Bicycle Mechanics - Adjusters self-adjusting!

I have in-line cable tension adjusters (long barrels) on the cables coming out of my Shimano STI shifters (Sora). While the one for the front derailleur stays put, I find that the adjuster for the rear derailleur regularly loosens and requires re-tightening mid-ride.

What could the reason for this be, please?

A. Cable-slippage at the pinch-bolt?

B. Normal-stressing of the cable as you change gears?

Check that the ferrule is spinning freely in the adjuster. If not, turning the adjuster will simply wind up the housing like a nipple seized on a spoke. The vibration from riding will eventually cause the housing to untwist and spin the adjuster back to it's original starting point. I only suggest this really odd sounding problem as the cause because it happened to me. Corrosion built up inside of the adjuster causing the ferrule to get stuck. A new ferrule and cleaning out the adjuster solved the problem.

Thanks guys. It's definitely not cable slippage on the pinch bolt and the ferrules spin freely in the ends of the adjuster. I wonder if the spring inside the adjuster has snapped or something? I'm assuming there is a spring in there?

It's possible that the detents that hold the position of the adjuster are worn. You can try removing the adjuster and filing the grooves deeper to restore the detents.

I don't think there are any detents as this is not an indexed adjuster, just a regular threaded one. I've seen in another thread that people have applied Loctite to the threads to keep them from unscrewing, so I will give that a go...

There should be a locknut that you can use to lock the assembly. It's a small threaded ring at the end.

Most inline cable adjusters don't have a spring. I have the same problem using an inline adjuster with my Nexus internal gear hub. With no spring to provide stable tension, the barrel is free to self-adjust as the bike is shifted and the tension in the cable fluctuates.