Calipers stuck closed...

In the past month I have experienced two cars that had the calipers stuck closed, so the brake was basically constantly applied. It wasn't tight enough to keep the car from going, but it was tight enough to notice.

In both cases the pads were worn down pretty bad. It was my brothers car, and my best friend's car, and both of them love to put things off. I imagine that the worn pads aren't thick enough and cause the caliper to have to move too far, can that cause it to do this sticking? Or is it another cause?

Also, when this does happen, does the caliper HAVE to be replaced, or can you push the piston back in safely like you normally do for new pads?

Thanks

the most obvious clue that you have a caliper issue is uneven pad wear, either from one caliper to the other, or from one side of one caliper to the other

You don't state what is the actual issue. Warped rotors? difficulty in wheel rotation? What?

If there is a definite caliper malfuction, you have two choices, replace them, or rebuild them

Binding, corroded, rusted slides can cause the calipers not to retract also.

I've seen sticking pads like this because of other reasons too:
1. piston cocks in bore & won't retract(or extend)
2. Brake line old and won't let fluid out

If it is binding, or just cocked in the bore, and you can force it back in with channel locks or a c-clamp, should that be alright? Or should you rebuild it just in case.

UncleBob:
The problem was difficulty in wheel rotation. My brother's was the front right wheel, he put it off until he grinded his rotor and the garage he took it to put all new stuff in. My friends car was both front wheels (rear wheel drive), you could turn them by hand, but would not free spin after you let go. After we got the calipers off, the wheels free spun a lot more.

In my brothers case, I didn't do the work, so I didn't actually see what happened to the caliper, they just said it was stuck down. On my friends car, the calipers were just $10 each so we replaced them anyway.

its not very clear how much drag we're talking. Its not uncommon for pads to drag a little bit, so that the wheels don't free spin easily. If the pad wear is even on all of them, and the rotors aren't warped, I wouldn't worry about it

If it is binding, or just cocked in the bore, and you can force it back in with channel locks or a c-clamp, should that be alright? Or should you rebuild it just in case.

If the piston surface is corroded or otherwise damaged, it won't seal when pushed back into the bore. If this is the case they'll leak and you'll need to rebuild them (or pay someone else to do it).

But if they push back and work fine then no need to worry. Cracking the bleed nipples open will make the pistons easier to push back.

Brake drag should be minimal.
Compare pads on the right and left of the vehicle.
Compare pads inside and outside of the rotor.
if one pad or one side shows more wear than the others thats a problem.
A frozen caliper can cause premature wear of one or both pads.
When you start to press the caliper back in get a feel for how much pressure is required.
Now open the bleed valve, If the caliper presses in easier the brake hose requires replacement.
If the caliper presses in hard with bleeder open or closed, caliper is bad
Also make sure the caliper slides are moving free, rust free, and lubricated.
There is test equipment out there to test caliper pressure applied, It will allow you to test left and right pressures applied to the pads, and tell you if a caliper is releasing pressure. It is costly About $300 bucks i think.
Anyway If a Caliper is in question replace it, and the brake hose.