I'm on my second OnGuard lock. Their brackets are crap! Sure, they work for a few weeks; but after days of regular commuting over slightly bumpy roads, they no longer hold the lock in place. It flops from side to side; still attached to the bike, yes, but too annoying. I hold it in place laterally with velcro, but this is a pain to manage, and if I tighten it too much the velcro pulls the lock out of the bracket.

Advice?

A pair of Twofish blocks + a Velcro strap. Buy the inline channel versions (Bikeblock) or the cross channel versions (Lockblock) depending on how you choose to mount the lock. The megablock + a additional Velcro strap might work too.

https://www.twofish.biz/bike.html

I have seen complaints about both current OnGuard and Kryptonite lock hangers as NWAS.

Do you have the strap version of the mount? You can try the bolt version; it's much more secure.

If the mount is secured to the bike but the lock flops around, try using rubber bands (you have to replace the rubber when it start to deteriorate).

I think part of it may have to do with the U lock itself. I had an Onguard Brute and just recently purchased an Onguard mini, it looks like the same lock holder for both. It would seem a lock that is about 2-3 times as heavy would need a heavier duty lock holder. But it's probably cheaper for the company to make a universal lock holder.

The problem is that the doohickey on the U part of the U lock that connects to the bracket has come loose. It is entirely unattached to the U. Because it is unattached, the lock swings about freely when it is not in the bracket. This is pretty shoddy construction, in my opinion; it doesn't inspire confidence in the rest of the lock.

The twofish thing -- how many do you need to buy? And, do you have to attach it to the handlebars?

The holder for my OnGuard broke after a few months steady use, just from bouncing around too much I guess. I bought one of the Kryptonite mounts instead, and it's worked well so far. Have more time with that one now than the original OnGuard before it broke, and seems to be holding up well.

Take a look at your lock. The "doohicky" you refer to is held on with a allen head set screw. Retighten the set screw and the lock will no longer swing side to side. The factory tends to leave the set screw too loose. IIRC it takes a 3 or 4mm metric allen wrench to tighten the set screw.

The Twofish blocks are made in a couple of configurations and can be used to mount the lock to frame tubes too if you get the required versions for where you want the lock to mount. You may also need to use a velcro strap to keep the lock from swinging side to side. They are also handy for mounting a small LED flashlight to the handlebars of a bike as a bike headlight. I would get a minimum of two of the inline oriented blocks (Bikeblocks) if mounting the lock to a frame tube. If mounting to the handlebars as the web site shows, which I have no tried, then it looks like three lockblocks would be needed.

I have the heavy-ass OnGuard lock and had to mount the bracket to my top tube to keep the lock from slopping around and the bracket from creaking. This is a hard mounting position to make work for many bikes with top tube mounted derailleur cables, but it reduces the strain on the mounting bracket.

Yes, tighten the allen bolt on the doohickey. I do agree that the mounting bracket is flimsy, I usually carry the lock on my rack or in my panniers.