How to Crack a "Master Lock" Combination Lock

How to Crack a "Master Lock" Combination Lock
If you’ve forgotten the combination to a Master Lock combination lock, you have a few options. If the lock isn’t locked onto anything, you can make a photocopy of the serial number and send that to Master Lock for the combination. If, however, your lock is attached to something, you can break the lock, call a locksmith, use a shim, or figure out the combination. Of these options, only the last two will leave you with a usable lock without emptying your wallet. Unfortunately, there are 64,000 possible combinations on a standard 40 digit Master Lock. With this method, however, you can quickly narrow that down to 80 combinations, a workable number to try if you’ve got the time and the inclination to give it a shot.

Look for the Master Lock brand. This method only works with Master Lock combination locks, and may not work with all of them. It is rumored that Master Lock changed the combination algorithm on some of the newer locks, in particular those with serial numbers starting with the number 800. Some people, however, have reportedly had success cracking these with this method, too, so it may be worth a try. Check the discussion page for this article to check which serial numbers others have had success with.

Turn the lock’s dial clockwise to zero. It is a good idea to turn it at least three rotations first, just to make sure it’s clear. Apply steady tension to the shackle and turn the dial clockwise. The shackle is the u-shaped part of the lock that goes around whatever you’re locking. To apply tension you can either pull the shackle up while holding the lock, or you can pull the lock down if the shackle is locked onto something solid. Turn the dial slowly as you apply tension. If you can’t turn the dial at all, release the shackle and turn the dial clockwise just a number or two and then try it again. Find the first sticking point.


As you turn the dial clockwise with tension on the shackle, you will come to a point where you can’t turn the dial anymore. Make note of where it stops. Sometimes it will stick right on the numbers, but sometimes it will be between the numbers. If so, record the number to the half (e.g. 22.5, 7.5, etc.). While continuing to apply tension to the shackle, turn the dial as far left (counter-clockwise) as you can. Make note of where it stops. Now you have a sticking "range." (Note: Some 800XXX locks have a two number range [e.g. 28-30], this sticking point is the last digit of your lock.)

Determine the sticking point by finding the number that's in the midpoint of the sticking range. A range of 4 and 5 would have a sticking point of 4.5. A range of 22.5 and 23.5 would have a sticking point of 23.
Release shackle tension and turn the dial slightly past the sticking point. Turn the dial clockwise about one number from the sticking point in order to allow you to "escape" that sticking point. Reapply tension to the shackle and continue turning the dial clockwise to find all the sticking points. You should find a total of twelve sticking points in one complete turn of the dial. Write them down. Find the third number of the combination.

Look at your list of sticking points and eliminate all those which are not whole numbers (i.e. cross off any number that ends in .5). You should eliminate 7 of the 12numbers with this step. Of the remaining sticking points, choose the one with the unique digit in the "ones" position. Four of the remaining five numbers will share the same number in the "ones" place, so for example, if the numbers left on the list are 4, 14, 24, 27, and 34, the number 27 is the only one which does not have a four in the "ones" place. This is the third number of the combination.


Find the magic number. Divide the third number of the combination (27 in this case) by four and write down the remainder. In this case 27/4 = 6 remainder 3. Remember we are only concerned with the remainder, which will always be 0, 1, 2, or 3. Write down the magic number (3 in this example). Find the possible first numbers of the combination. Add 4 to the magic number (3). Write down the result (7). Now add 4 to that and continue adding 4 to each resulting sum until you have gone completely around the dial once. Write down each of these numbers. Thus, for the example above the numbers would be 3, 7, 11, 15, 19, 23, 27, 31, 35, and 39. One of these numbers is the first number of the combination. (NOTE: For some 800XXX locks this will be the second number of the combination. The next set of numbers will be used as the first)

Find the possible second numbers in the combination. If your magic number is 0 or 1 then add 2 to it, otherwise subtract 2. Since our example magic number is 3, we subtract 2 and get 1. Write down the answer and add 4 to it. Now add 4 to each resulting sum until you have gone completely around the dial once. Thus, in the example, the numbers would be 1, 5, 9, 13, 17, 21, 25, 29, 33, and 37. One of these numbers is the second number in the combination. Cross out the numbers (the possible 2ND numbers) Plus or Minus 2 [25 & 29] from the third number of the combination[27].

Figure out the correct combination by trial and error. You now know all the possible first numbers [3, 7, 11, 15, 19, 23, 27, 31, 35, 39], all the possible second numbers [1, 5, 9, 13, 17, 21, 33, 37], and the third number [27]. You’ve just narrowed down 64,000 combinations to only 80. Now try each combination until you find the correct one. If you’re lucky, you may need to try only a few but then again, you may need to try all 80.

After cracking just one lock, the system becomes much easier to understand, so hang in there. If you’re in a hurry, you don’t need to calculate the possible first and second numbers yourself. Once you’ve figured out the third number, you can save time by using a special computer application to determine all the possible combinations. See the External Links section below.

Though not necessary, you may find it helpful to write out the combinations methodically so you don’t forget which ones you’ve already tried in the middle of the next step. Thus, you could make a chart with all the combinations (3-1-27, 3-5-27, 3-9-27, etc.)

This will work only if you get the 12 numbers: 7 decimals, 4 integers with mutual "ones places" and 1 integer with a unique digit in the ones place.
Only consider proceeding with this method if you enjoy a challenge. Otherwise, cutting off the lock and buying a new one makes more sense.

If your lock has a keyway on the back, you can also drill a small hole next to it so that you can view the tumblers. After you align the tumblers, and determine the unlock code, you can seal the hole with a two-part epoxy. Some times the sticking points for finding the 3rd number are not exactly on top of a number or between two numbers.

In this case:
1. turn clockwise (right) the first of the 12 sticking points from 0
2. continue to turn clockwise to the opposite side of the dial
3. turn counterclockwise (left) back to the first sticking point from 0
4. pull up on the lock and turn the dial left and right in the small sticking area and right down the exact range. (e.g. 2.75-3.5)
5. repeat this 4 more times for the numbers 10 more from eachother. (e.g. 3, 13, 23, 33)
6. now do steps 1-5 for the second sticking point past zero
7. do the steps again for the third point past zero.
Each set of numbers will all have the same range. For example, one group may be .0 to .0, another .25 to .75 and the last .5 to .25 on either side of the sticking points.

The third number of the combination is the one that doesn't fit within it's group.On my lock, it was also the one that had the most play in the range (5.25-6.75, 15.5-16.25, 25.5-26.25, 35.5-36.25). So my third number was the 6. If you notice, those 4 ranges are all for numbers with 6 in the ones place, had I followed the directions above, I may have ended up trying for a different number! Steps 1-4 aren't required but it seemed to give me some better results. Some numbers seemed to slide one way or the other by .25 if I didn't do steps 1-4 for every sticking point.

Do not use this technique to crack someone else's lock without permission of the owner. If you do that, you are breaking the law and could be prosecuted accordingly.
When finding the sticking numbers, be very precise. Otherwise you won't get the correct numbers.