where to buy O-rings for brake caliper?

yippyfingers

Member
Region
USA
After riding only 820 miles on my ebike, I heard and discovered metal-to-metal contact on the rear hydraulic disc brake pad-to-caliper. One of the pads was worn into a wedge shape, rather than being worn evenly from top to bottom. The piston on that side would not retract and I couldn't install new pads, so I tore the caliper apart. Getting the piston out took considerable effort and I discovered that the O-ring was essentially glued to the piston on roughly 40% of its circumference. I had to scrape the O-ring off the piston with a knife. First question: how could this have happened? Did the caliper overheat and have the O-ring melt onto the piston? By the way, there is no groove in the piston for the O-ring. The groove is in the caliper body. Second question: is there a source of O-rings that measure in millimeters: OD = 24.5 mm, ID = 20.3 mm, width = 2.15 mm, wall height = 2.1 mm ? The cross-section of the O-ring is square, not round. The ebike company offered to sell me a new caliper, but I only need an O-ring. This caliper is very easy to rebuild, if I can just find an O-ring. I have done a thorough online search for O-rings and came up empty for this size.
 

yippyfingers

Member
Region
USA
It is a no-name Chinese caliper, very similar to a Tektro but with a different O-ring size. How would a better caliper handle heat better? My caliper has a steel piston which bear upon the steel backing of the disc brake pad, so there will be heat transfer at that point of contact. I have seen many calipers that have ceramic pistons, and I wonder if ceramic is used because it is a poor conductor of heat, thus reducing the amount of heat transferred to the hydraulic fluid and O-ring. The construction of my caliper is virtually identical to that of Volvo car calipers, which is to say that the square cross-section O-ring holds the piston just enough to let it move a bit toward the rotor during braking, and then pulling it back after the brake lever is released, even though the piston can slide through the O-ring a bit when the pads wear away.
 

fooferdoggie

Well-Known Member
It is a no-name Chinese caliper, very similar to a Tektro but with a different O-ring size. How would a better caliper handle heat better? My caliper has a steel piston which bear upon the steel backing of the disc brake pad, so there will be heat transfer at that point of contact. I have seen many calipers that have ceramic pistons, and I wonder if ceramic is used because it is a poor conductor of heat, thus reducing the amount of heat transferred to the hydraulic fluid and O-ring. The construction of my caliper is virtually identical to that of Volvo car calipers, which is to say that the square cross-section O-ring holds the piston just enough to let it move a bit toward the rotor during braking, and then pulling it back after the brake lever is released, even though the piston can slide through the O-ring a bit when the pads wear away.
They are made to deal with the heat. If you have a cheap product and it fails well there you go. my Shimano 4 position calipers can take what I need to dish out on our tandem on long decents and dissipate the heat well. they have ceramic pistons. but even Shimano pretty much will js replace the whole thing over trying to repair it. buy a decent caliper and stop frustrating yourself.
 

yippyfingers

Member
Region
USA
Are you saying that only ceramic pistons are able to deal with the heat? As far as I can tell, my calipers are copies of those made by other companies, which might suggest that other companies which don't use ceramic pistons can have overheating calipers. Have you heard of other calipers overheating and melting O-rings? Or have you heard of other calipers making the hydraulic fluid boil? The only overheating that I have ever heard of is rotors turning red hot. Please educate me about the overheating mechanism, and specifically can it make an O-ring adhere to a steel piston. By the way, I am not aware of any time that I overheated my brakes, but it may have happened. I certainly never made my rotors glow red.
 

fooferdoggie

Well-Known Member
Are you saying that only ceramic pistons are able to deal with the heat? As far as I can tell, my calipers are copies of those made by other companies, which might suggest that other companies which don't use ceramic pistons can have overheating calipers. Have you heard of other calipers overheating and melting O-rings? Or have you heard of other calipers making the hydraulic fluid boil? The only overheating that I have ever heard of is rotors turning red hot. Please educate me about the overheating mechanism, and specifically can it make an O-ring adhere to a steel piston. By the way, I am not aware of any time that I overheated my brakes, but it may have happened. I certainly never made my rotors glow red.
the fluid will heat up I see it on my tandem it gets dark and the rotor gets black gunk on it if I use the back too much at a time. but I have never had a loss of breaking power I don't let it get that far.
it could just be very cheap rubber but who knows? cheap fluid that corroded the rubber. could be they used used cooking oil in the system. I also have ice-tech 203mm rotors and finned pads to help keep it cool.
 

yippyfingers

Member
Region
USA
Don, thanks for the link! First glance, it looks like an incredible site. Rome, thanks for the tip, but I don't ride my brakes. I think that the rotor would glow red before enough heat would transfer to an O-ring, but I am only guessing. My rotor has never been too hot to touch, but maybe sometime I missed it?? Has anybody ever heard of an O-ring melting inside a caliper?
 

retiredNH

Well-Known Member
Region
USA
The OP should realize that one can copy a design (the dimensions and look) without spending money or effort on design tolerances and materials. IOW, while a cheap no name caliper may LOOK the same, it probably is NOT the same.

