I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. However it seems I can never get rid of a slight rub on one of the brakepads in the back. When I look at it closely I can see that the rotor is perfectly aligned in the middle and when I push both cylinders all the way out I can see about a millimeter clear gap on both sides. As soon as I apply the brakes it seems that one side will not move back out but the other side will. The side closest to the wheel still has almost a millimeter gap and I can clearly see air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely touching the pad. I can see it move when braking but not as much as the pad on the inside.
Is this a feature or is my cylinder dirty or is there something I can do about it? Anybody else have the same problem?
"Per Elmsäter" <[email hidden]> wrote in :"]news:[email hidden]:
Quoted message said:
I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. However it seems I can never get rid of a slight rub on one of the brakepads in the back. When I look at it closely I can see that the rotor is perfectly aligned in the middle and when I push both cylinders all the way out I can see about a millimeter clear gap on both sides. As soon as I apply the brakes it seems that one side will not move back out but the other side will. The side closest to the wheel still has almost a millimeter gap and I can clearly see air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely touching the pad. I can see it move when braking but not as much as the pad on the inside.
Is this a feature or is my cylinder dirty or is there something I can do about it? Anybody else have the same problem?
-- Perre
You have to be smarter than a robot to reply.
I have the same problem w/ mine. It began after I bled the rear brake the last time. I didn't follow the procedures provided w/ the instructions but used the same procedure I use bleeding automotive brakes. The different procedure was used because I wasn't satisfied with the earlier bleeds. I have a theory that the fuild is under a slight pressure that prevents the pistons from returning completely.
--On Thursday, December 11, 2003 8:34 PM +0000 Al Frost=20
Quoted message said:
"Per Elms=3Fter" <[email hidden]> wrote in :"]news:[email hidden]:
Quoted message said:
I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. However it seems I can never get rid of a slight rub on one of the brakepads in the back. When I look at it closely I can see that the rotor is perfectly aligned in the middle and when I push both cylinders all the way out I can see about a millimeter clear gap on both sides. As soon as I apply the brakes it seems that one side will not move back out but the other side will. The side closest to the wheel still has almost a millimeter gap and I can clearly see air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely touching the pad. I can see it move when braking but not as much as the pad on the inside.
Is this a feature or is my cylinder dirty or is there something I can do about it? Anybody else have the same problem?
-- Perre
You have to be smarter than a robot to reply.
I have the same problem w/ mine. It began after I bled the rear brake the last time. I didn't follow the procedures provided w/ the instructions but used the same procedure I use bleeding automotive brakes. The different procedure was used because I wasn't satisfied with the earlier bleeds. I have a theory that the fuild is under a slight pressure that prevents the pistons from returning completely.
ALF
Could this be that like auto brakes, there is no return spring on the pad?=20 Automotive brakes operate on the principle that there is enough extra power =
in the motor to push the pads away. Brakes for karts (go-karts, shifter=20 karts and the like) have return springs because the motor is smaller and=20 would use a considerable amount of power pushing the pads away.
Mike Mechanical Engineering 2006, Carnegie Mellon University Remove nospam to reply.
"Per Elms?ter" <[email hidden]> wrote in :"]news:[email hidden]:
Quoted message said:
I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. However it seems I can never get rid of a slight rub on one of the brakepads in the back. When I look at it closely I can see that the rotor is perfectly aligned in the middle and when I push both cylinders all the way out I can see about a millimeter clear gap on both sides. As soon as I apply the brakes it seems that one side will not move back out but the other side will. The side closest to the wheel still has almost a millimeter gap and I can clearly see air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely touching the pad. I can see it move when braking but not as much as the pad on the inside.
Is this a feature or is my cylinder dirty or is there something I can do about it? Anybody else have the same problem?
-- Perre
You have to be smarter than a robot to reply.
I have the same problem w/ mine. It began after I bled the rear brake the last time. I didn't follow the procedures provided w/ the instructions but used the same procedure I use bleeding automotive brakes. The different procedure was used because I wasn't satisfied with the earlier bleeds. I have a theory that the fuild is under a slight pressure that prevents the pistons from returning completely.
