Brake caliper dragging

[frankc]

Today I noticed that the car wasn't rolling quite as freely as is should when coming to a stop. Upon checking the wheels, I discovered that the right rear caliper was significantly warm, while the others were cold to the touch (it's winter here). This is one of the reasons I don't like slider calipers, they never seem to do well in the nothern winters. I can't believe BMW even puts these types of calipers on an 'M' class car - I would expect dual piston at a minimum.

Anyway, does anyone have any magic trick to keep these things moving freely after dissambling and exercising the caliper?

thanks

[frankc]

Update:
The sliders on the caliper were fine - no corrosion. And exercising the caliper did not help either.

So, I picked up a caliper rebuild kit and pulled the caliper apart. I found the source of my problem to be the dust boot that attaches to the end of the piston. The boot fits into a channel in the caliper bore and is held in place by the piston. In my case, part of the boot was not seated in the channel, thus being squeezed between the piston and cylinder wall. I doubt these brakes have ever been rebuilt before, and it was obvious that the boot had been like that for a long time since the channel where the boot was displaced was completely filled in with dirt. I'm guessing they were improperly assembled from day 1.

The good news is the car rolls *very* freely now. It feels like I've gained 5-10HP. I'm curious to see how much better my gas mileage is as well (with the price of gas these days, it can't hurt).

One hint, when reassembling the caliper, be sure to have compressed air handy. You'll need it for getting the boot over the piston. A strange process that I would have never figured out without the help of the instructions that came with the kit.