Creeping brake pad drag

On Thursday, November 21, 2019 at 5:49:46 PM UTC-8, jbeattie wrote:
On Thursday, November 21, 2019 at 5:22:21 PM UTC-8, Frank Krygowski wrote:
On 11/20/2019 9:02 PM, jbeattie wrote:
On Wednesday, November 20, 2019 at 11:07:59 AM UTC-8, Andrew Chaplin wrote:
I have been riding a gravel bike (Kona Rove NRB DL https://www.konaworld.com/rove_nrb_dl.cfm) for a year now. It has developed a tendency to drag the pads of the front brakes against the disc. I recently had the pads and rotor, front and rear, replaced (about 5,000 Km of use). As I ride, a noise comes from the front brake that suggests that the pads are touching the rotor, and it increases in volume until I "blip" the lever, which makes it go away for maybe another Km or so--or less.

Has anyone encountered this before? if yes, how did you solve it?

Yikes, you must do a lot of braking. 3K miles for a rotor doesn't seem like much.

Anyway, you may just need to reset your pistons. https://www.epicbleedsolutions.com/r...liper-pistons/ If that doesn't work, then the next thing is checking to make sure the caliper is centered. Like Andrew says, just follow the instructions for installation/alignment. https://www.youtube.com/watch?v=uk_nC9anQcM&t=13s

If that doesn't do it, check to make sure that both pistons are retracting. I have a piston that will drag occasionally, and I need to clean it. Follow this routine: https://www.youtube.com/watch?v=vQXF...&feature=youtu

I just got around to watching those.

The last procedure especially seems to be a real pain. And it's required
by mere dirt? Sheesh.

Would you be truly happy if new technology were problem free, and the tedious Jute Trollfests were all we had to read? Thank god for fussy disc brakes!

Discs are not really that bad, either, and a sticky piston is about equivalent to getting crap stuck in your brake pads -- although you can't just throw in a new piston and call it good like you can with a brake pad. And adjusting cantis is worse. I can mount, fill and align a disc caliper in the time it takes to get a canti working well with STI levers, if ever.

I like my hydraulic discs and do regret getting my latest, greatest racing bike with rim brakes -- but only because my Dura Ace front rim brake track is about gone, and it sounds terrible when I brake. Even dry braking does have a rim lathe effect, although it is much worse in the wet. That's one reason why I switched to discs for my wet weather bikes -- I got tired of replacing rims. Not being able to stop well in the rain was another reason. I am sold on discs for wet weather riding. I'm agnostic for dry weather riding -- unless I were on CF rims or end-of-life aluminum rims or wanted big fat tires. Being able to put a 28mm on racing bike is kind of fun.

-- Jay Beattie.

It isn't the piston. The return spring in the lever pulls the lever back to home position and the hydraulics pull the piston back in relation. But the pads themselves are free and can float against the disks.

On 11/21/2019 8:49 PM, jbeattie wrote:
On Thursday, November 21, 2019 at 5:22:21 PM UTC-8, Frank Krygowski wrote:
On 11/20/2019 9:02 PM, jbeattie wrote:
On Wednesday, November 20, 2019 at 11:07:59 AM UTC-8, Andrew Chaplin wrote:
I have been riding a gravel bike (Kona Rove NRB DL https://www.konaworld.com/rove_nrb_dl.cfm) for a year now. It has developed a tendency to drag the pads of the front brakes against the disc. I recently had the pads and rotor, front and rear, replaced (about 5,000 Km of use). As I ride, a noise comes from the front brake that suggests that the pads are touching the rotor, and it increases in volume until I "blip" the lever, which makes it go away for maybe another Km or so--or less.

Has anyone encountered this before? if yes, how did you solve it?

Yikes, you must do a lot of braking. 3K miles for a rotor doesn't seem like much.

Anyway, you may just need to reset your pistons. https://www.epicbleedsolutions.com/r...liper-pistons/ If that doesn't work, then the next thing is checking to make sure the caliper is centered. Like Andrew says, just follow the instructions for installation/alignment. https://www.youtube.com/watch?v=uk_nC9anQcM&t=13s

If that doesn't do it, check to make sure that both pistons are retracting. I have a piston that will drag occasionally, and I need to clean it. Follow this routine: https://www.youtube.com/watch?v=vQXF...&feature=youtu

I just got around to watching those.