ALF
Could this be that like auto brakes, there is no return spring on the pad? Automotive brakes operate on the principle that there is enough extra power in the motor to push the pads away.
usually, the cylinders should retract as a function of their being elastically "gripped" & sprung back by their seals. if the disk bearing is halfway decent, there's no runout mechanism for the disk to physically "push" the pads away.
Brakes for karts
Quoted message said:
(go-karts, shifter karts and the like) have return springs because the motor is smaller and would use a considerable amount of power pushing the pads away.
Mike Mechanical Engineering 2006, Carnegie Mellon University Remove nospam to reply.
I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. However it seems I can never get rid of a slight rub on one of the brakepads in the back. When I look at it closely I can see that the rotor is perfectly aligned in the middle and when I push both cylinders all the way out I can see about a millimeter clear gap on both sides. As soon as I apply the brakes it seems that one side will not move back out but the other side will. The side closest to the wheel still has almost a millimeter gap and I can clearly see air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely touching the pad. I can see it move when braking but not as much as the pad on the inside.
Is this a feature or is my cylinder dirty
probably.
Quoted message said:
or is there something I can do about it? Anybody else have the same problem?
yes & yes. i just held the "free" piston in position with pliers and worked the "stuck" one in and out a few times using the brake lever for out and a screwdriver [carefully] for in. worked fine afer that and has been no problem since - about 6 months now.
I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. However it seems I can never get rid of a slight rub on one of the brakepads in the back. When I look at it closely I can see that the rotor is perfectly aligned in the middle and when I push both cylinders all the way out I can see about a millimeter clear gap on both sides. As soon as I apply the brakes it seems that one side will not move back out but the other side will. The side closest to the wheel still has almost a millimeter gap and I can clearly see air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely touching the pad. I can see it move when braking but not as much as the pad on the inside.
Is this a feature or is my cylinder dirty
probably.
Quoted message said:
or is there something I can do about it? Anybody else have the same problem?
yes & yes. i just held the "free" piston in position with pliers and worked the "stuck" one in and out a few times using the brake lever for out and a screwdriver [carefully] for in. worked fine afer that and has been no problem since - about 6 months now.
Did you clean or lube the cylinder when it was in the out position? I have no problem pushing it in with a screwdriver. It just seems not to go back unless pushed on and normally nothing is pushing.
Did you clean or lube the cylinder when it was in the out position? I have no problem pushing it in with a screwdriver. It just seems not to go back unless pushed on and normally nothing is pushing.
no, but there was a bunch of dirt that got pushed off the piston wall as it pressed back in. i elected not to lube because shimano use hydraulic oil, so the internals are ok, and adding anything to the externals is going to retain dirt and cause abrasion. use water & see what you can get out with an old toothbrush if you want it cleaner. my view is that it's going to get messed up the next time you take it out anyway, so concentrate on freeing it up by exercising it a bit. after that, i think it will be ok.
one last thing i forgot to mention. these pistons are quite shallow. this means that pushing them back in from just one edge can easily tilt the piston in the cylinder and have it jam, particularly as the cylender wall is soft alloy. [in use, the piston hardly touches the sides and only really contacts the seals.] try and keep the piston fully square while pushing back.
jim beam said:
Per Elmsäter said:
Did you clean or lube the cylinder when it was in the out position? I have no problem pushing it in with a screwdriver. It just seems not to go back unless pushed on and normally nothing is pushing.
no, but there was a bunch of dirt that got pushed off the piston wall as it pressed back in. i elected not to lube because shimano use hydraulic oil, so the internals are ok, and adding anything to the externals is going to retain dirt and cause abrasion. use water & see what you can get out with an old toothbrush if you want it cleaner. my view is that it's going to get messed up the next time you take it out anyway, so concentrate on freeing it up by exercising it a bit. after that, i think it will be ok.
jim beam <[email hidden]> wrote in :"]news:[email hidden]:
Quoted message said:
yes & yes. i just held the "free" piston in position with pliers and worked the "stuck" one in and out a few times using the brake lever for out and a screwdriver [carefully] for in. worked fine afer that and has been no problem since - about 6 months now.
Quoted message said:
-- Perre
You have to be smarter than a robot to reply.
