Do the pistons retract even if the wheel is not spinning? Or only when it spins?

Have you checked your wheel bearings and hub?

 

Do the pistons retract even if the wheel is not spinning? Or only when it spins?

Have you checked your wheel bearings?

I changed my wheel bearings last year and have done 3000 miles since.

Are you suggesting what wobble in the wheel is pushing the brake pads back? It could be a possibility, however I have seen how much the pistons retract even when not connected to the wheele.

 

I'd suggest actually measuring the retraction before doing anything else. Feeler gauges should be able to give you an idea of how much and how uniformly that is happening.

I know you've almost certainly already flushed the brakes with fresh fluid from a sealed container.....

 

I'd suggest actually measuring the retraction before doing anything else. Deeper gauges should be able to give you an idea of how much and how uniformly that is happening.

I know you've almost certainly already flushed the brakes with fresh fluid from a sealed container.....

I just found another use for my feeler gauges other than valve clearances, Ill check and let you know.
Mind you I have seen how much they retract when off the wheel. Some pistons move back the same amount as they move forward when I pump the lever (tested with calliper removed removed from the rotor/mounting)

 

With asymmetric pistons, I would think the distance the seals could affect piston travel would change….. but I would expect that should have been accounted for in the design stage. Assuming that is true, I would expect all pistons to have almost zero clearance when retracted.

Did you use OEM seals when you rebuilt the calipers?

 

With asymmetric pistons, I would think the distance the seals could affect piston travel would change….. but I would expect that should have been accounted for in the design stage. Assuming that is true, I would expect all pistons to have almost zero clearance when retracted.

Did you use OEM seals when you rebuilt the calipers?

Yes it was OEM, though I must says some of the pistons and internals of the callipers had some gunk, I did my best to clean and polish, but not sure if it was perfect.

 

I would suspect workmanship over materials, at this point. Not trying to knock your effort, just trying to logically eliminate the variables.

How did you clean the caliper bodies and parts? Did you have an ultrasonic cleaner available?

 

I would suspect workmanship over materials, at this point. Not trying to knock your effort, just trying to logically eliminate the variables.

How did you clean the caliper bodies and parts? Did you have an ultrasonic cleaner available?

I cleaned the seal seating in the caliper with brake fluid and a soft rag, I tried to feel any gunk with my fingers. I didn’t use an ultrasound cleaner, and I didn’t get any photos.

 

Did you get any photos of the parts you consider potential issues?

 

If it is anything like the ZX10Rs of that generation, the calipers are pretty bad. replace them with newer calipers from the ZX6 or ZX14

 

If the lever feel is correct at some point and goes seriously off in short order I would look again at how flat the rotors are and whether they can move on the buttons as intended.

remember, all of the energy you put into moving the back wheel is kinetic energy which has to be removed by the front brakes. Quite a lot of heat is involved as the pads friction transfers the energy to the rotors.

If mid they cannot expand and contract as intended, they will warp. That warp will affect the clearance between pad and rotor.

 

Are the rotors perfectly flat?
Are the buttons free and clean?

Are you actually getting all the air out of the system when you have bled them? ( I would have used a larger than 17mm piston on the master for a dual 6 piston set up, 19mm minimum)

I have a 2006 ZX6R trackbike that doesn't get used much with a Brembo RSC19/20 and lines but stock calipers and the lever only moves about 1/4" from no braking to max braking and it does that all day everyday for months on end..
So I think you are barking up the wrong tree with your assumptions and all those stupid idiots on the internets telling you to remove the dust seals and how it worked for them are just stupid fucking idiots!!!!!!!!

Are you riding this on the street, are you riding it period?????? NO- DO NOT remove the dust seals in the calipers!!

 

Are the rotors perfectly flat?
Are the buttons free and clean?

Are you actually getting all the air out of the system when you have bled them? ( I would have used a larger than 17mm piston on the master for a dual 6 piston set up, 19mm minimum)

yes i ride it exclusively on the street almost everyday to work, when its not in repair or bad weather.

my rotors are near new, with about 3000 easy miles. i put new brake fluid last year when i changed the seals.

BTW mine is a dual 4 piston setup (not the six piston one)

 

Is it possible your pads are worn unevenly? Can you measure the thickness all around? Anything that is not "parallel" between the pistons, pads, and rotor could cause this -- you can force it down, but part of it will come back up once you release pressure. Even a warped rotor could cause this when the wheel is not moving (to a smaller degree than if the wheel is spinning, which I take it from your description above is not a prerequisite to see the problem?). I assume you have measured rotor runout.

 

Putting in new fluid is different from actually flushing and properly bleeding to make sure no air in the system.

brake fluid is not a very good cleaner for coagulated brake fluid crud usually found around the machined seal grooves.... but unless they were pretty bad the minute waves in the new seal shouldn't be a problem unless it is........