The last procedure especially seems to be a real pain. And it's required
by mere dirt? Sheesh.

Would you be truly happy if new technology were problem free, and the tedious Jute Trollfests were all we had to read? Thank god for fussy disc brakes!

Discs are not really that bad, either, and a sticky piston is about equivalent to getting crap stuck in your brake pads -- although you can't just throw in a new piston and call it good like you can with a brake pad. And adjusting cantis is worse. I can mount, fill and align a disc caliper in the time it takes to get a canti working well with STI levers, if ever.

I like my hydraulic discs and do regret getting my latest, greatest racing bike with rim brakes -- but only because my Dura Ace front rim brake track is about gone, and it sounds terrible when I brake. Even dry braking does have a rim lathe effect, although it is much worse in the wet. That's one reason why I switched to discs for my wet weather bikes -- I got tired of replacing rims. Not being able to stop well in the rain was another reason. I am sold on discs for wet weather riding. I'm agnostic for dry weather riding -- unless I were on CF rims or end-of-life aluminum rims or wanted big fat tires. Being able to put a 28mm on racing bike is kind of fun.

I guess I avoided the problems by sort of working up from the bottom of
your list. First, I don't ride a racing bike - which is logical enough,
because I don't race. So my bike will accept up to 35mm tires, I think.
(I normally run 28mm.)

Second, I don't ride that much in the rain. I'm retired, so it's an easy
choice. But even when I was working, your rain season is our snow
season, and my policy was to not bike to work if it was raining when it
was time to leave, or if the temperature was below freezing. (I really
do admire your dedication!)

Third, I don't use STI, so setting up my cantilevers (which are what I
have on most bikes) is probably way easier for me. I think I'm pretty
good at it.

As to the idiotic "trollfests" - Yes, discussing actual bike topics is
way, way better. Among his other mental and personality problems, I
honestly think he's psychopathic and intent on killing this group.


--
- Frank Krygowski

On 11/22/2019 9:50 AM, jbeattie wrote:

On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:


I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.


You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not horribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.


In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.


--
- Frank Krygowski

On Friday, 22 November 2019 13:01:26 UTC-5, Frank Krygowski wrote:
On 11/22/2019 9:50 AM, jbeattie wrote:
On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:

I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.

You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not horribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.

In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.


--
- Frank Krygowski

Articles that deal with setting up cantilever brakes can be pretty long too as there's a lot to it such as getting the right straddle cable length and then the toe-in. Those of us who have no trouble or very little trouble setting up or adjusting cantilever brakes often forget about the trouble we did have whilst learning to do that.

Cheers

On Friday, November 22, 2019 at 8:40:43 AM UTC-8, Tom Kunich wrote:
On Thursday, November 21, 2019 at 5:49:46 PM UTC-8, jbeattie wrote:
On Thursday, November 21, 2019 at 5:22:21 PM UTC-8, Frank Krygowski wrote:
On 11/20/2019 9:02 PM, jbeattie wrote:
On Wednesday, November 20, 2019 at 11:07:59 AM UTC-8, Andrew Chaplin wrote:
I have been riding a gravel bike (Kona Rove NRB DL https://www.konaworld.com/rove_nrb_dl.cfm) for a year now. It has developed a tendency to drag the pads of the front brakes against the disc. I recently had the pads and rotor, front and rear, replaced (about 5,000 Km of use). As I ride, a noise comes from the front brake that suggests that the pads are touching the rotor, and it increases in volume until I "blip" the lever, which makes it go away for maybe another Km or so--or less.

Has anyone encountered this before? if yes, how did you solve it?

Yikes, you must do a lot of braking. 3K miles for a rotor doesn't seem like much.

Anyway, you may just need to reset your pistons. https://www.epicbleedsolutions.com/r...liper-pistons/ If that doesn't work, then the next thing is checking to make sure the caliper is centered. Like Andrew says, just follow the instructions for installation/alignment. https://www.youtube.com/watch?v=uk_nC9anQcM&t=13s

If that doesn't do it, check to make sure that both pistons are retracting. I have a piston that will drag occasionally, and I need to clean it. Follow this routine: https://www.youtube.com/watch?v=vQXF...&feature=youtu

I just got around to watching those.