Just becareful not to apply too much brake lever or the unconstrained ("stuck"😉 piston may pop completely out. Then you'll have a real mess on your hands.
jim beam <[email hidden]> wrote in :"]news:[email hidden]:
Quoted message said:
Prometheus said:
--On Thursday said:
"Per Elms?ter" <[email hidden]> wrote in :"]news:[email hidden]:
> I have The 2003 XTR hydraulic discbrakes on my boing boing and I'm very happy with the brakes. > However it seems I can never get rid of a slight rub on one of the brakepads in the back. When > I look at it closely I can see that the rotor is perfectly aligned in the middle and when I > push both cylinders all the way out I can see about a millimeter clear gap on both sides. As > soon as I apply the brakes it seems that one side will not move back out but the other side > will. The side closest to the wheel still has almost a millimeter gap and I can clearly see > air ( light ) between the pad and rotor. The pad on the outside however seems to stay barely > touching the pad. I can see it move when braking but not as much as the pad on the inside. > > Is this a feature or is my cylinder dirty or is there something I can do about it? Anybody else > have the same problem? > > -- > Perre > > You have to be smarter than a robot to reply. > > >
I have the same problem w/ mine. It began after I bled the rear brake the last time. I didn't follow the procedures provided w/ the instructions but used the same procedure I use bleeding automotive brakes. The different procedure was used because I wasn't satisfied with the earlier bleeds. I have a theory that the fuild is under a slight pressure that prevents the pistons from returning completely.
ALF
Could this be that like auto brakes, there is no return spring on the pad? Automotive brakes operate on the principle that there is enough extra power in the motor to push the pads away.
usually, the cylinders should retract as a function of their being elastically "gripped" & sprung back by their seals. if the disk bearing is halfway decent, there's no runout mechanism for the disk to physically "push" the pads away.
Brakes for karts
Quoted message said:
(go-karts, shifter karts and the like) have return springs because the motor is smaller and would use a considerable amount of power pushing the pads away.
Mike Mechanical Engineering 2006, Carnegie Mellon University Remove nospam to reply.
I miss the significance of the "size of the motor" WRT to the operation of the brakes. In all disk brake systems that I am familar with the pistons return because of a reduction of pressure behind them. For example imagine a ballon filled with air. With no forces acting on the ballon the pressure is equalized across the ballon surface. If you press a finger into the side of the ballon the surface deforms and the pressure across the surface equalizes again at a higher pressure. Remove the external force and the ballon returns to its original shape. Applying this anology to hydraulically actuated disk brake systems, the increase in fluid pressure resulting from pulling on the brake lever causes the pistons to extend. Release the lever and the fluid pressure returns to normal and piston is "sucked" back into place.
I miss the significance of the "size of the motor" WRT to the operation of the brakes. In all disk brake systems that I am familar with the pistons return because of a reduction of pressure behind them. For example imagine a ballon filled with air. With no forces acting on the ballon the pressure is equalized across the ballon surface. If you press a finger into the side of the ballon the surface deforms and the pressure across the surface equalizes again at a higher pressure. Remove the external force and the ballon returns to its original shape. Applying this anology to hydraulically actuated disk brake systems, the increase in fluid pressure resulting from pulling on the brake lever causes the pistons to extend. Release the lever and the fluid pressure returns to normal and piston is "sucked" back into place.
ALF
According to your theory then something must be keeping it from getting "sucked" back in. Like a pocket of air for instance. Could there be air on one side and not on the other? Since one piston is retracting just fine and the other isn't?
I miss the significance of the "size of the motor" WRT to the operation of the brakes. In all disk brake systems that I am familar with the pistons return because of a reduction of pressure behind them. For example imagine a ballon filled with air. With no forces acting on the ballon the pressure is equalized across the ballon surface. If you press a finger into the side of the ballon the surface deforms and the pressure across the surface equalizes again at a higher pressure. Remove the external force and the ballon returns to its original shape. Applying this anology to hydraulically actuated disk brake systems, the increase in fluid pressure resulting from pulling on the brake lever causes the pistons to extend. Release the lever and the fluid pressure returns to normal and piston is "sucked" back into place.
no hydraulic system i've ever seen has relied on "sucking".
the piston doesn't slide that easily against the seal, so initial pressure is employed in moving the seal up against the "ramp". once the seal is snug on the ramp, /then/ the piston can move relative to the seal. but once hydraulic pressure is released, the rubber springing back from the ramp, with the piston hugged tightly within its grasp, is just sufficient to withdraw it to a clear position. assuming the system is sufficiently clean and the piston is free within the cylinder walls.
jim beam <[email hidden]> wrote in :"]news:[email hidden]:
<snip>
Quoted message said:
Quoted message said:
no hydraulic system i've ever seen has relied on "sucking".
