Introduction: Unlock 4 Digit Cable Lock

Picture of Unlock 4 Digit Cable Lock

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

Picture of 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

Picture of 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

Picture of 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) 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.


jpulkowski (author)2017-06-11

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

SteveB411 (author)2017-05-29

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.

emrz87 (author)2017-04-27

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!

ChrisB850 (author)2017-04-12

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!

cooperhull (author)2017-03-29

It took me 3 minutes!!

ThingEngineer made it! (author)2017-01-06

Thank you so much! My son forgot the combination and lost the little tag the day after he put it on his bike. I was able to figure the combination out with this method using tension from my hands in about 2 1/2 minutes!

AshK19 (author)2016-09-01

Great work .

BynS (author)2016-08-23

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

IgorG36 (author)2016-08-10

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

Good stuff :) Thank you

TommyT28 (author)2016-08-10

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

Col.C (author)2016-07-20

Wow that did the trick in less than 2 minutes.


TedM33 (author)2016-07-09 just beautiful. Took me aprox. 3 minutes , the more tension the quicker it is done. Period. Thanks brother!

EthanH59 (author)2016-06-13

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


this also works with word locks

BorborO (author)2016-05-22

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

AndreaM190 (author)2016-05-08

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.

MishaAustralia (author)2016-04-18

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.

RolandWayneRobertsJr (author)2016-04-11

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

JustinB122 (author)2016-03-05

Right on

DarylO1 (author)2016-02-28


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!

DocHolliday1313 (author)2016-02-17

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.

LeeC38 (author)2015-12-17

This works. The tensioning is the trick. I'm writing the combo down this time.

yama (author)2015-11-02

Found a locked sunlite bike lock at a vacation rental I was at. Now I am a 60 second man in more than one category... Thanks!?

shadnlyd (author)2011-05-06

ding! ding! ding! +1 for use of the word "onomotopeia";

AnthonyT29 (author)shadnlyd2015-09-26

With patience .. it worked.





EricL71 (author)2015-09-25

RudyM4 (author)2015-09-08

Holy S*&% - it worked!!! Thanks for the advise

KoenB1 (author)2015-08-22

This method worked in less than a minute, after I had tried all kinds of combinations for hours. Thanks!

dmm0922 (author)2015-08-08

Had the opposite of this happen to me, the lock was unlocked and apparently the password was changed randomly ... i spun the pins in reverse order until each would click in, finally was able to fix the combo. If it weren't for this post i would have thrown a 20$ chain away

CharlesA7 (author)2015-05-31

Thanks man!!! Forgot my code and this worked

HarmanB (author)2015-05-30

How do you do it.I have no idea.I have a ONGUARD lock and i can't get it

jacksonhorrocks (author)2015-04-14

thanks dude! best guide ive found the tension makes a big difference

JKiley15 (author)2015-03-10

Great instructions and helpful onomatopoeia! Very helpful to have a brief understanding of how the lock works, and the advice about how to "feel" the correct position was right on! After reading your instructions, took me about two minutes to crack my 4 digit Trek bike lock. I found it easier to start with the last digits, as they seem to provide the most resistance, and the clearest indication that I was in the right spot. Thank you!

AndreaF4 (author)2015-02-08

It took me almost an hour and my fingers are sore, but I cracked the combo on my son's two-year old Kryptonite lock using this method. It may have been easier if I had lube.

AndreaF4 (author)2015-02-08

It took me almost an hour and my fingers are sore, but I cracked the combo on my son's two-year old Kryptonite lock using this method. Didn't have lube, or it may have been easier.

