Some words of advice regarding U-lock key issues from John Brandt, of the Universities at Shady Grove:
We’ve had this problem and I think rain is washing out whatever lube the manufacturers put in the locks when they assemble them (planned obsolescence?). Eventually, the moving parts of the lock mechanism bind and since the straight keys are inherently weaker that the cylindrical keys, they twist off. Maryland has a lot of rain (40-45 inches per year) so we’ve had this problem with a number of the u-locks we’ve given away and/or sold (all reputable brands) and a good number of other u-locks, as well. The simple solution I’ve found is to put an occasional drop of heavy oil on the moving parts of the locking mechanism that engage the u-bar portion of the lock. Some of the lube may find its way back into the lock tumblers, but in every case I’ve worked on it’s the sliding-locking-bar/pin that was the problem. Simple lubrication seems to prevent the problem from ever occurring and usually fixes it if it does.
• take the lock apart into its two parts
• set the u-portion aside, it’s just an inert piece of metal
• turn the key to make the lock mechanism move to the locked position
• as you turn the key, look into the holes where the u-portion fits
• some u-locks will only lock one side, other will lock at both ends (photo shows a one-sided mechanism)
• drip several drops of machine oil (or chain lube) onto the part that you see moving when you turn the key; this is the sliding-locking-bar/pin that engages the u-portion (see photo below)
• work the key back and forth a few times to get the oil between the moving parts
• once they move smoothly again, the key should no longer bind and you’re good to go
Even with a frozen/stuck u-lock, there is one thing you can try as long as the key isn’t broken off in the lock and unable to be removed. Squirt copious amounts of a thin penetrating oil (like WD-40) down the tiny seams where the u-portion enters both sides of the bar of the u-lock (see photo below). Do it on both sides and don’t be shy with the amount; flood it good. Squirt a tiny bit right into the keyhole, too, just in case. If you’re willing to wait a few minutes for the oil to penetrate, you may find that the key turns again if you start by gently wiggling it back and forth to help the oil penetrate even further. That works on better than 90% of the stuck locks I’ve worked on. I do not use thin oils like WD-40 to lube locks once they’re working again; it washes off too quickly so I use a heavy lube for that.
For preventive maintenance:
• Check your lock whenever you lube your chain
• If the turning key seems to bind or turn stiffly, re-lube those parts (you already have your lube in your hand)
• Prevention is key. If you leave your bicycle outside in the rain a lot, lube the lock more often; the more it rains, the more often you should re-lube the mechanism
• I use a non-greasy lube (Poxylube) for my keyholes so my key doesn’t always come out greasy and stain my pockets ( http://www.locksmithledger.com/product/10288074/sandstrom-products-poxyluber-cp200 ), but I prefer a heavy lube for the mechanism because it doesn’t wash off as fast.
My bikes don’t live outside 24/7 like many others do, but I lube all my locks once a year and I’ve never had a problem with any of my u-locks in over 20 years.
Safety, Security & Transportation Manager
The Universities at Shady Grove