This goes back to my comment about being able to pry the pistons in with a screwdriver before unbolting the caliper. Did you find a ring of mud on the piston? How did the chrome finish look after you cleaned it? If there were any rust pits, the piston must be replaced. Sanding the lifted chrome is not the proper fix for that.
I worked for seven years in the '80s at a Sears Auto Center where we mainly did steering, suspension, and brake work. On a typical day I would do two or three brake jobs and we rebuilt calipers and wheel cylinders on about nine out of ten cars. Our "All-In-One" kits came with all the seals and dust boots. In all of those hundreds of brake jobs we never obsessed about how hard the caliper moved sideways by hand. Our main concern was keeping every little hint of grease or any petroleum product out of any place it contacted brake fluid. We even worried about fingerprint grease. When reinstalling the pistons we needed to be able to work them in by hand until they were fully seated. If we couldn't, we did something wrong. In those days a replacement piston cost $20.00 and a professionally rebuilt caliper from the auto parts store cost around $90.00 so rebuilding them ourselves in-house made economic sense.
By the time I got to the dealership all through the '90s, rebuilding calipers was a lost art and few other people even knew how to do it. I rebuilt only three in the ten years I was there because calipers were not immediately available but the kits were.
Rebuilt calipers today are so inexpensive that it doesn't make sense to rebuild them yourself. The kits cost almost as much and you will never get the groove for the dust boot as clean as they do at the factory. If you have to replace the piston, you're guaranteed of having more money involved than just buying a rebuilt caliper.
Regardless whether you buy or rebuild a caliper, it still sounds like you're worried about a non-existent problem. If you apply the brake pedal, release it, then you can not turn the rotor by hand, you have a sticking piston. If you believe it's the caliper sticking on the metal tubes, you can prove it by prying the piston back in with a screwdriver through the large hole in the casting in the middle of the caliper. You can catch the piston or the pad to pry on. Even if you were able to move the piston, then still not be able to turn the rotor, I still would not concern myself with that because the forces acting on the caliper while driving are a whole lot higher than what you can do by hand. I mentioned previously the Ford truck calipers that were mounted with steel wedges with spring steel inserts. You needed a hammer, (that is not an exaggeration), to move those calipers and they just got worse once a little dirt got in there. That was considered normal and it was how they were designed. If you can slide your calipers by hand when you install them, put it together and go out and drive it to verify everything is working properly. No professional ever waited a half hour, then checked to see if they would still slide. If we did, we might find the same thing you did and we wouldn't get any work done.
If you still have a problem with a dragging caliper, there's three things to consider long before looking at how hard they slide. The first is they came with phenolic pistons. Chrysler had a big problem with those in the late '70s but not much after that. They would grow and stick. The only cure was to replace both of them with chromed steel pistons. Most manufacturers now use phenolic pistons to save weight and they rarely have a problem.
The second thing to consider is a restricted hose. That has been a fairly common but elusive problem on other models that have a metal bracket crimped around the middle of the hose. Rust builds up inside that crimp and constricts the hose. Pedal pressure will force fluid through to the caliper, but the square-cut seal deforms, then straightens out to retract the piston a little, and it's not strong enough to push fluid back through that restriction. You can identify that by stopping on a slight incline, in neutral, put a wheel block a few inches downhill, then crack open a steel line at the master cylinder. If the brake releases, or if multiple brakes are staying applied, you have contaminated brake fluid, or the power booster push rod is too long, (if work related to that was just done). If the brake doesn't release, crack open the bleeder screw on the stuck caliper. Now if it releases, suspect the hose. Your hoses don't use that metal bracket but there have still been instances where they trap fluid.
As long as the piston is releasing properly, a caliper sticking on its mount can't cause that brake to drag. There is way too much play in the wheel bearings to maintain that drag. Either the rotor is simply going to move away from the outer pad or it's going to be bounced around and will pound against the outer pad forcing the caliper to move. Under normal conditions the piston and caliper only release a few thousandths of an inch. That's the equivalent to the thickness of a sheet of paper.
The third thing that has me the most concerned is the type of cleaning chemical you washed the calipers in. Many of them are petroleum-based and not acceptable for cleaning any brake components that contact brake fluid. Some of them use a chemical to dilute fuel oil. The only thing that should ever be used is brake parts cleaner which is most commonly found in spray cans. It is even better than carburetor cleaner in that it takes longer to evaporate giving you a longer working time to scrub parts. I don't recommend carburetor cleaner either due to the risk of it also being petroleum-based. It is meant to evaporate quickly as it goes into the engine, and that defeats its purpose of hanging around long enough to give you time to clean parts. If the cleaner you used has any hint of petroleum in it, including from parts the previous people washed, you have contaminated the entire brake system and repairs will be very expensive. Calipers are made from cast iron which is porous and will absorb those chemicals. Those chemicals will continue to leach back out and recontaminate any new fluid and parts. The fix for that is to replace every part that has rubber that contacts the fluid, and flush and dry all of the steel lines. That includes wheel cylinders, calipers, combination valve, master cylinder, and rubber hoses. If the vehicle has anti-lock brakes, the hydraulic controller must also be replaced since it has rubber 0-rings and lip seals.
Every year I did a demonstration for my students to show the importance of keeping brake parts clean. I had two small beakers, each with an inch of brake fluid, and in each I dropped a lip seal from a wheel cylinder rebuild kit. In one I also placed one drop of power steering fluid. One week later the seal in the contaminated fluid had grown by over 1/8" in diameter and was soft and mushy. The rubber might still seal but the square-cut seal in the caliper is meant to stick to the piston as it is applied, and it deforms slightly because of that. When pressure is released, the seal straightens out and pulls the piston back with it. Being soft and mushy, it will not pull the piston back. In the master cylinder the lip seals will expand and grow past the fluid return ports blocking them off just as if you were holding the brake pedal down a little. That will lead to both front brakes dragging. On split-diagonal systems found on most front-wheel-drive cars, one brake will always be affected first, then the second one days later as the contamination spreads. Rear drum brakes will not drag because the shoe return springs pull the shoes back as the brake pedal is released.
I'm really nervous about what was in the cleaning chemical you used. That is a lot more significant than not being able to slide the calipers on their mounts. I shouldn't even say this, but you might want to replace both calipers and both rubber hoses, run new brake fluid through the steel lines before the new hoses are connected, until clear new fluid comes out, and hope no contamination has spread beyond that. Replacing just a few rubber parts is not the way we teach doing conscientious work but given the cost of replacing everything, and the fact the work was just done recently, you might very well get lucky and avoid the bigger expense.
Friday, June 22nd, 2012 AT 6:45 PM