Dandy. The first thing to consider is if you got any type of grease on the linings or drums and rotors. That won't cause a problem if it's washed off right away with brake parts cleaner, but if it goes through one warm-up cycle, the grease will soak into the linings and rotors and drums. Cast iron is porous, and once the grease soaks in, it's never coming out. Brake system specialists even wash their hands with soap and water before touching brake parts to prevent getting fingerprint grease on brake parts. If these parts are contaminated, the only remedy is to replace them again.
The next thing is if high-temperature brake grease was used in all the right places. Proper procedure is to drag a flat file across the fingers of the calipers that the outer pads mount to, and across the surface of the pistons where they contact the inner pads. Those surfaces don't have to be shined up. All you're after is to insure there are no high spots of dirt, rust, or old silencer material that would prevent the pads from sitting squarely against the caliper. The pads are going to vibrate. We can't stop that, but we can minimize the squeal that results. Being mounted solidly to the caliper makes it harder for a pad to vibrate, but the next step is those caliper surfaces that touch the backing plates of the pads must be lubricated with that high-temperature brake grease. "Rusty Lube" is one trade name I'm familiar with, but there are many others. All of the products contain molybdenum disulphide. The grease allows the pads to vibrate freely without transmitting the noise to the calipers where it would be amplified. This is absolutely not the place to use any type of axle grease, wheel bearing grease, or any other petroleum-based lubricant. Those will travel and could contaminate the linings, and they will burn off from the normal brake system temperatures.
The caliper mounts must also be cleaned and lubricated with that brake grease. Some calipers sit on long flat mounting surfaces. Those must have the file treatment, then the grease. Most calipers bolt on with some variation of chrome-plated bolts or pins. If there is any pitting, rust, or lifted chrome on those bolts, they must be replaced. If they're bent, they also must be replaced. Rust pits and being bent will cause the caliper to stick when it needs to slide a little to self-adjust. If there are rubber inserts the bolts go through and those are worn or damaged, a vibrating caliper can touch the bolts and transmit that noise to the steering knuckle or spindle where it will be amplified.
Some pads come with thin metal plates, (shims) that are stuck or clipped to the pads' backing plates to reduce noise transfer. I don't have an opinion on how well they work, but if they include a tube of glue with the new pads, throw that away! Some pads have thick paper shims applied during manufacture. On old pads you'll find those wadded up inside the pistons. That proves the linings are moving around. The brake grease allows the pads to move freely and not transmit noise. The glue is intended to hold the pads from vibrating. Nice try, but it's never going to work.
There is one squealing problem that only Ford had that goes back to the 1970s and 80s. I suspect they have fixed that design problem by now, but it was so common that bares mentioning. If you look at the rear shoes where the "nails" go through that hold them to the backing plates, those holes are not in the center of the shoes. They are down near the bottom. That leaves the top two thirds of the shoe frames free to vibrate. When you replace rear shoes, you'll see six raised spots on the backing plates, three for each shoe. Those "lands" must also have a light film of brake grease. That will stop some of the vibration from transmitting to the backing plates and being amplified for a little while.
Keep in mind that brake linings are no longer made of asbestos which was very quiet. The noise became a problem when other materials were used so a little noise can't be avoided. One thing that has a real big effect on squealing is "preparing" the pads. That involves cutting a 45 degree bevel on the leading edges of the linings. Some people do that with a bench grinder, but a few passes with the flat file will do the job. This removes the "fingernails-on-the-blackboard" screech. Don't get carried away. If you can stop that source of squealing during the break-in period, they won't squeal later either. If you make the beveled area too large, you'll lose the squeegee action that removes water when you drive through a deep puddle. That water will cause one form of brake fade that won't last long, but it still must be avoided. Some cars, GMs in particular, come with pads that are so heavily-beveled to reduce noise that they take a long time to recover after driving through deep water.
Also be aware that when rotors are machined, they have grooves like a phonograph record. The deepest part of the grooves do not touch the brake linings so your stopping power is greatly reduced for the first 100 or so miles. By that time the linings have worn down very quickly to match those grooves. The industry-accepted standard procedure is for the mechanic to perform a half dozen pretty hard stops from highway speed, with a minute or two in between each stop for the parts to cool down. That will accelerate the wearing-in of the linings. I had one car where the owner was in too big a hurry for me to do a proper test-drive. After driving about five miles through city stop-and-go traffic, she developed another type of brake fade. That was due to severe overheating of the pads because they weren't yet making 100 percent contact, the braking power was reduced, and she didn't realize how much harder she was pushing on the brake pedal to stop the car, (minivan, in this case). She parked the van and by the time the tow truck got there an hour later, the parts had cooled down and the brakes were fine. All that misery because a proper test-drive / break-in procedure wasn't performed. This also should have been avoided by the service adviser explaining the break-in procedure that she was going to have to do. Many shops hang informational tags on rear-view mirrors as part of their brake jobs that cover the break-in period.
Along with that overheating, that will cause the binders in the linings to melt. When that cools and hardens, it forms what we call "glaze"; a shiny, hard surface that doesn't have the same friction characteristics we need. It's actually too sticky and can really set up a squealing problem. Typically when that happens on freshly-machined used rotors, the grooves are still there and they will act like a file and cut that glazed material off. This becomes a problem more often when older, well-worn linings become overheated, like when dragging a heavy trailer. The grooves have worn smooth on the rotors so there's nothing there to cut the glazed material off. Every mechanic has his favorite trick to solve that. Mine is to simply take a light pass on the rotors with the brake lathe. That cuts the impacted resins from the rotors and the grooves will do the rest on the pads. Along with that, almost all manufacturers require a very specific "surface finish" when rotors are machined. Once machined, that involves using a rotating abrasive disc to cut down those grooves and leave a "non-directional" finish.
At this point something should have stood out as a good suspect. I can offer two more tidbits of value, but I'm pretty sure they don't apply to your car. One is that a lot of pads have wear indicators riveted to them or attached during the brake job. I have seen people switch a left and right-side pad and end up with the "squeakers" in the wrong orientation. If you can get the pads in easily that way, it likely won't cause a problem, but most pads wear unevenly, faster toward the rear of the pads, and if the squeakers are back there, they might start squeaking too early. One clue is those wear indicators typically cause a light, high-pitched squeal when you're NOT applying the brakes, and they get quiet when you apply the brakes. If the pads are in backward, the wear indicators will squeal when you apply the brakes. It's simply a matter of the leading edges, (rear edges) of the pads pulling in closer to the rotors during braking while the trailing edges push out, away from the rotors. This installation error usually doesn't cause any other problem.
The last one was I was asked to find the problem on an older Dodge Caravan an inexperienced mechanic had just done a brake job on. He noticed a grinding noise on a rear wheel before he ever went on the test-drive. Turns out he had the parking brake strut bar upside-down on the left wheel. It has a small curved area to avoid hitting the hub of the brake drum. By being upside-down, it rubbed on the drum. He spent a half hour trying to find that, and I didn't see it right away either. The marks in the rust on the drum provided the clue.
One more thing I just remembered was on the rear drums of a smaller front-wheel-drive car, (don't remember the model), there was an irritating high-pitched squeal from the left rear all the time. The drum was real small, and the parking brake lever sat so close to it, the "knot" on the end of the parking brake cable was able to rub on it. Can't remember if the cable wasn't seated fully or if we had to do something else. Never saw that on any other car before or since, and I don't know what caused it on that one.
Saturday, September 10th, 2016 AT 11:58 PM
