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Some time ago, I stuck a U-lock on my bicycle for safe keeping, on the top tube below the seat. It's annoying when riding, and I'd like a way to remove it. I've lost the key some time ago, or I would have removed it that way. Preserving the lock is optional. What would you suggest?

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Ideas:

  1. If you still have any of the original paperwork or packaging, look for a lock code/number, you might be able to order replacement keys.
  2. Take it to a bike shop and ask. They might have the right tools. They likely do this every once in a while
  3. A machine shop is sure to have tools capable of doing this
  4. The local police department will have the tools or be able to refer you to somebody that does (they have to deal with removing abandoned bikes)
  5. An angle grinder, or other rotary cutting tool with a metal-cutting disk
  6. Hacksaw (electric preferably. Maybe an extra blade)
  7. Big bolt cutters
  8. could you close the lock without the key? Cut away any rubber and slide a shim made from an aluminum can down to release the latch
  9. Is it a cheaply made lock? Might be able to just beat on it with a hammer until the latching mechanism falls apart
  10. a small car jack. Most u-locks lock on one side and connect with an L on the other, so bending the U open will release it

For the tool based approaches, I would be very tempted to work out some way with a vice or two to hold the lock and bike steady, to minimize the chances of damaging the bike.

Thieves also use leverage based attacks, but I believe those risk damaging the bike.

And, of course, having proper proof that the bicycle is yours is a good idea, too, since all those attempts to defeat a lock look suspicious.

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    I'd only add to this, bring it to the police station. They should have the tools to cut off a bike lock. (I'd also bring along documentation that shows ownership of the bike, just in case.)
    – Goodbye Stack Exchange
    Commented Nov 10, 2011 at 6:40
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    Angle grinder is probably the best choice, with the least chance of damaging the bike. Bolt cutter might or might not work. (Or, if it's a Kryptonite, just use a Bic pen.)
    – Daniel R Hicks
    Commented Nov 10, 2011 at 12:34
  • link to video showing Bic pen technique: youtube.com/watch?v=LahDQ2ZQ3e0
    – Rory Alsop
    Commented Nov 11, 2011 at 10:43
  • I would try the car jack first, machine workshop second
    – heltonbiker
    Commented Nov 11, 2011 at 13:21
  • @heltonbiker: I put the jack last since it seems difficult to do without damaging the top tube of the bike, and might be difficult to find jack that will fit inside the lock.
    – freiheit
    Commented Nov 12, 2011 at 0:28
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I figured out a way to do it which was actually fairly easy. This only worked because it was in my garage, trying to steal someone's bike like this would be crazy...

I took a hammer, and pounded on the bar. The first thing that happened was the plastic broke away. I kept pounding on it, until the lock just fell apart. It took about a minute...

Note to self, don't buy a cheap lock next time...

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  • Sometimes there are youtube videos on how to unlock the cheap locks with things like toilet rolls too.
    – Colin Newell
    Commented Nov 10, 2011 at 13:24
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    I'm really curious what brand of lock it was that was quite that easy to defeat.
    – freiheit
    Commented Nov 11, 2011 at 2:28
  • It was Top something, Toplock maybe?
    – PearsonArtPhoto
    Commented Nov 11, 2011 at 3:57
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A bit late now, but for the future it's worth knowing that it's possible to order a replacement key for most locks.

You'll need the serial number which is usually on the key or might be separately in the packaging (it's not written on the lock itself for obvious reasons), so you need to make a note of that somewhere and keep it in a safe place.

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This works with almost any type of lock: Cost $0.

  1. (optional) lubricate the lock with all purpose oil or graphite powder. the lighter the oil the better.
  2. get a similar key that goes in. just find a friend with a ulock that still has the spare key.
  3. get the spare key and file down the tallest teeth so that the key is a series of the lowest teeth
  4. insert key and keep applying pressure as if you were going to turn it to open the lock, and releasing the pressure. keep doing this over and over during next step.
  5. get a small hammer and gently knock the key. as if nailing it INTO the lock. several times. keep doing it. does not loose your temper and apply force. gently.

eventually, the key will turn!

the Technic is called Bump Key.

Bonus information: lock-picking is a nerd past time with several tournaments in the hacking community. If you want to learn more look for the MIT guide to lock-picking. Yes, that MIT.

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    Doesn't the bump technique only work if none of the teeth are higher than on the right key? I thought it was usually done with a key with all the teeth set low (or filed down)...
    – freiheit
    Commented Nov 12, 2011 at 19:13
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    Bumping mostly only works on locks with springs (especially pin-tumbler lock used on most doors). Many bike locks are designs without springs since those hold up better in the outdoors. I believe my U-locks use a disc tumbler lock, which is a design bumping doesn't work on. In other words: only works if key is a blade with teeth on one edge.
    – freiheit
    Commented Nov 12, 2011 at 20:34
  • both of you are correct. sorry, i'm not a fan of bump key as it require to carry more stuff than picks. vote me down because of what @freiheit says. the chance a random key will work is pretty slim.
    – gcb
    Commented Nov 12, 2011 at 21:07
  • updated the technique
    – gcb
    Commented Nov 18, 2011 at 6:05
  • Bump keys are rarely possible to use on a U-lock. Bumping knocks the pins upward quickly, when combined with twisting pressure the pins will lock in place and allow the cylinder to turn. Most U-locks, even ones bought at walmart, use a key that compresses pins inside a channel in the key, which makes it much more difficult. ANY lock that is vulnerable to bumping is much easier to use a pick-gun or electric rake on.
    – fightermagethief
    Commented Feb 18, 2016 at 20:58
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We all lock ourselves out of something at some point. At times it can be useful to respect friends 'with links to the criminal fraternity': cheaper with fewer questions asked when it comes to getting cars opened, D-locks removed and house windows opened.

@Daniel R Hicks See this:

http://www.youtube.com/watch?v=0hsM88Wx8QQ

Picked with a biro in a matter of seconds, not even 'Kryptonite'.

Some locks used to only come with half a dozen or so key variations so the security was assumed anyway. With manufacturing outsourced to the Far East any brand, no matter how 'reputable' can have locks on sale that are not really that clever.

Sounds like you actually had a 'fake D-lock'. Even the big makes foist these on the public, where the barrel is some bent tin inside a chunk of plastic. Those can be opened with a moderately sizeable piece of wood.

Even if it was a real D-lock, have a look at how it would respond to the disc-cutter:

http://www.youtube.com/watch?v=4XTYEcQAurs

What is that, 5 seconds?

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