My brother's friend found my 6ft On Guard cable lock and promptly reset the combination to something he was too lazy to remember. so I cam up with this method to find the lost combination and save the world (my world)
This is the semi-hard way. it's not the exhaustion method (trying every possibility) but it takes a little brain power and reasoning.
I know there's a lot of stuff on line about how to unlock a cable lock but these methods only work for the drug-store variety of locks that have low tolerances and a lot of wiggle room. (i'll explain why later) This one works on the nicer kind. the ones that have half inch braided cables and much tighter tolerances.
Don't try to use this to steal a bike. It won't work. you can't put enough tension in the system to feel the shape of the disc using your muscles while rotating the tumblers. If that's your reason for being here, kindly piss off.
Edit (2014): I have since retired this lock. After moving to the Roger's park 'hood of Chicago, it has become rapidly apparent that cable locks are not only easy to crack but easy to cut. Kryptonite's higher-end locks still prove to be beyond my ability to crack. their tolerances are tight making the lock seize under tension. the only way to open one seems to be through exhaustion. anyone good with arduino want to make a robot?
I now use a keyed on-guard U-lock.
Step 1: Understand what's inside
inside there are four rotating plates with a notch the shackle to slide through. When you scramble the lock, the plates slide to block the shackle from coming out.