I did 17 years testing and developing brakes for Ferodo (you guys might know it as Federal Mogul) and I’m bewildered by some of the comments in this thread.
“All brakes squeal” - No they don’t. They can squeal under certain conditions but it certainly isn’t normal.
“Most pads are ceramic” - no they aren’t. Most pads are made from steel fibre, friction modifiers like silica (abrasive) or carbon (lubricant) some of which are active at different temperatures and they are all bonded together in an oil based resin which is what stinks if you get them hot (you can sometimes smell it on trucks if you follow them down hills).
"The discs/pads are glazed”. It depends what is meant by this. Discs and pads will only work as designed if they are very clean and very shiny. The same applies to a freight train loco. If the wheels and rails are very clean and shiny, the loco can get thousands of tons moving even up grade and even in the wet BUT, put humble leaves on the line and it won’t move an inch. The secret is perfectly smooth and clean surfaces and how hard you push them together and on that loco, it has the footprint the size of a dime which imposes phenomenal pressure. In the case of brake pads, the same applies. Huge hydraulic pressure (you can easily apply 1500 psi in the hydraulic system) working on a 1.5-2 inch piston. So the comment about being glazed? I’ll allow that to be true if it refers to them being contaminated and in that case, the best way to clean them is to get them hot.
So what about these squealing CX-5s then? Well first of all you need to understand brake squeal. When a pad grips a disc, if you look on a micro scale what is happening, there is a moment in time when a pad welds itself to the disc (caused by the abrasive content but NOT a rough surface) and a moment when it breaks free (see, there’s an example of the word break and not brake!!!). This stick/slip process is perfectly normal and the way all pad/disc relationships work. Apply it to a more practical example. Wet your finger and run it round an empty wine glass. When the finger dries enough, it will start to stick/slip and the resultant impact at the time of the stick/slips taking place, all joint together and give a constant joined up noise - many little taps of the glass give one perceivable ring - its the same on a disc brake. Here’s the difference though. It only happens when the pad and disc are in contact - not in the “off brake” condition. Also, when the pads come under pressure, it has the effect of dampening the vibration - the same would happen if you pressed heavily on the wine glass. How is this all dealt with in a brake? Well they have gone to an awful lot of trouble to stop it. The pad itself has a layer of dampening material stuck to it and then there are a one or a number of shims - all of which have been specially designed to absorb vibration. The problem comes when something stops them from doing their job and that something is usually nothing more than dirt sticking them all together. After a number of miles, depending on duty levels and environmental conditions, the pads become very dirty. Inside that wheel is one of the most vile inhospitable environments on earth with heat, cold and rain lashing round them and they are fed by a constant supply of road dirt and wear debris from the pads. The result is those dampeners get stuck solid and the pads often stay in slight contact with the disc - a beautiful bell if ever there was one and much better at ringing than a wine glass. So when the dealer takes the car in the garage, the mechanic looks in the brake calliper and sees just what he is expecting to see - a dirty calliper. with no apparent faults. Sure, he gets his SnapOn screwdriver and forces the calliper open and a quick dab of copper grease and then declares no fault to the customer. Well here’s the thing. It will never be any better unless he pulls it apart and cleans the pads, shims and the abutments which on mazdas are fitted with very high quality stainless pressure springs at the abutments. I wash my car at least once a week and use a pressure washer every time. When I wash the wheels I also pressure wash the callipers through the wheels and I never get brake squeal. I accept this is not always possible for owners and in some cases they never get washed but you can’t blame the car or the friction material when they squeal. You could have a car that never gets washed and never squeals because they see enough heavy duty work to self clean and never allow dirt to build between the layers of shims. These will wear out quicker because brake wear rises exponentially with temperature. The squeal itself does not harm, it is more of an annoyance so if the conditions are right to generate noise you could either have them regularly stripped and cleaned or just ignore it.
To finalise, a couple of points. Never, ever use copper or aluminium grease to lubricate brake parts. It is clay based and after a very short time, the lubricant content disappears leaving the clay base to stick all the parts together. Instead, just normal high melting point bearing grease will last much longer and is perfectly capable of dealing with all but very spirited driving or competitions. The same goes for that hub where the the wheel mounts! There is a special grease called Ceratec which is designed for brakes. Nothing beats it and you should be able to get it or an equivalent ceramic based grease over there. It looks just like normal bearing grease.
Finally, if anyone says “the pads are hard” tell them of course they are hard, they are bloody brake pad - made from steel fibre and resin!!!