The last procedure especially seems to be a real pain. And it's required
by mere dirt? Sheesh.

Would you be truly happy if new technology were problem free, and the tedious Jute Trollfests were all we had to read? Thank god for fussy disc brakes!

Discs are not really that bad, either, and a sticky piston is about equivalent to getting crap stuck in your brake pads -- although you can't just throw in a new piston and call it good like you can with a brake pad. And adjusting cantis is worse. I can mount, fill and align a disc caliper in the time it takes to get a canti working well with STI levers, if ever.

I like my hydraulic discs and do regret getting my latest, greatest racing bike with rim brakes -- but only because my Dura Ace front rim brake track is about gone, and it sounds terrible when I brake. Even dry braking does have a rim lathe effect, although it is much worse in the wet. That's one reason why I switched to discs for my wet weather bikes -- I got tired of replacing rims. Not being able to stop well in the rain was another reason. I am sold on discs for wet weather riding. I'm agnostic for dry weather riding -- unless I were on CF rims or end-of-life aluminum rims or wanted big fat tires. Being able to put a 28mm on racing bike is kind of fun.

-- Jay Beattie.

It isn't the piston. The return spring in the lever pulls the lever back to home position and the hydraulics pull the piston back in relation. But the pads themselves are free and can float against the disks.

Huh? That makes no sense in a hydraulic system. The pistons retract when fluid pressure is reduced in the slave cylinder, and the seals spring back, pulling the pistons with them. The pads retract to match the pistons because of the pad springs. The pads are not free to float against the disc unless you trashed the pad springs.

Lots of MTB designs don't have lever return springs. https://tinyurl.com/wtumebc Even if the lever has a return spring, the return spring might affect the speed of plunger draw-back on the master cylinder (assuming some sort of rigid connection between the push-rod and master cylinder), but it is fluid pressure, vacuum and the spring (if any) in the master cylinder that ultimately pushes the master cylinder plunger back and reduces system pressure, which reduces pressure and allows the piston seals to push the pistons back into the slave cylinder. It has nothing to do with the brake lever springs.


-- Jay Beattie.

On Friday, November 22, 2019 at 10:01:26 AM UTC-8, Frank Krygowski wrote:
On 11/22/2019 9:50 AM, jbeattie wrote:
On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:

I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.

You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not horribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.

In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.

Hydraulic discs are surprisingly simple mechanical devices, but they are plumbing -- really minor plumbing. I think there is about 50ml of oil in my front brake. It's not like fixing a live water main. There is no need to adjust pad angle, straddle cable length, etc., etc. No whacking the return spring to center the brake or dealing with sticking cables (sort of a problem of the past, but if you want to reach way back to classic equipment). Nothing is as bad as a stuck or cross-threaded freewheel. The good old days weren't perfect, except in our memories.

-- Jay Beattie.

On Friday, 22 November 2019 15:40:24 UTC-5, jbeattie wrote:
On Friday, November 22, 2019 at 10:01:26 AM UTC-8, Frank Krygowski wrote:
On 11/22/2019 9:50 AM, jbeattie wrote:
On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:

I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.

You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not horribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.

In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.

Hydraulic discs are surprisingly simple mechanical devices, but they are plumbing -- really minor plumbing. I think there is about 50ml of oil in my front brake. It's not like fixing a live water main. There is no need to adjust pad angle, straddle cable length, etc., etc. No whacking the return spring to center the brake or dealing with sticking cables (sort of a problem of the past, but if you want to reach way back to classic equipment). Nothing is as bad as a stuck or cross-threaded freewheel. The good old days weren't perfect, except in our memories.

-- Jay Beattie.

I have two old Suntour freewheels here that stick. I can put some oil in them, turn them until movement is nice and smooth and the the next day they are really stiff again. In fact one gets so stiff the next day that it won;'t turn.

Cheers

On 11/22/2019 3:31 PM, Sir Ridesalot wrote:
On Friday, 22 November 2019 15:40:24 UTC-5, jbeattie wrote:
On Friday, November 22, 2019 at 10:01:26 AM UTC-8, Frank Krygowski wrote:
On 11/22/2019 9:50 AM, jbeattie wrote:
On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:

I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.

You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not ho
rribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.

In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.