The OP got good advice here, especially from fooferdoggie, yet still wants to rebuild the same cheap calipers. I wish the OP luck and hope there's no sacrifice of future safety. Of course, it's only brakes we're talking about. The OP can always drag feet to stop....
 

yippyfingers

Member
Region
USA
RetiredNH, anybody with a keyboard can spew opinions, as you did, but it would better to come with data. I have asked questions that I was hoping would be answered, but mostly what I get is people guessing that my brakes are cheap and poorly built/designed with subpar materials. If my experience with what appears to be melted O-ring has happened with other brake systems, then such comments would automatically condemn those brakes systems too. Data is needed rather than guesses. Most people have never worked on brake systems and think that replacing a caliper is the only answer, but they don't realize that the O-ring and brake pads are easily replaced and we don't need to waste the resources and manpower that went into building a caliper.
 

fooferdoggie

Well-Known Member
RetiredNH, anybody with a keyboard can spew opinions, as you did, but it would better to come with data. I have asked questions that I was hoping would be answered, but mostly what I get is people guessing that my brakes are cheap and poorly built/designed with subpar materials. If my experience with what appears to be melted O-ring has happened with other brake systems, then such comments would automatically condemn those brakes systems too. Data is needed rather than guesses. Most people have never worked on brake systems and think that replacing a caliper is the only answer, but they don't realize that the O-ring and brake pads are easily replaced and we don't need to waste the resources and manpower that went into building a caliper.
I haven ever heard of the o ring gluing its self. the piston can get sticky and needs cleaned but your problem was a material failure. so far it dos north sound like its easy to replace the o ring and your bike is down till you can find one.
 

retiredNH

Well-Known Member
Region
USA
RetiredNH, anybody with a keyboard can spew opinions, as you did, but it would better to come with data. I have asked questions that I was hoping would be answered, but mostly what I get is people guessing that my brakes are cheap and poorly built/designed with subpar materials. If my experience with what appears to be melted O-ring has happened with other brake systems, then such comments would automatically condemn those brakes systems too. Data is needed rather than guesses. Most people have never worked on brake systems and think that replacing a caliper is the only answer, but they don't realize that the O-ring and brake pads are easily replaced and we don't need to waste the resources and manpower that went into building a caliper.
The DATA is that you have brakes of unknown brand, unknown construction, and unknown materials. And yes, I have worked on brake systems before, automotive and bicycle, including re-building calipers. But I only do so for quality calipers, where name brand parts are readily available.
Brakes, for me, are too important. I would not rely on an unknown part that has already shown an unusual failure mode.
You obviously have your mind made up that you're going to rebuild your caliper(s) with materials that may or may not be up to the job. (all O rings are not the same...) I wish you luck...
 

fooferdoggie

Well-Known Member
You obviously have your mind made up that you're going to rebuild your caliper(s) with materials that may or may not be up to the job. (all O rings are not the same...) I wish you luck...
exacly you have to have a mineral oil stable O ring or DOT one who knows?
 

yippyfingers

Member
Region
USA
Oh my goodness! I have a brake failure mode that is unknown to 3 people (including me) in a caliper of unknown construction, brand, and materials. Since only well-known brands can be any good, and my caliper has been proven to have those unknowns while having a problem, then I think it is ethically mandatory that the manufacturer must issue an immediate recall of all such calipers because we don't want any consumers to be dragging their feet to stop. Thank you for bringing me to this realization. I only wanted to know the source of replacement O-rings, but now I see how serious this situation is.
 

tomjasz

Well-Known Member
RetiredNH, anybody with a keyboard can spew opinions, as you did, but it would better to come with data. I have asked questions that I was hoping would be answered, but mostly what I get is people guessing that my brakes are cheap and poorly built/designed with subpar materials. If my experience with what appears to be melted O-ring has happened with other brake systems, then such comments would automatically condemn those brakes systems too. Data is needed rather than guesses. Most people have never worked on brake systems and think that replacing a caliper is the only answer, but they don't realize that the O-ring and brake pads are easily replaced and we don't need to waste the resources and manpower that went into building a caliper.
What can “no-name Chinese caliper” be other than another awful cheap design rip off. Very commonplace practice in China. Don’t be insulted. NH wasn’t critical of you. Any if us around eBikes for years have seen this time and time again. You be best off buyingva set of Tektro brakes and replacing those fake versions.
 

TrevorB

Active Member
If you do try and repair old brake and caliper leaks you'll likely to endup writing off a set of new pads from fluid contamination.

Just save yourself whole lot of grief and buy new ones. Shimano entry level MT200 are cheap from Aliexpress. <USD100 for both front and rear sets with rotors. Fit them and forget. You may need bleed kit if rear hose is to be feed through frame. Don't forget some spare Shimano original BS01 pads while you are there.

While entry level by Shimano standards they will be stepup in performance from most Chinese ones and considerable more reliable.
 

m@Robertson

Well-Known Member
Region
USA
Seems like the chances of finding an exact size match is unlikely since the manufacturer will not cooperate. And anything thats close-enough is going to need to operate *smoothly* under hydraulic pressure. Doesn't sound likely to find a fix. Especially since an approximate fit has to be installed and tested. I'd be worried about both a leaky AND a sticky piston without an exact match.

I had a mildly leaky piston on one of my Maguras and the factory replaced the entire caliper under warranty. Didn't even try to repair it. I think thats probably typical.
 

fooferdoggie

Well-Known Member
Seems like the chances of finding an exact size match is unlikely since the manufacturer will not cooperate. And anything thats close-enough is going to need to operate *smoothly* under hydraulic pressure. Doesn't sound likely to find a fix. Especially since an approximate fit has to be installed and tested. I'd be worried about both a leaky AND a sticky piston without an exact match.

I had a mildly leaky piston on one of my Maguras and the factory replaced the entire caliper under warranty. Didn't even try to repair it. I think thats probably typical.
yes Shimano tends to just replace too. far less liability that way.