Front brake squealing

[TrickyMicky]

Surely once the initial clearance has been achieved, unless there is a problem, or pads have been renewed, it should not need adjusting. When releasing the brake lever, the seal on the piston reverts back to its normal shape giving the required distance betqeen pad and disc.

[Oddjob]

The gap increases as the static pad wears Mick, so it must be checked every few thousand miles to keep it at max efficiency.

[K2-K6]

Surely once the initial clearance has been achieved, unless there is a problem, or pads have been renewed, it should not need adjusting. When releasing the brake lever, the seal on the piston reverts back to its normal shape giving the required distance betqeen pad and disc.

As Ken notes, they only do half of the adjustment and need regular attention.

The "fixed" pad, once set to clearance by adjustment of the screw, then returns to that same reference by the little spring pressure on that bolt .... that's regardless of how much material is worn away from braking. Effectively you've got to chase that pad's wear with the adjustment.

The hydraulic piston and it's seal has to accommodate BOTH sides in it's return travel to work correctly (same as a single sided one piston caliper does) else the back pad can't get enough clearance when brake is released.

BUT, once the fixed pad gets too much clearance the spring return will then cause the hydraulic piston to drag as it let's the caliper swing too far on release. Also the lever travel gets longer too on brake application.

It's really a hybrid of mechanical and hydraulic and can't just be left alone like single piston floating caliper as many now use.

[Skoti]

I've often wondered if the use of asbestos free organic brake pads is perhaps the cause of our brakes squealing nowadays.

Back in the 70's when I worked in the MC trade I can't particularly remember having problems with Honda brake pad squeal, but back then they were fitted with asbestos compound pads.
I do remember freeing off lots of seized caliper pivots during the winter months for customers that rode their bikes all year round.



A while back I did first try deglazing the pads as mentioned earlier in this thread and it does work but needs to be done regularly as the squeal just keeps coming back again and again.


For me and others the more expensive and grippy EBC FA013V semi sintered pads seems to mitigate this problem.
I've also got a stainless steel piston fitted, which I think is a worth while modification as it eliminates possible corrosion problems.

 






 


 

[Mikep328]

I've had no squealing on my 400F in the 2+ years since I overhauled the front brake system. It didn't squeal before the overhaul either but it also didn't stop! 

I did a thorough bedding in procedure - not sure if that helped to prevent squealing but it made a huge difference in braking power/feel.  Also, the pads were factory beveled at the edges which may also help re squealing.

FWIW I tried five different pads/types when sorting out the brakes and, as I recall, all of them had factory beveled edges.

[Ken4004]

I have just repaired the damaged thread on the fork that the adjusting screw fits into and taken the glaze off the pads as suggested so hopefully will have time to go for a ride tomorrow and the bed the pads in again and keep my fingers crossed.

[TrickyMicky]

The gap increases as the static pad wears Mick, so it must be checked every few thousand miles to keep it at max efficiency.

Both parts of the caliper are bolted rigidly together, so when pressure is applied the piston pushing on the pad forces the caliper to swing outwards until the static pad makes contact. When releasing the brake lever the piston seal returns from its distorted shape back to normal moving the piston back a fraction. If the static pad were to go further back it would pull the whole caliper with it, thereby making the moving pad come into contact with the disc again. I've never had a vehicle yet where the disc brakes needed adjusting once set up.  The biggest problem with the brake on out Hondas is tightness of movement on the swinging spindle.  The spigot needs  gentle use with fine emery cloth and then given a dollop of coppaslip.

[K2-K6]

The gap increases as the static pad wears Mick, so it must be checked every few thousand miles to keep it at max efficiency.

Both parts of the caliper are bolted rigidly together, so when pressure is applied the piston pushing on the pad forces the caliper to swing outwards until the static pad makes contact. When releasing the brake lever the piston seal returns from its distorted shape back to normal moving the piston back a fraction. If the static pad were to go further back it would pull the whole caliper with it, thereby making the moving pad come into contact with the disc again. I've never had a vehicle yet where the disc brakes needed adjusting once set up.  The biggest problem with the brake on out Hondas is tightness of movement on the swinging spindle.  The spigot needs  gentle use with fine emery cloth and then given a dollop of coppaslip.

Thats because this caliper design is unique (dont think anyone else used it at all) and definitely needs to have the adjustment manually applied to track the static pad wear. Then the screw has to be backed out again when new pads are used in replacement. It's just normal for this operation.

There's something similar in virtually all VW group car rear calipers, those having a mechanical operation of handbrake, concentric and inside the single hydraulic piston. That one ratchets itself in tracking the wear (unseen by driver) to keep pads correctly adjusted. This is facilitated by the operation of handbrake while footbrake is held down and clamping the disc, to allow ratchet mech most advantage in creeping with wear. They too need winding back out when pads are replaced.

[Oddjob]

Can’t add much to Niges explanation tbh, you do seem to be missing the role the spring is doing here Mick. It pushes the arm back when the hydraulic pressure is released. So the pad wearing means the gap continuously increases.

[TrickyMicky]

My final attempt, theoretical example, if the hydraulic piston had to move 1/2 inch before the pads make contact, due to the nature of the seal, when pressure is released the seal returns to its normal shape by retracting just a few thou. It does not travel all the way back inside the chamber, therefore, if the static pad tries to spring outwards it will pull the other pad into contact with the disc leading to binding.

[Athame57]

A chamfer on the leading edge of the pad can help.

That's what I do besides the copper grease treatment. I always called it a bevel myself. 

[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]

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/

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.