My rear disc brake developed a strange feel on a ride this morning. It started getting a "catch" feeling in the first 1/2" of lever movement and smooth after that—-at the same time, the rear brake isn't engaging well—have to use more lever pressure than usual to get full braking. The pads are only a month old and only sightly worn— there is even spacing on each side of the rotor and no dragging/rubbing.
Any thoughts? I can do most adjustments/repairs, but brakes, for some reason always seem difficult for me.

Sounds like you may have a sticking caliper piston to me.

I just took a close look and I think you are right about the sticking piston. One side of the caliper is closing and the other not. Any ideas on a way to loosen a sticking/stuck piston outside of replacing components?

Hold the moving one in and use lever pressure to free up the other one – when it has moved out clean it and lube it – mineral oil for shimanos – and then work it in and out a few times

Of course it must be a figment of your imagination – nothing goes wrong with shimanos -everyone knows that.

Good luck attempting to get spares for it – not many bits are available

Hey Tandem, thanks, that did the trick and freed up the stuck caliper. I am assuming it was just fine dust that had it gummed up. Riding here in the SW US, dust & sand is the biggest culprit–we don't have to worry much about wet conditions.

I use copper grease to help lube the brake caliper pistons. Works for me anyway 🙂

Edit: Oh and also a spray can of switch cleaner is a good solvent to clean brake stuff up and remove any small amounts of stray brake fliud, oil, grease or thumbprints

Check the rivets that hold the disk to the spider for play.
I've had 4 disks work loose so far!

to rectify get a hammer and …………… re-rivet!

Nainosliw – Member

I use copper grease to help lube the brake caliper pistons. Works for me anyway

I would never use it in this way – use something you know is specifically designed and safe to do so. Copaslip is gritty

Edit: Oh and also a spray can of switch cleaner is a good solvent to clean brake stuff up and remove any small amounts of stray brake fliud, oil, grease or thumbprints

Again – be very careful – some switch cleaner contains lubricants and I don't know what the solcvents will do to the seals.