On my bike, how do i reinsert disc into disc break mechanism after removing tire and rim.?

After repairing a flat on my bike's rear tire, I cannot get the disc to go back into the disc break mechanism. I'm stuck without a bike until I can get it back on. I've never worked on disc breaks on bikes so I don't know names of break parts or where they are located.

Hum...

Are the brakes pads stuck together? The brake pads are inside the brake caliper which is affixed to the frame of the bike sort of opposite the rear derailleur. Looking into the back of the brake caliper, you should be to see the two pads, between which the brake rotor fits. You should be able to very gently slip a narrow screwsriver or knife blade between the pads.

The brake rotor (the round metal object affixed to the wheel should simply slip between the brake pads as the wheel axle fits into the dropouts. It shouldn't be a big deal, however, you sometimes need to jockey things around a bit in order to get everything aligned.

A rear wheel often requires the most tweaking due to the fact that you have the chain meshing with the gears. It is usually easiest to get the rear wheel back in place if the rear derailleur is shifted to the furthest out position (highest gear, smallest cog.) Only hook the chain onto the smallest cog as you line the wheel up. This gives you the most slack in the chain.

If you have hydraulic disk brakes on your bike, you never want to squeeze the brake lever when the brake rotor is out of position. Squeezing the brake lever without the brake rotor in place will force the brake piston to be driven out of the brake cylinder, and/or dislodge the brake pad. If this happens, you may be able to coerce the pads back into position, but more than likely the brakes will need to be bled. If this is the case, you should probably take the bike to your local shop and have them show you what to do.

Hope this helps.