The Differnce Between Do3 - Dot 4 Is Boiling Point Of The Fluid.
Mixing Them Together Should Not Make A Difference,
The Proper Way To Bleed / Change Brake Fluid Is Pass Rear - Driver Rear - Pass Front - Driver Front,
Look Under Your Dash - Pull Back The Carpet, Is It Wet? Find Where The Brake Pedal Connects To The Rod That Goes Thru The Firewall, Is It Wet There? If So Your Master Cylinder Is Bad!!!!!