What makes a brake pad squeal in stop & go traffic?

Joined
Jan 2, 2004
Messages
10,902
Location
California
Vehicle: 2005 Toyota Sienna, rear drum/front disc, no VSC(Toyota/Denso/Advics implementation of ESP).

I’ve noticed a squeal from the front brakes when the van is in stop & go traffic - this happened in the line waiting to get into Yosemite two weeks ago. Else, the van stops fine and the noise goes away and stays gone. Yesterday, my parents drove the van and the noise was back. My dad chalked it up as weird but normal braking behavior, my mom was panicking and called me in a tizzy while I was out on the river with friends for the day.

The brake pads installed are Toyota “warranty” pads, made by Advics with a FF friction level. I didn’t note the formulation number. 8mm left, so plenty of life. I took the front brakes apart, sanded the pads on a flat piece of marble with 150 grit sandpaper. Installed new aftermarket abutment clips, put a thin smear of Permatex moly silicone gray brake lube on the backs of the clips, as well as the “ears” of the calipers where they touch the outboard pad and on the piston. Noticed the passenger outboard shim sandwich fell off, so I bent the tangs to secure them back on, with a few dabs of lube between the shims and backing plate. Took the van out on a drive, brakes feel fine - I will note a local machine shop turned the rotors when the pads were replaced and there was a bit more runout than I would have liked.

Now, while Japanese cars use NAO “ceramic” friction that works on the cohesive friction principle, shouldn’t there be a microscopic(as in microns) layer of friction on the rotor at all times that’s constantly renewed when the brakes are applied? What else would cause this low-speed brake squeal?
 
It is possible that the rotors are glazed. Rotors can get glazed when they are cooled down rapidly, when very hot. For example, going through a car wash right after driving at highway speeds and/or hard braking. The only way to get rid of the squeal is to turn or replace the rotors.

Ask me how I know.
 
It is possible that the rotors are glazed. Rotors can get glazed when they are cooled down rapidly, when very hot. For example, going through a car wash right after driving at highway speeds and/or hard braking. The only way to get rid of the squeal is to turn or replace the rotors.

Ask me how I know.
Well, the Advics rotors I installed with a set of first generation of Toyota “service” pads were turned when I installed these pads. If there’s still squeal, I’m getting rotors.

My mom wanted me to parts cannon a set of pads on it. Meh.
 
Clean the hardware lube it up, and that probably will help

If your Sienna is anything like my GS350, this is the cause.
Yep, grabbed a Carlson disc brake hardware kit and installed that too. The pins are fine - brakes are wearing nice and evenly. Put some Permatex silicone lube on the underside of the abutment clips as a guard against rust jacking too.
 
Well, the Advics rotors I installed with a set of first generation of Toyota “service” pads were turned when I installed these pads. If there’s still squeal, I’m getting rotors.

My mom wanted me to parts cannon a set of pads on it. Meh.

Always replace the rotors along with the pads
 
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