 

And just because we're discussing lever movement in general, we really need to discuss/define what 'free play' means.....

Free play is the sum of all of the 'slop' in the system, as measured at whatever point of reference you want to use. With levers that's typically relative to the outermost point on the lever, and usually describes the wasted range before the lever starts doing what you want it to do. This number has a specific value when there is a cable involved, and a MUCH smaller one, when the lever is operating a hydraulic control. I'll go into that another time, we're only talking about the front brake lever in this case. Considering I've ridden bikes with cable operated drum front brakes through every generation of disc brake design...... there's a TINY amount of free play in current radial front brake designs. Practically zero.

The biggest advantage of the latest generation brake system designs is the very limited number of variables that remain. It's a similar situation to shim under bucket valve actuation; there are the least number possible moving parts.
In the case of the valves, it's just the cam pushing on the bucket (with the shim for adjustment underneath) and the springs to pull the valve back out of the cylinder. All of the motion on the valve is delivered in a purely vertical direction, because of how wide and solidly supported the bucket is that the cam is acting upon. No lateral motion involved. A piston in comparison has significantly more lateral force.

With the braking system, the radial MC has fundamentally changed how the plunger is moved to provide the force to the calipers. Earlier designs used a cantilevered system to push on the plunger, so the force applied was similar to what happens on the rear suspension with the linkage..... not linear. Every pivoting part has to have some clearance, so that it can move. Every moving part adds to the stacking tolerance of the entire system (the total 'slop'). Every lost motion in the movement of the control, is magnified by the mechanical advantage the lever is using to act on the pistons in the caliper. If there's any flex in any of those parts, it adds to the 'rubbery' feel..... if the brake lines are weak and can expand under pressure.... even more 'rubbery'.

If there is any moisture or air in the lines.... the moisture turns into steam when heated, both air and steam are compressible.... which feels 'rubbery' as well. Moisture is a particular concern because of how much more volume steam occupies compared to water..... on the order of 1,000 times more volume. Good seals and fresh fluid from a sealed container are critical when servicing brakes. Once the seal on the brake fluid is broken, the clock starts ticking. Shit can your left over fluid. Saving it for later use is a false economy.

With the radial MC the plunger acts directly on the shaft connected to the plunger, as the orientation of everything has been changed so that the lever pivot is 'outside' the arc that the shaft moves through to actuate the MC piston. It's a straight shot without any changes of direction, or lateral motion. It was initially more difficult to manufacture (and as a result more costly), but that's now a moot point as the advantage is so clear cut. (previous designs had legacy to those cable operated drum systems at some point in their past.)

Radial calipers are an incremental improvement on the preceding caliper designs, in that the friction material is more closely aligned with the rotation of the disc it acts on. The more important aspects of the caliper's design relate to how structurally rigid they are and how much of the force applied form the MC is applied directly to the pistons pushing the pads into the rotor. Single piston, sliding pin calipers gave way to double piston calipers, gave way to 4 and 6 pot designs, which sought ever better 'feel' and repeatability/sustained stable use.

Initial 'bite' occurs when the pad first engages the rotor, and rolls into the rotor due to the friction. The leading edge of the pad makes contact first, and depending on how hard you apply the brakes may remain as the primary contact point. Multiple pads in the caliper came about to expand on that 'bite'. More pads, more edges, more 'bite' area. Different sized pistons in the caliper came about, to try and eke out as much of that 'bite' as possible.

All of that 'feel' is lost, if the caliper body can flex, or the mounts are loose, or the fluid is saturated with water, or there is grunge making the pistons stick in their bores (that changes the distribution of force), the rotors are warped, the lines are weak, or something is wrong at the MC.

Everything I've discussed relies on the pads being a very small distance from the rotors when not actively being applied. If that distance is changing, it will result in a change in the distance the lever has to travel to make the pistons move to make the pads engage the rotor.

I cannot think of a reason for the gap between pad and rotor to be greater than the smallest measured value, for ANY pad/rotor measurement. The pads should skim just above the rotors, without making contact. I'd bet the intended gap is less than a human hair.

 

So if you read through the last thing I wrote on this, you have to be thinking about how far the pads actually move, and what that means for the caliper seals.... In a perfect world, the seals aren't sliding along the pistons in the caliper when the system is properly set up and operating as designed.

The total range of motion required is so short, the seals remain stuck on the same point on the pistons (and in the calipers) whether the pad is in contact with the rotor or not. All of the in and out range, is within the flexation of the seals. Their elasticity is what pulls the pads back from contact with the rotor. There is nothing else in the system which will retract the pads.

The only reason the caliper pistons do not have a groove cut in them to locate the inner surface of the seals is because the pads wear down over their useful life, and that point of contact will eventually shift slightly.

