Excuse me for butting in to your conversation, but as HMAC300 said, it is not a practical modification. Your brake system was very carefully-designed to have perfectly balanced braking, front-to-rear, and they are all very capable of locking up and causing the tires to skid, which is a bad thing. What more do you want them to do?
Disc brakes are less susceptible to one form of brake fade, and they can be pulsed on and off faster which makes them more effective for use with anti-lock systems. Rear brakes only do 20 - 30 percent of the stopping so they don't get very hot and suffer from fade. If drum brakes respond fast enough for the anti-lock system to be effective, there is no reason for the manufacturer to use disc brakes on the rear.
There is another aspect of modifications we don't talk about very often. If another guy runs a red light and causes a crash, you can be sure his lawyer or insurance investigator will look for any modification to your car. They love to find altered ride height, non-standard wheels and tires, and anything else that could change how the car responds to steering and braking maneuvers. They will convince a jury that you were partly at fault for the crash because you were less able to avoid it, and they usually will be right.
If for some reason you are emotionally-involved with the thought of having rear disc brakes, look at this as an opportunity to go out and buy a car with the options you want. Leave the responsibility for the system to work correctly with the manufacturer.
Monday, January 4th, 2016 AT 4:28 PM