The "suck" term not used in the literal sense that why it was in quotations. Hydraulic fluid is incompressable so therefore a pressure change in not part of the movement of the piston. Only the displacment of the fluid that causes the pistion to extend or retract. When the piston returns to its resting position the volume of fluid behind the piston is reduced and the piston is pulled/drawn/"sucked" back.
Quoted message said:
<snip>
Quoted message said:
the piston doesn't slide that easily against the seal, so initial pressure is employed in moving the seal up against the "ramp". once the seal is snug on the ramp, /then/ the piston can move relative to the seal. but once hydraulic pressure is released, the rubber springing back from the ramp, with the piston hugged tightly within its grasp, is just sufficient to withdraw it to a clear position. assuming the system is sufficiently clean and the piston is free within the cylinder walls.
Actually there is no movement between the seal and piston or the piston bore (or there shouldn't be any movement). The seal flexs as the piston moves and is flexible enough to not to restrict piston movement. It does not cause the piston to return to its resting position. If the piston does not fully retract one of the following conditions exist: dirt between the piston and piston bore, corrosion of the piston and/or piston bore, piston and/or piston bore wear, air in hydralic fluid or excessive fluid in the system.
"Per Elmsäter" <[email hidden]> wrote in :"]news:[email hidden]:
<snip>
Quoted message said:
According to your theory then something must be keeping it from getting "sucked" back in. Like a pocket of air for instance. Could there be air on one side and not on the other? Since one piston is retracting just fine and the other isn't?
My theory on why only one piston is "sticking" has to do with their positions in the system. The piston on the brake lever side retracts normally while the piston on the other (bleeder screw) side does not. During the bleeding process I suspect that the piston on the bleeder screw side did not fully return to its resting position. There could be a number of reasons for this but it's most likely due that the brake lever pushes more fluid that it pulls while bleeding. Once in service the piston will not fully seat due to the additional fluid behind it. Also since the only the rear is effected the bleeding process is again suspect because of the longer line (more cycles required to complete the bleed, there are no other differences I'm aware of between the front and rear brakes). One way to test this theory is to remove the pads, loosen the bleeder, seat the piston(s) and close the bleeder. This will remove the additional fluid trapped behind the bleeder screw side piston and this piston should operate normally.
jim beam <[email hidden]> wrote in :"]news:[email hidden]:
<snip>
Quoted message said:
Quoted message said:
no hydraulic system i've ever seen has relied on "sucking".
The "suck" term not used in the literal sense that why it was in quotations. Hydraulic fluid is incompressable so therefore a pressure change in not part of the movement of the piston. Only the displacment of the fluid that causes the pistion to extend or retract. When the piston returns to its resting position the volume of fluid behind the piston is reduced and the piston is pulled/drawn/"sucked" back.
Quoted message said:
<snip>
Quoted message said:
the piston doesn't slide that easily against the seal, so initial pressure is employed in moving the seal up against the "ramp". once the seal is snug on the ramp, /then/ the piston can move relative to the seal. but once hydraulic pressure is released, the rubber springing back from the ramp, with the piston hugged tightly within its grasp, is just sufficient to withdraw it to a clear position. assuming the system is sufficiently clean and the piston is free within the cylinder walls.
Actually there is no movement between the seal and piston or the piston bore (or there shouldn't be any movement). The seal flexs as the piston moves and is flexible enough to not to restrict piston movement. It does not cause the piston to return to its resting position. If the piston does not fully retract one of the following conditions exist: dirt between the piston and piston bore, corrosion of the piston and/or piston bore, piston and/or piston bore wear, air in hydralic fluid or excessive fluid in the system.
So how does the selfadjustment part come into this? What I see is two pistons, one on either side selfadjusting differently to the wear of the pads. One pulls back further than the other. When I took the wheel off and "massaged" the two pistons I could not detect any difference between the two. I could easily push them both all the way out ( kitchen knife between the pads ) and easily push them to the middle ( with the brake lever). But as soon as I start braking hard with the wheel in place the selfadjusment seems to be a little off.