It's a tremendously simple system, executed with high precision parts. Any piston surface area which the seal comes into contact with has been protected from all of the schlock occurring 'outside' of the caliper, because it's on a one way trip 'out' of said caliper. We are very nearly our own worst enemy when it comes to limiting contamination in the caliper, as we push the pistons all the way in when we have to dismount a wheel to make it easier to get the calipers back on afterwards.

 

So if you read through the last thing I wrote on this, you have to be thinking about how far the pads actually move, and what that means for the caliper seals.... In a perfect world, the seals aren't sliding along the pistons in the caliper when the system is properly set up and operating as designed.

The total range of motion required is so short, the seals remain stuck on the same point on the pistons (and in the calipers) whether the pad is in contact with the rotor or not. All of the in and out range, is within the flexation of the seals. Their elasticity is what pulls the pads back from contact with the rotor. There is nothing else in the system which will retract the pads.

The only reason the caliper pistons do not have a groove cut in them to locate the inner surface of the seals is because the pads wear down over their useful life, and that point of contact will eventually shift slightly.

It's a tremendously simple system, executed with high precision parts. Any piston surface area which the seal comes into contact with has been protected from all of the schlock occurring 'outside' of the caliper, because it's on a one way trip 'out' of said caliper. We are very nearly our own worst enemy when it comes to limiting contamination in the caliper, as we push the pistons all the way in when we have to dismount a wheel to make it easier to get the calipers back on afterwards.

I understand this operation, its a self adjusting system. I've been dealing with this issue for a long time, here is a thread I wrote last year which you actually responded to

Finally fixed free play in brake lever 2006 636

It's been a long story of progressively improving my front brakes on the 2006 636 which use the stock 4 pot Tokico callipers, the main issue I think is that these callipers are crap which is why the ZX6R changed to Nissin callipers in 2007. I'll make a point list of every stage until the final...

www.zx6r.com

So I was happy for a while then suddenly I lost about 20% lever I think after a moderate braking (not super hard but a little more aggressive for normal street use). But at the end of the day it still that right-inner-bottom piston that is 0.5mm retracted (which from my reading is actually alot). So the suspect so far is 1. air/water 2. gunk causing a tighter hold on the piston.

 

When you bled your brakes, did you crack loose the banjo bolts both at the MC and the caliper, and not just the bleeder? You might still have air in your lines if you did not do this, regardless of how well the lever feels after a few pumps.

Are you losing any fluid? If the pistons are retracting into the caliper by themselves, how is your fluid level? Any wet areas on the calipers or lines?

Worth a check, but I'm sure you probably did that.

Might be worth re-doing your caliper and/or MC rebuild. I had to do that once and although it sucks to admit - I found my fuck-up and went on with my day.

 

Are you sure your pads are completely parallel? Did you measure at all four corners as well as the center thickness? It is a lot less likely that a piston is cockeyed, but it can happen a bit -- or there could be crud on the outer edge...

 

I'm fairly sure the pad is straight because I was able to put the feeler gauge all the way through with no resistance (against the rotor) i.e. a tiny bit of resistance with the 0.5mm but definitely no resistance with the 0.3mm one.

 

I might have misunderstood, but I thought you implied (of 8 measurements), only 2-3 measurements had a gap? So on that pad, you had both gap and no-gap, right? I assume you had two measurements per pad? one leading and one trailing? So if the leading and trailing measurements on the same pad are not the same, is it possible it is because the leading and trailing edge of the pad are worn differently? That could cause it to rock and pull back when it relaxes?

 

Ahhh here in lies the confusion. There are 8 pads… one for each piston, like little mini pads.

 

Did you try to re-use any of the copper crush washers?

 

If you mean undoing and redoing the banjo with the same washers then yes multiple times.

 

or go to all aluminum washers....but new washers could be the solution to your problem

 

The retraction is such that the whole pad wiggles in its place. In previous instances when i was working on yhe you could physically see the piston pull away from the pad.

 

I have had just about every brake problem there is EXCEPT for free play. When I was riding everyday rain or shine...I would even tually warp my rotors...Lots of hills in San Francisco. I had to clean/rebuild my calipers 3 times to get it right.

a couple of things I did not see brought up...how ae the pad pins? are the lubricated...have you checked the pad clips too and or replace them?

ARE you using the OEM brake lever?

 

I think I found the problem, when you compare the seal of the first picture (the piston that is working properly) to the second photo (a piston that is not working properly) you might notice the seal in the second photo is not seated properly.

 

Furthermore I just realised that my aftermarket MC Brembo 17 RCS is for 32mm and below calliper piston diameters and the ZX6R uses 34mm piston calliper diameters

 

That would explain long lever travel...... not enough fluid moving to move the caliper pistons. In a perfect world, the only thing happening is a very very small movement of the pistons in the caliper to make contact with the rotor, and very nearly all of the lever action gets used to transfer the force you want to apply to squeezing the rotor.