i have a 94 sentra se-r. my car front brakes locks up very easily and cause the car to slide when im making an abrupt stop. it seem as if the back brakes are not working. *** could be the problem? proportioning valve? does my 94 se-r have ABS? also does anyone have the part numbers for the proportioning valve? and ABS module for a 94 se-r?

Go to courtesy nissan or similar website for the part numbers. Some B13 SE-R's had ABS and some didn't. Jack the car up and hold the brake to see if the rears at least attempt to grab if you think they might not be working. You will need someone to help with this unless you use something to press the brake down for you.

looking at the rear rotors , its like theyre rusted and not used compared to the shiny smoothe front ones.