This has been bothering me for a while. Im not going to write the longest post possible at first, I want to see what others think. Hear me out.
First, drum brakes get an advantage over discs since the friction material is Wedged into the drum. This means for the same force you get additional braking power with drums (to a point).
Second is the amount of fluid sent to the drums. If you had a car setup with drums and an equal car setup with discs the drum brakes would get FAR less fluid for the same braking power.
Third is a valve that is present on disc/drum combo cars. At the moment I forgot the name(Im not referring adjustment of bias). In drum brake vehicles the pads are drawn away from the drum by a spring. Discs are basically in constant contact. Becuase of this a valve is installed that will send brake fluid to the rear FIRST, activating the rear brakes a short amount of time before the fronts. Since the rears need to take up the slack this pause usually means both brakes are activated at the same time.
Now the problems with the drum to disc conversion:
Brake power to the rear is GREATLY reduce for two reasons, the large increase in piston size compared to the drums and the reduced force needed to normally activate drums.
It seems to me that you would need to change the entire "chunk" of components that include the bias/proportion/timing valve in order for it to function correctly.
I would think that some of you have been driving around with basically no rear brakes.
Lets just say for a moment that is not as large an issue as I think. You still have the problem of the rear brakes activating way too early.