Kapusta

Here is my situation: I have a dropper seat-post that has an adjustment knob that screws down onto the top of a shaft. Think of a bottle cap, roughly 1" in diameter, but the threads are fine and everything is Al.

It needs to be adjustable by hand, but stay put when riding. In the past it did just that, but the after 15 years, the threads (Al on Al) must be wearing out, and it turns too freely, and goes out of adjustment from vibrations.

So I need something that will keep it put, but still let me turn it by hand on occasion. It does not need to be very tight, just a little.

Is purple Loctite (222) the ticket? I understand that it is a very light holding formula, but after I move the knob the first time, will there still be some grab to it?

I was thinking of putting something like a silicone caulk on the threads, but not sure if that would just end up a mess.

Thanks for any info.

sd5782 

I use the 222 on gunstock screws for spring powered pellet rifles. These are famous for vibrating screws loose. The 222 is nice because is stays a bit gummy and one can retorque on occasion. That being said, I’m not sure it would be ideal for an adjustable bolt that is moved often. I think I may have also read that it is for smaller screws. Might work though.

dsbrantjr

Try Vibra-Tite VC-3. It is intended to be adjustable but help hold threaded parts from vibrating loose. https://www.vibra-tite.com/threadloc...-3-threadmate/

mrv 

Would Teflon tape work? Like the stuff used for plumbing.
It might become a maintenance item. Maybe replace it when you live the chain. But not as often as you inflate the tires.
Could be too much of a hassle.

Kapusta

Actually, I did try that.

The problem is that tape is made for threads that are already rather tight fitting. It took a lot of wraps to get it thick enough to do anything, and at that point it would start shredding and bunching up when I threaded the knob on.

Kapusta

I don’t need to move it very often (in fact I’ll need to move it less once it stays in place) maybe once a year?

WizardOfBoz

The more I read dsbrantjr's stuff, the more I'm impressed. That Vibra stuff looks like your answer.

sd5782 

I’ve also seen vibra tite praised, so it sounds like either would be good especially if seldom adjusted. I had to order online for the 222 as no one seems to carry it. I never use the blue loctite now just the purple. Good stuff

Kapusta

Thanks for that suggestion. That looks promising. How tight does it hold? I was reading reviews and some folks said it holds better than blue Loctite, which is tighter than what I need. But they may have meant that it continues to hold after the bolt is moved.

dsbrantjr

How high is up? I have not done any comparative tests vs Loctite varieties, since they are intended for different purposes. The name kind of describes its function.

FiftySix

Yeah, I use blue Loctite on screws above small set screw sizes. It's still considered a removable screw thread glue that holds well, and most importantly not as "permanent" as red Loctite.

FiftySix

I've never heard of this Vibra-Tite. It sounds like the thing to buy if you don't already have some thread locker on hand. I'll have to look into it for future use, myself.

Kapusta

Gee, I did not think I was asking for the sound of one hand clapping.

I’ll give that stuff a try. Thanks.

leob1

Sounds like a good excuse to upgrade.

Kapusta

I’ve already upgraded to a disposable dropper on my other bike