Q:

Why is the bottom half of my 35mm photos black? 

So this isn’t in all my photos only some, I    Use a Pentax super A1.  The bottom half of the photo sometimes comes out as nothing.  This is annoying and unpredictable.  I have read that  It may be the shutter, so would using it at a slower shutter speed maybe help?  I usually adjust apature manually and let the camera decide the shutter speed.  Could I maybe not go quicker than 250?  I just cant remember which shuttter speed the photos that came out okay were taken at/#. 

A:

The example photo appears to be the result of a malfunctioning shutter mechanism.  It most likely need to be replaced.  If your camera is not worth what a shutter replacement would cost, then it's time to consider a new (or different used) camera.