Question on squeaking disc brakes

JP

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Make
Chevy
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Equinox
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2015
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6 cyl.
Right, so where exactly does the squeak from disc brakes occur? Assume new pads and rotors i.e. not a wear indicator. Does the sound come from the brake pad rubbing on the rotor or from the back of the brake pad(s) against the caliper piston or caliper?
 

wolfsmane

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Back of brake pads.
 

gfbidd

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some times you need to chamfer the leading and trailing edges
 

JP

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So...the back of the brake pad only can move a what...couple mm or so, then it reaches an endpoint and cannot move any more. Why would it continue to squeak if it's more than a brief squeak? (Does that question make sense?)
Nickb, the video is unavailable. bummer.
 

billr

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It isn't squeaking from the in-out motion. It is squeaking because it is fluttering between the rotor surface and the caliper piston/housing. Yes, the pads are not clamped solid against the rotor. They are just tight enough to give the braking friction desired. The combination of friction force on the pad face and the resisting force of the steel pad base are not exactly in a straight line. There is an offset of about the thickness of the pad. This produces a left-right torque on the pad, which changes the pad pressure and point of application slightly... which changes that torque... which changes the pad pressure again... on and on. At some point, all these physical forces and slight pad movements hit a resonant frequency. The pads, caliper, and rotor are all rather robust and stiff pieces, so the resonant frequency is bound to be high.

The sound itself may well be from the rotor vibrating, it is a big "sound board", but I am pretty sure the mechanical forces that cause the rotor to vibrate are as I attempted to describe above
 

JP

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It isn't squeaking from the in-out motion. It is squeaking because it is fluttering between the rotor surface and the caliper piston/housing. Yes, the pads are not clamped solid against the rotor. They are just tight enough to give the braking friction desired. The combination of friction force on the pad face and the resisting force of the steel pad base are not exactly in a straight line. There is an offset of about the thickness of the pad. This produces a left-right torque on the pad, which changes the pad pressure and point of application slightly... which changes that torque... which changes the pad pressure again... on and on. At some point, all these physical forces and slight pad movements hit a resonant frequency. The pads, caliper, and rotor are all rather robust and stiff pieces, so the resonant frequency is bound to be high.

The sound itself may well be from the rotor vibrating, it is a big "sound board", but I am pretty sure the mechanical forces that cause the rotor to vibrate are as I attempted to describe above
Gotcha. The resonance makes sense.

I've sucessfully used...don't remember the name of the product...some orange glue-like goop to stick the pad to the caliper on one side and to the piston on the other. I'm due for front struts so maybe I'll give that a go.
 

billr

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Yep, goop is a common fix for the problem; along with a wide variety of soft shims or spring clips. Anything that will change the stiffness-to-springiness relation of that circus and shift the resonance frequency away from an annoying point. I expect all disk brakes can vibrate like that to some extent, it is just a matter of at what loads and frequency. I wonder if "sliding caliper" disks are more prone to annoying squeak than fixed? Harder metallic or ceramic pads (and shoes, with drums) have long been know to be more squeak-prone.
 

nickb2

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(Does that question make sense?)
yes, it makes sense.

When I do a brake job, spew a whole bunch of this permatex shyte on the piston side, slide are always synthetic grease, wurth style.




 
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