When it acts up so seldom it is going to be almost impossible for a mechanic to diagnose it. No different than a doctor diagnosing you when you feel fine. All we can do is go on your observations.
One clue to a restricted flex hose is the brake pedal will be higher and harder than normal. You'll be able to force brake fluid through it by pushing on the brake pedal but the fluid won't want to return and let the caliper release.
A clue to a sticking caliper is under light pedal application the piston won't want to slide out of the caliper to apply that brake so the car will veer the other way, and under hard braking it will stop straight, then pull in the direction of the sticking caliper when you release the brake pedal. One thing to understand related to that pulling is almost all front-wheel-drive cars use what's called the "split-diagonal" hydraulic system. All cars have two hydraulic circuits; one for some stopping power in case the other one pops a leak. Since front-wheel-drive cars have such a high percentage of their weight on the front, you always want to have at least one front brake working, so one front brake and the opposite rear one are on the same hydraulic circuit instead of the two fronts together and the two rears together as on older cars and trucks. That could cause a horrendous brake pull if one hydraulic system had a leak. Alignment geometry has been modified on those cars to offset any brake pull caused by a failure in one system. Chryslers in particular have completely done away with the resulting brake pull. On other cars all you may see is a little wobble in the steering wheel when you hit the brakes when one circuit isn't working, but that's about it.
Didn't mean to get too far off topic but those are a few of the things we look for on initial test drives. Another valid test is to jack the front end off the ground, run the car in gear, lightly apply the brakes, release 'em, then see which wheel doesn't want to turn. You may even find you can barely turn one wheel by hand. You should be able to turn each one with one hand. Another simple test is to stop on a slight incline, shift to neutral, release the brake pedal, then see if the car creeps downhill on its own. If it doesn't, you have something to work with. When you get it to stick, THAT'S when there's something to diagnose.
Once it's sticking the diagnosis involves opening up the hydraulic system to the suspect brake to see if and where the brake fluid is trapped under pressure. I like to park on that incline and leave the car in neutral, then place a block of wood about six inches downhill of one of the tires. That's because I'd look silly running after the car if the brake releases! The easiest place to start is usually at the master cylinder. Use a line wrench, (also called a flare nut wrench), to loosen one of the soft metal nuts holding a steel line to the master cylinder. If nothing happens, tighten it and loosen the other one. If you see a tiny spurt of brake fluid and the car starts rolling downhill, you have a serious cause for concern. That means the fluid was trapped by an expanded rubber seal inside the master cylinder. That's due to the fluid being contaminated with a petroleum product, and it doesn't take much. That repair involves replacing everything in the hydraulic system with rubber parts, and in some cases that costs more than a ten-year-old car is worth.
Now, the good news, if loosening those steel lines doesn't let the brake release, you have a less expensive and more common problem. The next step involves crawling under the car and opening the bleeder screw on the suspect caliper. If that releases the trapped brake fluid it's almost certain to be caused by a restricted rubber brake hose. That is a real common problem on Chrysler products but it has a one-minute fix that doesn't cost anything. Your hose is of a different design but the crimp connectors on the ends can rust and expand which can constrict the hose. Opening the bleeder screw releases that trapped fluid which releases the brake.
If opening the bleeder screw still doesn't let the brake release, it is definitely a sticking caliper. That is usually an issue with age, not mileage. Rebuilt calipers are pretty cheap and they should always be replaced in pairs to maintain even braking. If it comes to that there is a big list of things I'll share that professionals do and avoid to prevent causing noises and vibrations. A good brake job is way more than just slapping in new brake pads.
Sunday, September 23rd, 2012 AT 4:35 AM