Okay, I'm back
I have boiled down the method so it is now generic, and very fast.. (tested on several of my locks)
Step 1: Collect underpants
Step 2: ????
Step 3: Profit!!
In more detail:
Dudley locks have three code-wheels inside them. When you pull up on the shackle, the latch presses into the stack of wheels. Each wheel has a deep notch in it (real gate). If the notches are lined up together at the right place, the latch is able to move in, and the lock can open. Also note that the front wheel is at the very front of the pack, and attached to the dial.
The two rear wheels (corresponding to the first and second numbers of the combination) have two false gates, notches that are not deep enough to allow the lock to open. The front wheel has 9 false gates (making 10 total gates).
If the rear wheel is aligned so that the latch fits into a gate (real or false), then pulling the shackle up will make the latch press into the second wheel, making it difficult to move/manipulate. If both of the first wheels are aligned, then the front wheel will be difficult to move.
We can use this fact to quickly locate all the gates:
I. The first number
Pick a number to start with, say 0. Spin the dial clockwise twice to pick up all the wheels, and point it at 0.
Spin the dial counterclockwise
to at least past 6 (that is, until you hear/feel the second cam from the other side). Pull the shackle up and try to move the dial farther CCW
. If it feels 'scratchy', it means that the 3rd wheel is on a gate. If you can't move it at all, it's possible that you ran into a separator between the gates on the top wheel. Release the latch, move the dial another ~3 points CCW
and try again. If the CCW
motion with the latch pulled is free, then 0 is not the right number.
Release the shackle and spin the dial CW
, stop at 3.
Repeat steps (b)-(c), adding about 3 notches every time, until you find a gate on the first wheel. This is the first number (with 50% probability)
II. The second number
Now, move the dial CCW
about 3 points, then return it several points back (5-10, far enough not to disturb the new location of the second wheel). Pull the shackle and wiggle the dial within the gate. If it's easy to do it, the second wheel is not aligned correctly.
Repeat step (e), moving the dial about 3 more points CCW
each time, coming back, pulling the shackle, and wiggling the dial until it becomes hard to move ("scratchy"). Once this happens, it means that you found a gate on the second wheel
III. The last number!!
Now, move the dial CW
one more gate worth, pull the shackle, wiggle.
Continue moving like this, until you find a spot where the dial wiggles free. This is the last number, guaranteed
If the first two gates you picked were real, the lock should open at this point!
If one of the first two gates was false, the dial will wiggle free in one of the third gates, but the lock will stay locked. If this happens, continue at step (f), to find the other gate on the second wheel. Once you find it, come directly back to the third number and try your luck again
If you were born on Friday the 13th, then the gate you found on the first wheel was false. Come back to step (d) until you find the other gate.
Now you're done, and the lock is decoded for sure!!
(don't forget to check which of the gates on the second wheel was real)
I hope the instructions are easy to follow. They are verbose, so the description is long, but the steps are very quick to do..
The worst possible scenario that I can think of is decoding a lock with a combination like 05-10-05, with false gates at 00 and 05, respectively, starting from 10 and going clockwise.
In this case, you will need to perform 52 shackle pulls and you'll make about 47 full rotations worth of the dial.