Hydraulic discs are surprisingly simple mechanical devices, but they are plumbing -- really minor plumbing. I think there is about 50ml of oil in my front brake. It's not like fixing a live water main. There is no need to adjust pad angle, straddle cable length, etc., etc. No whacking the return spring to center the brake or dealing with sticking cables (sort of a problem of the past, but if you want to reach way back to classic equipment). Nothing is as bad as a stuck or cross-threaded freewheel. The good old days weren't perfect, except in our memories.

-- Jay Beattie.

I have two old Suntour freewheels here that stick. I can put some oil in them, turn them until movement is nice and smooth and the the next day they are really stiff again. In fact one gets so stiff the next day that it won;'t turn.

Cheers


Two of Suntour's most successful products, Original Winner
and New Winner, have adjustable freewheel bearings. If you
have either of those, a solution is straightforward. Tedious
yes, but less tedious than traditional 'cover plate with
shims' freewheels.

For the classic type, the correct answer is a stack of
replacement shims, a micrometer and a big pile of free time.
The practical answer is to crenellate one of the thicker
shims with your thumbnail.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On Friday, November 22, 2019 at 7:01:26 PM UTC+1, Frank Krygowski wrote:
On 11/22/2019 9:50 AM, jbeattie wrote:
On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:

I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.

You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not horribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.

In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.


--
- Frank Krygowski

If I am going to talk like this will you shoot me please because that is the moment you give up to learn and experiencing something new. I'm a mechanical engineer that started with a simple drawing board and those awful ink pens and no PC's. Then we got 2D cad, then 3D cad and then 3D cad with integrated simulation and calculation modules and databases. It got complicated everytime but is was nevertheless progress.

Lou, I like plumbing.

On Fri, 22 Nov 2019 10:19:27 -0800 (PST), Sir Ridesalot
wrote:

On Friday, 22 November 2019 13:01:26 UTC-5, Frank Krygowski wrote:
On 11/22/2019 9:50 AM, jbeattie wrote:
On Friday, November 22, 2019 at 6:01:59 AM UTC-8, Andrew Chaplin wrote:

I took it to the bike shop where I had the brake work done. They may have
damaged the seals as, after working on it and taking it for a test ride, front
braking faded quickly and there was oil leaking.

You need a different shop!

From where is the oil leaking? You can have piston seal issues as well as other issues that are relatively easy to fix, like a leaking hose connection. Other leaks can be: (1) bad internal o-ring and leaking from the seam between the two caliper halves. This was a known problem on certain RS785s, the predecessor of your caliper. I replaced the internal o-ring seal on one caliper (and now have a bag of redundant little o-rings), and that caliper woks like a charm. (2) You can also get leaking from the fill port because the stopper screw is not seating. You just pull that out, make sure the o-ring on the screw is seated properly and that the screw-seat is clean and clear. And (3) you can have a piston seal leak, which could repair itself when the piston is pushed back in. You could even have a cracked piston. Anyway, those things are reparable, although I have never replaced a piston or seal. Youtube has videos. It's probably easier buying a new caliper, which are not
horribly expensive. BTW, if you have oil on the pad, it will never work right again regardless of cleaning, sanding, etc., etc. At least that's been my experience. The pad will work marginally O.K., but I'd just buy a new set.

In general, I prefer to stay away from bicycle technologies that require
such explanations. Those include hydraulic discs. (Ten paragraph lines
of possible solutions?) Ditto for electronic shifting ("First press and
hold the button to enter the programming mode... or connect to your
computer interface using the appropriate software...") Ditto for STI,
which usually gets summarized as "You can't fix it. Just throw it away
and buy another one."

I know I'm archaic. But I like simple mechanical devices that get
diagnosed by sight and fixed with things like allen wrenches.

And I never liked working on plumbing.


--
- Frank Krygowski

Articles that deal with setting up cantilever brakes can be pretty long too as there's a lot to it such as getting the right straddle cable length and then the toe-in. Those of us who have no trouble or very little trouble setting up or adjusting cantilever brakes often forget about the trouble we did have whilst learning to do that.

Cheers

But do new bicycles now come with cantilever brakes as a standard?

If they are really just a feature of antique/classic/old junker,
bicycles, than one might suggest that those who play about with
outdated stuff should be able to adjust it themselves.
--
cheers,

John B.