Why does my ps3 drive do this?

Hi all! I am just looking for a bit of insight. I recently replaced the laser and motor in a PS3 i was given (out of warranty and didn’t want to get rid of an otherwise perfect 80gb ps3 so) I replaced the motor and laser, realigned everything and it works fine which is great. The problem I am having is when I insert a disk and the disk tries to spin. In rotates and stops and rotates and stops but doesn’t fully spool. The weird thing is when I remove the magnetic disc spinner from the top the disk spins and finally begins its full spin and read but it will not do it if the magnet is present upon insertion. Any ideas as to why this may be? Its rather frustrating and I cant seem to figure it out.