Unlock 4 Digit Cable Lock





Introduction: Unlock 4 Digit Cable Lock

About: I'm a Bio-medical researcher stationed in Chicago. Graduate of Loyola University (Chicago) class of 2014.

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.

Step 2: Tension the Lock

I wrapped the lock around a chair (pictured) sliding the cables apart increases tension in the system. you need tension to press the teeth of the shackle against the lock discs. this lets you feel the shape of the discs better and decide when one of the teeth isn't pressed against steel disc and is just hanging out in open air.

Step 3: Rotate the Tumblers

Start with the tumblers that are hardest to rotate first. these have the most tension. tension makes the disc's shapes easier to determine.

Now, there's a couple of things to look for. companies tend to put notches in the discs to give would-be thieves a hard time so you need to look for a union of events.
     -The tumblers will be really hard to turn under tension. When it's all of a sudden easy to move, that's an indicator you have one of the numbers
     -A previously loose tumbler just got hard to move. this means that tension was just taken off of one of the discs and now the shackle's teeth are pressing harder on another disc. 
     -Any consistent response from the lock that is larger when one number is reached than any other. this can be a sensation or a sound. in more expensive locks (like mine) you'll feel (and excuse the hokey onomotopeia) griiiiiiiind...click...griiiiiiind.....jerk....CLICK. the last click (if you didn't guess) was likely the disc reaching it's correct place and a tooth popping into the gap.
     -It's harder to leave a number than it was to get to it. a tooth is in the way of the disc sliding locked again. stop touching it. you've probably got it.

None of these are sure fire on their own. There's a lot of money in making sure you can't figure our how to open a lock without knowing the combo. sometimes there are two numbers on one tumbler that seem likely. write them down and try them with the likely numbers from the others.

Step 4: Have Nerves of Steel

When you get it, you'll be concentrating hard and i can guarantee the lock will fly apart. Its going to startle you. Don't make this remove the idea of setting the combo to something you'll remember from your head.

2 People Made This Project!


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54 Discussions

My son's expensive lock was, wrapped around his frame and he couldn't remember the password. I had to stand with the lock over my shoulder pushing against the bike to create tension. I was absolutely thrilled when and kind of surprised when the lock popped open. I wasn't even looking at the numbers just listening for the click. Thank you so much for this post!!!!

Thanks , I forgot the combo Tony lock, I got it open less than two minutes

Finally did it. Took 15 minutes to open my son's bike lock after he accidentally changed the combination. When it was HARD to go to the next number under tension, I knew the number I was at was probably the right one (largest divet in the lock mechanism), starting from the last number and moving backwards.


1 year ago

I've been watching videos, reading and playing with my bike lock for hours. Read your post and seconds later the lock popped open and scared me!

great instruction. I used two chairs to get the tension and opened an on guard lock in minutes. It had been hanging in the garage for years....brand new!

It took me 3 minutes!!


1 year ago

Great work .


1 year ago

Your a legend... Worked within 2mins. Tension made the clicks loud

You magnificent bastard... Got it in one minute, knowing partial combo!

Good stuff :) Thank you

0005 is what I figured out. Took a couple minutes.


1 year ago

Wow that did the trick in less than 2 minutes.



2 years ago

Beautiful.man just beautiful. Took me aprox. 3 minutes , the more tension the quicker it is done. Period. Thanks brother!

Thanks man took me 1 minute to figure it out :)


this also works with word locks

It worked... And it did indeed open, violently. So violently it hit my face and chipped the right lens of my glasses.

Thanks so much, the tension with the chair did the trick! The lock opened before I got all 4 clicks, so I used a flashlight to align everything inside for the code and it works like a charm now. I was ready to buy a new lock too.

thanks man, the chair trick is brilliant, much better then holding down by feet ;-)

In my case, it was one false hit and one good, on each wheel.

What also helped me to find falce spots was rocking each digit on the wheel backward and forward, to feel the difference.

So, definatly the chair, a pen and paper. Write down spots on each wheel, then try each combination of spots(writing each down to prevent repeat.. ;-) )

Best for all.


Tension IS the answer. Seeing your example of wrapping it around a chair did not quite work, I needed MORE tension. I wrapped this MasterLock 8220 around a pipe clamp as far as it would stretch, after opening the pipe clamps tightener all the way I cut a 2x4 to fit inside the working ends of the pipe clamp. Tightened the pipe clamp stretched the cable as tighter than previous attempts. While it was very hard to rotate the numbers, there was absolutely no doubt when the right number was discovered. After more than several usuccessful frustating attempts I queried Google which led me to Your post, which provided the correct answer. Again I will mention to anyone who may have unsuccessful results even when tried exactly as descibed, the more Tension applied, the more amplified the "clicks" will sound and it will make the wheels much more tight when turning. But there will be ZERO doubt when you turn each wheel and hear the louder "Click".
Thank You for Your post, most helpful


I got an old Kryptonite open by using your method to figure out the last 2 digits were 73 (False openings had me stuck on 84). I was about to start going through all 100 digits to figure out the first 2, but then I realized it was probably a birthday from '73. Sure enough, when I put in 19, the lock opened right away. I think everyone trying to crack a 4 digit lock should start with 19-- just to make sure and then get to work after if that does not start the code. You might get lucky!

I have an OnGuard lock very similar to the one pictured, but newer. I was shocked, this actually worked. The last method listed was the one that worked.