what causes a caliper to drag

[pred]

Out of no where I stopped last night on a slight incline and noticed that the car didn't roll,
Well lucky I was only about 1/2 mile from home,
The dang front right caliper was seizing up,
what is the general cause?
Car is a 97, 318ti with 150K miles and was always garaged till about 10K ago when I bought it,
Is it time to just buy two new calipers and replace both fronts OR just take this one off, Clean it up and put it back?
Or just replace the offending caliper which I don't like to just replace one,
What would you do?
Peter

[spidertri]

If the fluid gets too old it can trap water in the caliper and corrode the piston. When the pits on the piston get bad enough fluid can leak past the seal and/or the pits can drag on the seal as the piston moves. If the boot is torn, dirt/debris can get in there and jam the piston movement.

It's pretty easy to rebuild the caliper. There is one internal seal that fits in a groove in the caliper and one dust boot. If the piston or bore is bad it is better to just get a new/re-manned caliper. You won't know until you take it apart though.

Boot/seal kits are only a few dollars from rock auto. Even whole Centric rebuilt calipers aren't too much after the core charge.

[Romak]

Improperly greased caliper bushings or dry bushings because the grease is old, will cause them to stick and lock up. Check the caliper bushings and replace if needed. Also check the disk and pads for signs of uneven wear or damage from the stuck caliper, and replace them as necessary. Just remember to get some new grease on there when reinstalling it all and it should last you quite a while. I've also heard of brass bushings as an upgrade but I don't know much about them or where to get them. Maybe someone with experience with those can chime in?