Brake squeal noise

Rotors rusting when sitting idle in humidity can cause brake noise which goes away. More than likely the rear brakes are dirty though. Probably need to be cleaned and adjusted.

Try driving up to 35 MPH but not exceeding 40 MPH, then shift to N and brake to a complete stop. Do this a couple of times and that should clean up the rotors.

When looking at pads, check the inboard one also. Visible through narrow slot underneath. Not easy to see unless the car is on a rack. If the glide pins get dry and or rusty, the pads can stick and wear the inboard pads prematurely which will cause noise. It doesn't happen a lot, but can happen.

 

Shift to N below 40 and brake to 0 - Friction brakes normally don't kick in until 7 mph unless you are in N, then full friction brake comes into play. Don't do this over 40 as you can overspeed the MG's and damage them.

Doesn't matter if you brake slowly or quickly, just do it a couple of times and see if it makes a difference. I do this if the Prius has set a few days with the humidity high. Like after a good rain or high humidity. It is real obvious when the rotors are rusted as the brakes will kind of grab when stopping normally when you get down to 7 mph if you are holding steady pressure. They usually only do that a couple of times until the rotors get dried off and cleaned up.

I still think the squeal is dirty or rusty brakes probably the rear drums needs to be cleaned and adjusted. Usually the Prius front brakes last a long time unless the glide pins get dry and rusted as I mentioned earlier.

I do mention that because I have personal experience with that. The Prius we have came from Florida. It was rental car. Brakes were real noisy when we bought it. At 53K I had the brakes inspected. I found the inboard pads were wore down to below minimum, but outboard pads had plenty of meat. Also both rotors had rust imbedded on them and were too rusty to turn due to the small amount of material that can be removed before minimum comes up. I elected to replace rotors, install new pads, clean and lube the glide pins as well as clean and adjust rear brakes. Since then the brakes have been very quiet and work properly. My situation was not normal, but is not unheard of also. Several post's here on PC about the glide pins and inboard pads wearing prematurely.

Hope this helps.

 

One other thought, if you have a dial or digital indicator and a mag base, pull the front wheels and rotate them with the indicator on the rotor. Check for runout when rotating the hub assembly. If the rotors are warped, that might explain the sound. Not sure what the max runout is, but there should not be a lot of excessive movement of the indicator when you are rotating the hub assembly. If there is, I would suspect a warped rotor or a bad wheel bearing. If you don't see excessive runout, then inspect the rear brakes.

I am still betting you will find some rust in there when you pull the drums. It is a common problem that happens all the time with drum brakes. Intermittent squeaks that come and go. Cleaning and adjusting them usually quiets them down.

 

Pads need to be able to freely move on the slides in the caliper. First, clean the pad rails. If they still make noises or has no slack, file half a mm of the pad rail, the tongues that guide the pad in the caliper, away. The whine comes from the pads not retracting from the rotor on break release.


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Had the same as many others. No copper slip or any other grease on those rails please. The dust starts sticking to the grease until pads do not move anymore.


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