I'd like to ask for your advice, please. I must be doing this wrong and I can't figure it out.

I have two different tail lights on my bike, a Cateye TL LD1000 and a Portland Design Works Radbot 1000. They're mounted on a kludge PVC frame, which is connected to the back of my rack. (Surly LHT, btw)



Both lights will rotate on their mounts so that they face down. The hardware stays in the right place, but the grip plates that the screw goes through jiggle loose on the ride.

I have really tightened the bolts. I have used the thread-locker stuff on the bolts. I have poured Elmer's Glue into the grip plates, and that does work for a while but then it resumes the rotation-on-vibration.

Since these lights are from two different manufacturers it must be me.
I'd really appreciate any advice.

Try putting a toothed washer/lock washer in between the grip plates.

This is what Im thinking of:

Good suggestion. If that doesn't work, use lock washers.

It sounds as if you moved the lights when the bolts were a little tight. Every time this is done it removes more and more of the little plastic ridges that make the bracket stay in place.
I also have accidentally swapped the bracket parts between two different lights when working on more that one light at a time. This would do it too.
The washers will work just fine.

If you damage the bracket for the radbot, I have at least one unused bracket, maybe
even two or three.

edit- I may have brackets for the Cateyes too. I always save brackets.

edit, no don't use a nylon nut. You don't get the light off.

I had the same thoughts, thanks for typing them for me.

Yes, OP, you've either damaged or assembled them improperly.

I used the same Cateye taillight for over a year and it never slipped down once.

For the OP. For the record, I have also stripped out the ridges on a bracket.

I use duct tape to hold mine in place.

Assuming the plastic ridges are smooshed or worn, you can try using thick superglue (cyanoacrylate) on them. Put some on the surfaces, assemble and tighten it, and let it cure.

I have used Finish Line Fiber Grip on some parts where the two plastic parts slip all the time such as the joint on the Mirrycle. It helps keep the mirror from rotating on every pothole, but the stuff only last for so long (6-8 month) before I have to loosen the joint and put some more of that stuff in between the joint.

The Internal or External tooth lockwasher should work as suggested. They might leave a little indentation on the plastic which is not really a problem unless you use a split lock washer. If you find the washer still slip, then try some of the fiber grip alone or with the lock washer.

If you don't mind not being able to move it later, superglue works well. Just get it into the position you want, then add a drop or two of superglue, and hit it with the kicker if you've got it.

Thank you to all, I really do appreciate it. +Karma to you!