After a getting a flat on Tues I finally retired my old tires and threw on a pair of Schwalbe Marathon Supremes. Had my bike upside down for the process. When I finished, I noticed the rear wheel brake noticely had more give than before. I have the squeeze the lever all the way to brake now.

I can't figure out why how this could be. I've never had to do anything with my brakes since buying the bike nearly 2 years ago. Any ideas?

I've heard that certain brands of MTB hydraulic brakes MAY leak if stored upside down. I don't remember which brand but I think you need a flush/refill kit. I haven't done this personally yet, and I'm wondering how long I can ride until I have to.

2 years w/o service? About time to have both brakes bled. You can buy a kit to DIY, or take it to a local shop to have it done.

You may have gotten air in your line while it was upside down.
A good bleeding is in order.

Thanks for the replies. You're probably right, I'm due a service anyway and the front pads came from the mfg contaminated so they're noisey.

But interestingly, after standing upright all day at work it was back to normal for the commute home. Maybe there must be some air in the reservoir which made it's way in to the lines while upside down in the cold. I did squeeze the brakes to ensure the calipers were aligned when I put the wheels back on (still upside down).

At least now I have the option to procrastinate although I take your point I'm probably due a service.

Certainly had to be air from the reservoir and when you flipped it and pulled the handle you pushed the air into the lines. Standing upright at work allowed the air to return to its highest point.

Being upside down can temporarily do that to hydro brakes. It's happened a number of times with my Avid Elixirs. They go back to normal. That said, after two years, a good bleed is probably still in order.

DIY bleed is pretty simple (for my Shimano anyway) and the local shops charge a lot. Same money would buy you enough fluid to last for years.