Mazda Forum - Mazda Enthusiast Forums - Strange Noise on my CX-9

I own a 2011 Mazda CX9 with 106,000 miles. I do all my own automotive work and have for the past 55 years. I rebuild engines, transmissions and do all the electrical work required. I NEVER have taken a car to a garage for service. Back in July, started hearing a sound that was like a tire with a flat spot. Sometimes you could slightly feel it sometime you couldn’t. My tires were close to being in need of replacing and so I put new tires on the vehicle. Didn’t make a difference. Car drives perfectly but is making this rapid dud – dud – dud sound with the noise being the worst at about 65mph. The sound was worse when the car was cold and would often go away after about 10 miles. I started checking things. I found nothing.

Finally, one day on my way home it started making the noise and instead of slowing down I took the car to 90 mph to see if the noise got worst or better. It got worse and when I slowed down to turn down my road the brakes were pulsing.

I pulled into my driveway and got out now thinking that something strange was happening with the brakes. I put my finger through the aluminum rims on the Driver’s side front placing it on the hub to feel for heat – warm only. I went to the Passenger side and did the same thing and promptly burned my finger! I retrieved my point and measure IR thermometer and took a temp on both sides; Driver side – 150 F, Passenger side – 330 F. I had found my problem.

Turns out that one of the dual pistons in the caliper was sticking. It was fine when I replaced the brakes a few months before. Time for an autopsy. I used a hydraulic system to force the stuck piston out of the caliper. I found that the chrome plating on the pistons was failing and flaking off in areas. This loose plating was freezing the piston. The start of this flaking was also visible on the piston that was still functioning normally. I replace the entire caliper and things seem to be back to normal.

In the past couple of weeks, I started hearing the same sound again. It was faint but defiantly there. Time for the finger test. This time it was the Driver’s side that was beginning to get hot. Yesterday I replaced the Driver’s side caliper and the car is back to normal.

Finding the source of this noise has driven me crazy! It wasn’t consistent and would disappear for weeks. The Mazda drove perfectly; never pulled and no smell of hot brakes.

The brakes on this Mazda are of Ford origin. They have FoMoCo cast all over them. I have found they are the exact same calipers that are used on the Ford Edge (2010 – 2013?) These are the first calipers I have ever had to replace on any of the many vehicles I have owned. Sometimes a piston might start dragging on a caliper requiring that I remove the piston and clean it up. Removing any varnish or surface rust that was developing on the piston would fix the problem. Once properly cleaned and treated to prevent further rust the caliper could be reassembled and it would work perfectly. Obviously, the chrome plating on these pistons was not done properly. Since both sides of my vehicle had the plating fail, I would watch my brakes closely if you own a set of these calipers.