It feels like something inside the machine catches and then releases causing a loud bump noise from within and a slipping of the stairs. i tried WD -40 over a range of parts that move and the problem got worse instead of better
Exercise & Fitness - RTO - Tectrix Personal Stair Climber
Answers & Comments
I'm not familiar with which part would fail, but I will tell you that generally, when you spray WD-40 and the problem gets worse, it's because a degenerating bushing got worse with the application of the WD-40. The unit will have to be disassembled to be able to inspect any gears and bushings inside the stair drive mech.
I just ran across this answer from another tech here on Fixya, and perhaps it will solve your problem:
http://www.fixya.com/support/t4955118-stairmaster_freeclimber_4400pt_fix
Good luck, and hope this helps.