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Front brake squealing

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Athame57:

--- Quote from: McCabe-Thiele (Ted) on April 25, 2026, 06:56:20 PM ---A chamfer on the leading edge of the pad can help.

--- End quote ---
That's what I do besides the copper grease treatment. I always called it a bevel myself.  8)

Oddjob:
Fair play to you Mick for sticking with it. Sometimes things can just elude you until you finally have an epiphany and it all slots into place.

Let me see if I can cause that. The adjusting screw is threaded into the slider and locked into position by the locknut. So the spring can only force it back as far as the screw allows. IF it wasn’t threaded then you’d be correct and it would indeed cause some brake pad drag.

The piston pad is self adjusting, in that it will allow the pad to slide out further as the pad wears, evidenced by the fact the piston needs to be pushed back into the housing when you fit new pads which will of course be so much thicker they’ll cause severe drag or even bind the wheel solid. The most gap between the piston pad and the disc is only ever a few thou if it’s working correctly. Hence minimal travel on the brake lever. You apply the lever, that causes the pad to travel out, and yes you are 100% correct, the piston seal distorts as it does so. When the piston pad touches the disc then as you apply more pressure the arm is forced to move and the back pad starts to touch. If it’s out of adjustment then you find the lever has to travel further to compensate. When you release the pressure, the spring on the adjusting screw forces the arm away from the disc, causing the rear pad to disengage. It will go back as far as the screw allows it to and no further. By this time the piston pad is also being retracted by the force of the seal distortion, it’s a really small movement and is just enough to allow the pad to clear the disc surface. You may still hear some pad drag on the surface however as even a modern caliper does that sometimes, I can hear my 4 pot calipers allowing it as a sort of hiss as the pad slides across the drillings on the disc.


I hope that helps you.

Mikep328:
FWIW, I mentioned bedding-in as being important for braking power/feel and MAYBE for squealing.  I thought I should explain that the procedure I found so successful is NOT the typical recommendation that you hear for a new bike/new pads which is typically to perform gentle stops for the first 100-200 miles.  I tried to find the post where another member posted a break in procedure which I used but couldn't find it.  So below is a link to a site that has the same procedure.  https://www.denniskirk.com/blog/2019/03/06/how-to-break-in-motorcycle-brakes/

K2-K6:

--- Quote from: Mikep328 on April 28, 2026, 06:44:58 AM ---FWIW, I mentioned bedding-in as being important for braking power/feel and MAYBE for squealing.  I thought I should explain that the procedure I found so successful is NOT the typical recommendation that you hear for a new bike/new pads which is typically to perform gentle stops for the first 100-200 miles.  I tried to find the post where another member posted a break in procedure which I used but couldn't find it.  So below is a link to a site that has the same procedure.  https://www.denniskirk.com/blog/2019/03/06/how-to-break-in-motorcycle-brakes/

--- End quote ---

Agree with bedding the pads.

Some time ago and working with pads in more extreme use, speaking to AP, Ferodo, Mintex etc about this as it was routine in competition systems where glazing is more prevalent. Broadly, the initial phase is to get the two surfaces to match through gentle wear, then to condition the pads and rotor surface by higher heat input that both burns out any unwanted production "contamination" and eventually transfers some of the pad material to the disc surface.
Often claimed that Sintered type didn't need this, but experience over different materials showed benefit nonetheless.

For road application, in the order of 50 miles light use will complete the first step of physically matching surfaces without problem. Then to drive them up into higher temperature range to complete the process. Successive hard stops and or dragging the brake to build heat prior to some very high energy braking will work well. You'll feel the change coming into the system as you do this.

K2-K6:
The seal and it's operation.

A single piston caliper must have seal arrangement to cope with clearance for two pads. How that's distributed here is what seems misunderstood. 

With a sliding pin caliper, the body floats in doing this, and freely depending on how the pins are lubricated.

These Honda type are restricted float (by setting that adjustment screw) and need to be moved in tracking/accommodating wear in that static pad.

If, for example, you set the static pad clearance at 5 thou, and the seal rollback had 10 thou capability, then you'd see 5 thou each side when releasing the brake.  Then as the static clearance rises during use, the piston has to first pull the static pad into contact before braking occurs. When its released, that increaese in static clearance will be "consumed" by the static pad and forced by the spring.
Once 10 thou static clearance is reached thats all of the seal capability now taken by that location. Wear from then onwards will always leave the hydraulic pad dragging excessively on the rotor surface, ultimately to glaze that pad.

The seal cross section and seal groove taper are designed for each application, a four piston "rigid" caliper will use different dimensions to facilitate that type, bringing down rollback specification is used to get more immediate clamping when applied and fine with dead straight rotor and rigid caliper mounting.

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