I have a combination padlock that I used on my locker last year, but I have since forgotten the combination. Is there any way to figure it out?
Back in the late 80’s I had a Master padlock whose combo I had forgotten. I took it to a hardware store and they sent in the serial number to MasterLock to retrieve the combo. You had to physically bring in the lock, though, to show that it wasn’t locked to somebody else’s stuff. 
Looks like Master Lock has an official procedure for providing lost combos. Obviously this doesn’t help you if it’s not a Master lock.
You can figure them out. It takes a while. The key is that cheap padlocks don’t require you to be very accurate with your numbers. Often you can be +/- 2 vs. the actual digit. So now your padlock with 40 numbers really only has 8 or 9. So that means there are only 500-700 combinations. Which is a lot, but half the time you only have to do half of them.
(Feynman talks about this in one of his books.)
On some cheap Masterlocks (possibly others as wel) you can play around with the dial and hasp actually “feel” out the combination. I’ve tried it and it works. Specific instructions for this procedure are all over the net.
Yes, I recall it. He had taught himself to crack Yale combo locks when he was younger.
When he was working on The Bomb, he noticed that the vault where everything having to do with the project was locked up at night, he noticed it was a combo lock made by Yale. Curious, he began fiddling with it, and realized it was exactly the same internal mechanism as the ones he cracked as a kid.
So while the retractable steel bolts rendered America’s developing nuclear secrets from all but the strongest physical attack, against intellectual attack they were no safer than a kid’s bike.
When he demonstrated this flaw to his superiors, their solution was to ban Feynman from ever going near the vault again.
I’ve just been sitting in front of my computer and trying random combinations. It’s kind of like working on a rubix cube. But not as fun.
On older locks, at least, you can greatly reduce the number of trials that you have to do by observing these simple rules:
(1) All three numbers of the combination are odd, or all three are even.
(2) The last number doesn’t matter (keep turning the wheel and if you got it the padlock will stop turning).
(3) You can be one number off and still hit.
So all you really need to do is to scan all the even numbers for the first number, and then every other odd number for the second number.
e.g. the trial (2,7) will cover all combinations of (1,7,X), (3,7,X), (2,6,X), and (2,8,X)
You’ve only got 800 possible combinations, really (40x20), and if you can pick trials that encompass 3-4 of them at a time, you only need 100 trials on average.
P.S. note that I have not done this since the early 1990’s. Perhaps padlocks are a little more sophisticated nowadays, but I was able to open two locks using this method, both times it took me less than an hour.
Take a look at some of Matt Blaze’s work for a more elegant than brute force way to crack combination locks.
I know, I know…I’m an ogre for closing this harmless thread.
Sorry. My job. While I’m sure that the OP is only wanting to open his own lock just as many of us have over the years, let him find it on the NET somewhere OTHER than the SDMB. We try to not discuss things that are illegal.
It’s just like smokin’ weed…pretty soon he’ll graduate from school combo-locks to bank vaults, and then, who knows… 
Closed,
samclem GQ mod.
[sub]besides, he already got the answer[/sub]