stuck calipers

[bill]

What is the best way to deal with a stuck caliper? I replaced all the calipers about 7-8 years ago and now one of them is sticking intermittently. It seems to free itself up while driving but then it sticks again after a couple of weeks (I can tell when I roll to a stop and feel the grab.) Can the offending piston be pushed in/out to free it up? Or is it new caliper time? Thanks.

Bill '74 CS #4310008, webers

 

[x_atlas0]

Have you changed the brake fluid?

Also, rather than replacing the calipers, it is much cheaper to rebuild them. BMW still sells rebuild kits.

 

[Honolulu]

that's odd

It seems strange that calipers, which usually last nearly forever, have siezed in only 7-8 years.

However! You stated the caliper seems to "un-sieze" over a short run. I suspect it's not the caliper but internal failure of the brake line. I can occur that it's easy to step on the pedal and have brakes (due to vacuum assist, of course) but the flex line won't allow fluid to return toward the master, resulting in a "stuck caliper" feeling.

It's my suggestion that you consider replacing the flex lines at the calipers. Stock were about $35 each, last time I checked. Many coupers have gone to the external stainless steel braided hoses. Be sure that the braid doesn't rub on anything if you do this, because the braid will essentiall eat its way through what it touches.

 

[bengal taiga]

What is the best way to deal with a stuck caliper? I replaced all the calipers about 7-8 years ago and now one of them is sticking intermittently. It seems to free itself up while driving but then it sticks again after a couple of weeks (I can tell when I roll to a stop and feel the grab.) Can the offending piston be pushed in/out to free it up? Or is it new caliper time? Thanks.

The short answer to your question, in general, is yes, the offending piston can be pushed in and out to free it. If the cylinder bore is pitted or worn freeing the piston may prove a short lived fix. Sometimes changing the pads can place the piston into an unworn area of the cylinder so that the fix can last much longer. If you really want to know what's causing the sticking, pop the pistons out using compressed air or try using the existing brake system. You will likely find rust, varnish or the like on the piston and you might be able to clean it and pop it back in for a smoother operation. Of course, it is probably just as easy to put in a new "O-ring" and clean the cylinder bore and, in effect, rebuild the caliper.

You did not mention which caliper was sticking, nor how regular your maintenance is, nor the age of you flex hoses. It can be tricky discerning exactly which piston is the lazy one if it is a forward caliper - considering there are four. Each cylinder has only one large rubber ring which, depending upon conditions met, can last for a long time. If the rubber boot around each piston fails and permits water/brake-dust/grit to intrude, things tend to degrade faster than expected. I suppose leaving a car sitting for a long period in a humid garage might also lead to a little sticking.

I agree with Honolulu that older rubber flexible brake lines could mimic or even result in a sticky caliper, but those hoses last a long time too. It is certainly good practice to replace the lines - especially if they are cracked, old or repeatedly left to hold a dangling caliper (I have changed to the stainless clad hoses too). Yet calipers can and do fail. Examine both carefully.

Hth and good luck!