"Per Elmsäter" <[email hidden]> wrote in :"]news:[email hidden]:
<snip>
Quoted message said:
According to your theory then something must be keeping it from getting "sucked" back in. Like a pocket of air for instance. Could there be air on one side and not on the other? Since one piston is retracting just fine and the other isn't?
My theory on why only one piston is "sticking" has to do with their positions in the system. The piston on the brake lever side retracts normally while the piston on the other (bleeder screw) side does not. During the bleeding process I suspect that the piston on the bleeder screw side did not fully return to its resting position. There could be a number of reasons for this but it's most likely due that the brake lever pushes more fluid that it pulls while bleeding. Once in service the piston will not fully seat due to the additional fluid behind it. Also since the only the rear is effected the bleeding process is again suspect because of the longer line (more cycles required to complete the bleed, there are no other differences I'm aware of between the front and rear brakes). One way to test this theory is to remove the pads, loosen the bleeder, seat the piston(s) and close the bleeder. This will remove the additional fluid trapped behind the bleeder screw side piston and this piston should operate normally.
Sounds simle enough. Is there no risk that additional air will enter the system by opening the bleeder?
"Per Elmsäter" <[email hidden]> wrote in message "]news:[email hidden]...
Quoted message said:
Al Frost said:
"Per Elmsäter" <[email hidden]> wrote in :"]news:[email hidden]:
<snip>
Quoted message said:
According to your theory then something must be keeping it from getting "sucked" back in. Like a pocket of air for instance. Could there be air on one side and not on the other? Since one piston is retracting just fine and the other isn't?
My theory on why only one piston is "sticking" has to do with their positions in the system. The piston on the brake lever side retracts normally while the piston on the other (bleeder screw) side does not. During the bleeding process I suspect that the piston on the bleeder screw side did not fully return to its resting position. There could be a number of reasons for this but it's most likely due that the brake lever pushes more fluid that it pulls while bleeding. Once in service the piston will not fully seat due to the additional fluid behind it. Also since the only the rear is effected the bleeding process is again suspect because of the longer line (more cycles required to complete the bleed, there are no other differences I'm aware of between the front and rear brakes). One way to test this theory is to remove the pads, loosen the bleeder, seat the piston(s) and close the bleeder. This will remove the additional fluid trapped behind the bleeder screw side piston and this piston should operate normally.
Sounds simle enough. Is there no risk that additional air will enter the system by opening the bleeder?
-- Perre
You have to be smarter than a robot to reply.
wrong
there is one chamber feeding the two pistons the problem is that one of your pistons' seals is more flexible than the other. clean and massage pistons usually fixes this. it is possible there's air still in there. it is possible that the brakes just need more time to 'break in'. double check that your brakes are properly aligned with the rotors too try shimming the calliper- the 'visible' centre may not be the centre of hydraulic pressure (for now)....
"Per Elmsäter" <[email hidden]> wrote in news:wvpDb.42279 [email hidden]:
<snip>
Quoted message said:
Sounds simle enough. Is there no risk that additional air will enter the system by opening the bleeder?
-- Perre
You have to be smarter than a robot to reply.
Providing you open the valve, seat the piston, and close the valve no air should enter the system. If you are concerned about air then slip the bleed tube over the valve before you start. This way a small amount of excess fuild will collect in the tube when the piston is reseated and you will be able to see if air enters the system (highly unlikely).
"Per Elmsäter" <[email hidden]> wrote in news:wvpDb.42279 [email hidden]:
<snip>
Quoted message said:
Sounds simle enough. Is there no risk that additional air will enter the system by opening the bleeder?
-- Perre
You have to be smarter than a robot to reply.
Providing you open the valve, seat the piston, and close the valve no air should enter the system. If you are concerned about air then slip the bleed tube over the valve before you start. This way a small amount of excess fuild will collect in the tube when the piston is reseated and you will be able to see if air enters the system (highly unlikely).
ALF
Thanks. I'll try that. I looked through Shimanos tech paper about how to bleed the brakes and I didn't really understand what went on there to be honest. I understood what they said but I kinda didn't understand what happened in the system. I guess you have to do it a couple of times first.
