Hey, I just installed some new disc brakes but used some older Shimano Alivio levers. They feel pretty soft when I pull them and I'm wondering if that is because I should use a new set of brake levers that are more "disc" compatible or if any levers will do the trick.
2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
What type of disc brake did you buy? Some have road and MTB versions to be compatible with both types of levers. Newer Alivio levers are convertible between canti and v-brake pull ratios. Not sure about older ones. Undo the brake cables, fully compress the brake lever, and look for a little screw on the bracket holding the cable end. If you find the screw, try removing it and reinstalling in the other position to see if that helps your brake feel.
Once you get that easy stuff out of the way and still have no improvement, you'll need to work on your disc brake installation skills. One thing that I found to be absolutely critical to getting good performance was perfect alignment of the caliper to the disc. In order to preserve the alignment as you tighten down the caliper, you need to tighten the screws in very small increments so as not to twist the rotor during torquing. Getting things perfectly aligned allows you to see the pads as close as possible to the rotor in addition to preventing brake shudder.