SonyaRoweBunch (author)2015-01-14

I just found my old lock exactly like this, and all i done to figure out combo was start with first digit and turn one number at a time, when u try to pull the key out ,it will pull against the digits ,and when the first number is correct it wont tug at it ,but the second number then rotate that number till it doesnt tug at it when u pull it ,and so on and so forth

CyberBuilder1 (author)2014-12-14

I didint work for me I have a really old Krypto lock

ltnemo2000 (author)CyberBuilder12015-01-13

I've heard this from krypto owners before. 2 suggestions:
Dump lube into it. You'll be able to feel fine detail in the tumblers
better if they slide more easily. You may even want to soak it in
mineral oil over night.
2. get a pen and pad and write out everywhere
each tumbler catches. this way rather than having 10^4 possible
combinations, you'll be left with 4^4 which is actually feasible for
exhaustion method.

Hope this helps. If all else fails, smash it with a hammer and send me pics of the internals!

joanna.noah.7 (author)2014-12-17

I can't believe it! This just worked for me! My 16-year-old forgot his bike lock combo and asked if I felt like trying it out. I first spent a few minutes trying some words that I thought he'd find amusing...didn't work. Then I figured out how long it would take trying each letter systematically...way too long! Then I thought of searching Google. I found these instructions and even though I'm not very mechanically inclined, I thought it was worth a try. It took about 5 minutes or less. I wrote the letters down as I thought the sound/feel was different. The dial with the most tension was the most difficult to notice any difference, I wrote down about half the letters! The next three seemed to be more straight forward, I wrote down 1 or 2 for each. So I put the first three on letters that felt right and went through the last letter (the first one I tried) and it worked! I felt like I was straight out of The Italian Job! Now I just need to buy a mini-cooper! Thanks so much for such clear instructions!

chuckdav (author)2014-10-10

it didnt work for me. i have a kryptonite 1018 cable lock.

ltnemo2000 (author)chuckdav2014-11-15

Some locks can be tricky, especially higher end ones. 2 suggestions:
1. Dump lube into it. You'll be able to feel fine detail in the tumblers better if they slide more easily. You may even want to soak it in mineral oil over night.
2. get a pen and pad and write out everywhere each tumbler catches. this way rather than having 10^4 possible combinations, you'll be left with 4^4 which is actually feasible for exhaustion method.

Hope this helps. If all else fails, smash it with a hammer and send me pics of the internals!

TinaC1 (author)2014-10-06

Thank you! You just made me a hero to my 13-year-old. :-)

blows.blows (author)2014-09-09

I bought a 2nd hand bike that had a large 4 digit cable lock - Also onguard, just like the one in the article. I pulled on the cable and felt for the notches. The notches were either there on not so very easy to tell.

I had the lock open in about 15 seconds.. and that's as a first timer!

I am getting something with a key straight away!

CatsConcert (author)2014-09-05

Perfect! Worked like a champ.

I forgot my code to my onguard how do I reset it

mpeddicord (author)2014-04-08

Thank You for this! I fix up bikes people don't want anymore. This had a BELL Kevlar cable, cracked the combination in about 10 mins. Now instead of using my cable cutters someone will have a really nice lock for this bike I'm rejuvenating! COOL!

azharbass made it! (author)2014-03-31

WOW thanks a million! We have a lock that we forgot the combo to for almost 10 years now, and with this 'ible I was able to open it just now! It just took me 2 chairs and a vise-grip (the tumblers were hard to turn) and not even 2 min later it popped open. When you said that it's going to fly apart, I half believed you. I almost got smacked in the face when it sprung apart! It's kind of creepy to think that just anyone with determination can open these things so quickly and easily...

yiucycle (author)2013-10-28

work like charm. found a combination lock and took 5 mins. i just pull the cable apart with my hand and work from right to left. probably wont lock a expensive bike or locks stuff overnight knowing it only take couple mins to unlock.

strain1 (author)2013-09-24

This worked for me!

tbreslow (author)2013-08-16

THANK YOU!!! It's kind of scary how easy that was.

blodefood (author)2013-05-02

Great 'ible! Sounds like it would take too long for a bike thief anyway. But, to someone who needs the lock, oh, so useful!

About This Instructable




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