So I Solved the Mistery:
Lots of People have experienced that same problem, Brake Pedal Fade and premature wear of the Front disc brakes ... and some never found the Answer to the Mistery; as you can Read few examples on this Links:
And illogically, I found that the Answer was on the Rear Drum Brakes!!!
Let me explain: The Rear Drum Brake system found on the Second Gen Sephia uses a Ratcheting Cam (Named "Strut" by Kia) that is suposed to take up play as Brake Shoes wear, but definitively, such thing doesn't work at all due to their bad design, and as the rear brake shoes wear, their surface gets farther from the rotating drum and during braking, the rear wheels spin freely while the fronts are doing the braking effort, because the rear brake pumps can't handle well the extra distance without a useful automatic shoes adjuster, that means that the rear shoes are barely "Touching" the Drums under Braking, while the fronts could be at Maximum clamping force.
So, in order to compensate the normal wear on the rear shoes, the car needs Monthly adjustments to the Rear Drum Brakes to Keep said shoes as near to the Rotating drum as possible, and thus means to have a firm & tall brake pedal, and ensure that it has the proper braking power to be Safe.
However, I changed the old Faulty self adjusting regulators with the New ones, only to discover that those are Faulty too ... They're are very Bad designed: some sort of Lifeless Lump that does Nothing to adjust the rear shoes... The old ones and the new ones Never worked; that must be a major design flaw from Kia ... ... Just like the tiny Hole behind the Backing Plate for adjusting the said strut adjusters: Both are Completely Useless, there's No Tool capable to slip thru such tiny, misaligned hole to "Adjust the Adjusters" ... ... nor the Adjuster works as intended.
The Rear drum Brakes on the Second Gen Kia Sephia has another problem related to those Bad designed self "Strut" adjusters: Both sides Never ever wear the Shoes equally, and thus means that the side with more wear is the side that does more braking effort.
In those Rear Drum Brakes of the Second Gen Kia Sephia, I noticed that the Driver's Side, trend to retain the Adjustment for more time than the Passenger's side, which loose it faster; it makes me think that Tire Rotation and its Vibrations might has something to do with that phenomenon: The "Strut" adjusters might suffer from that since they're Weak, while the Old-School style "Star" Adjusters were Stronger.
In Short words, that tendency of the Second Gen Kia Sephia of Loosing the Rear Drum Brake's Adjustment in one side faster than the Other, makes Emergency Braking more Dangerous, since one of the rear wheels could Lock while the other spins freely...
So, the Sephia with Regulated Rear Shoes and the New Proportioning Valves has an Excellent Brake System; the Brake pedal become way more Sensible and the Brake Power is really Good ... but only while the Rear Shoes are Adjusted properly, and said adjustment only last a month ... ... The Self Adjusters are Completely Worthless and Weak.
I need to do Monthly adjustments of the Rear shoes (to compensate their normal wear) in order to keep a firm and tall brake pedal and thus means a Safer car to Drive, and that monthly adjustment means to disassembly the Whole Drum setup, because the tiny hole that they have in the Back (on the Backing Plate) is Useless: I never found a Tool that "Magically" slips thru it and could handle the "Strut" Adjuster to the Proper position... That is another Design Flaw!
Once properly adjusted, the Whole car's Braking Performance is Great.
The only Real Solution for this problem was found by Kia years ago, to install Rear Disc Brakes! ... But only Premium models of the Kia Sephia came with Factory Rear Disc Brakes, and Kia sold very Few of those...
I Started to Search for Rear Disc Brakes on Second Gen Kia Sephias at Junk Yards, Wish me Luck!
Edit: About the Search of Rear Disc Brakes for my Wife's "KiaStein", please read this Thread on the Subject:
Edited by Loyale 2.7 Turbo, 09 November 2013 - 11:00 PM.