return shoes (needing 10 lbs. line
pressure) discs use a rubber boot (needing only 2 lbs. line pressure) if you
use 10 lb. check valve in disc sysytem brakes will drag (actually partially
applied).



>
>3.  With dual cylinder conversion kits, a 10# rear and 2# front are
>recommended.  Again, please explain why. 

>>>> see answer #2 (old style single master cyl. had check valve inside, new
dual type has check valve in combination prop/check valve)

>Does a proportioning valve
>change the effective settings of the front and rear check valves.

>>>> a "prop" valve allows "XX" amount of pressure to go to all wheels, then at
a certain point restricts pressure to the rears to maximise braking effort
(fronts do approx. 60%) and minimise rear lockup when weight shift occurs
during braking.
( example: a vehicle with 150 lbs. pressure on the brake pedal will result in
approx. 1800-2000 lbs. on front disc pads and 500-900 lbs on rear shoes)

I hope this helps.