Internal flexible brake line failure: it finally happened to me.
 

Symptoms were strange: sometimes the brakes acted normally but sometimes I had the vague sensation that the pedal was going a little further towards the floor on brake application. Sometimes at stoplights I noticed when taking my foot off the brake, the car would hold brakes for perhaps 5 seconds then start rolling if there was a grade. :confused:

When the brake pads finally disintegrated I put new pads and rotors on the front... test drive OK... longer drive NOT OK! :mad: One caliper was dragging enough to make a stink. NOOOOOO! Not my nice new parts!!! :mad:

Disassembled caliper and all looked well, at least from a seizing standpoint. Took the flex line off and couldn't blow through it. Easily blew through a new line. Voila.

Old line completely lacks external visible signs of failure. No cracks, weatherchecks, oil contamination, hernias, nothing.

It thinks it looks innocent but I know better.
http://s146.photobucket.com/albums/r...1331945894.jpg

Good detective work!

Educated guessing + process of elimination! :thumbup:

I also did a new thing in sanding some grooves out of the phenolic plastic caliper piston. That thing is probably OEM so it is 20 years old. I went online to see if there was any prior art to sanding grooves outta plastic pistons but found nothing. I decided that sanding had everything to gain and not much to lose, so that's what I did. Came out looking very nice and it seems to work well too.

I once also had one flex line failure and saw some of those strange symptoms. Had a dragging brake that would release slowly after not pressing the pedal for a while. Of course, I had cleaned/lubed then changed the calipers first before I figured it out. :(

Couldn't see anything wrong with the hose.

The brake line failure mode is fairly well known in very old cars, specifically 70s-vintage European cars with original brake lines. I'm not sure if American cars of that vintage have similar problems.

BuWHAAAA???? Plastic piston in the caliper? Doesn't the heat do Very Bad Things to the plastic?

-soD

Better look for signs of swelling in the master cylinder by checking the condition of the cap too.

Almost everything that isn't a heavy duty truck has plastic pistons.

Hah? :confused:

Look at the seal for the brake fluid filler cap to see if it shows signs of swelling or gumminess. If so, you master cylinder may be in the same clogged condition as your flex hose.

Nice work. Thanks for sharing the process and discovery. Instructive.

Can't believe it's the first time it's happened to you. My 84 s blazer had both front brakes smoking and tires leaking cause of brake hoses and only after a couple miles.

I've cleaned pistons/cylinders on dirt bikes, but just toss & replace car stuff. Might have to tear the Impala's pistons apart.