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I'm not sure if they're all like this, but my u-lock is a bit loose between the two pieces, the U and the bar. The provided mount snaps very very tightly onto the U, leaving the bar to fend for itself, so when I ride, any little bump makes the lock rattle. I believe the main source of the noise is the loose (non-locking) interface between U and bar; it's metal-on-metal there.

It's pretty obnoxious (and I feel like anyone I pass by must think my bike is broken), so if I have a bag I toss the lock in there instead. Sometimes that's not an option though, so I'd really love to stop the rattle while it's in the mount.

I believe it's one of these:

kryptonite series 2 u-lock

I expect that the little rubber rings are supposed to push up against the bar, and keep things held in place, but mine is loose enough that the right side wiggles around plenty.

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What kind of lock is it? I hear some rattle more than others. – Hugo Sep 6 '11 at 15:10
Yes it's what the rubber rings are for. You just need to slip them down a bit so that they push against the other part of the U-lock when you re-assemble it. @kevin-reid's suggestion to use small cable ties behind the rubber rings is a good one so you don't haver to keep doing this. – Duncan Smart Apr 2 '14 at 9:36
up vote 5 down vote accepted

Anything that will "bunch up" as Mathew suggests should work. You can slip a piece of tubing over the end of the U, or some O rings, or wrap with electrical tape. The object is not to have material actually go into the hole where the U fits, but to "bunch up" at the hole.

Otherwise, you could probably run a bungie from the loose piece to some frame member to keep it in tension.

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+1. I tried a bungee this morning; it helped, but wasn't quite enough. I think the O-ring suggestion is probably good, but I don't have anything like that at the moment. – Jefromi Sep 6 '11 at 15:56
Okay, o-rings are definitely the right idea. The rings that are already on the lock are not actually fixed in place; when pushed down far enough they solve the problem, but they'll eventually migrate back up. Just need to effectively widen them and all will be well. Thanks! – Jefromi Sep 7 '11 at 7:18
Wrap a little masking tape behind the existing rings to keep them in place. – Daniel R Hicks Sep 7 '11 at 11:28

I have a piece of normal inner tube surrounding the U part of my U-lock and that does the trick. It is a bit longer than the actual plastic coated part of the 'U' and bunches up when I close the lock.

I carry the lock on my bike rack or on my rucksack shoulder strap (it has a slot in it), depending on what bike I am on.

With your lock bracket clamping to the 'U' I am not sure if you will be able to get the inner tube approach to work, however, I thought I might share that idea with you to help you improvise a solution of your own.

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Heatshrink SOLVES this problem completely. Go to radioshack, buy the smallest about of heatshrink you can that'll fit, get a heat gun or a lighter or even a blowdrier in a pinch, and say goodbye to the rattling.

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Agreed, very useful on bike accessories where you can get to the end of a tube or bar - but you might need to order online to get a large enough size without buying a huge pack. – Chris H Mar 30 '14 at 8:12
If the heat shrink is going around the end of the u-lock shackle, I don't think Radio Shack will sell heatshrink big enough to go over it. – Batman Mar 30 '14 at 14:01

Simplest way I have found to do this is with a "Bag for life" from Sainsbury's or Tesco, cut a section about 2.5 inches square and push it inside with a pencil. Works perfectly for me. It tends to last about 10-12 months depending on how much you use the lock.

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I've just solved this with two washing machine hose washers (they're the rubber washers that make the seal between the screw part of the hose and the tap, and they cost a few pence). Take the existing sleeves off the ends of the U, put the washers on, put the sleeves back on. Problem solved. Lock silenced. It's like having a brand new bike.

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Gidday and welcome to SE Bicycles. Thank you for your contribution, and I look forward to your future input. – Criggie Nov 16 '15 at 18:53

I have a lock of the pictured design. The rubber rings at the ends of the U would be perfectly good for the job of pressing against the bar to keep it from rattling, except that they're not close enough to the bar to do that.

So I slid each ring out a bit and put on a small plastic cable tie in the space opened between the ring and the covering on the rest of the U, and that did the trick. The rings now firmly press against the bar when the lock is closed, and it doesn't rattle while mounted.

(Actually, it didn't work quite like that for the end with the lock mechanism, due to it and the rotating sleeve; instead I placed the cable tie outside of the rubber ring so that it meets the lock. I'd recommend not doing that and using something narrower to fill the space, if you can find such.)

The advantage of this approach over some of the other suggestions is that you are less likely to get stray material jammed in the interface between the U and the bar, because the supplied rubber rings are thick, close fitting, and otherwise suited for this job — just in need of a little spacer.

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