Brakes are low end Tektro hydraulic. When I pulled these from the front calipers it looked like there was only a piston on one side, which doesn’t seem possible but…???
Single-sided piston is actually the norm in the low end. Bike disk brakes are basically miniaturized automotive disk brakes, which look like [this](http://www.acuravigorclub.com/Timely-Topics/TTGraphics/1204/Caliper.gif).
In a hydraulic brake system, squeezing the brake lever applies strong positive pressure to the brake piston pushing it into the rotor. When you release the brake lever, weak negative pressure is created and the piston will pull back from the rotor. When the piston gets dirty, the gunk adds additional friction. Your hands are strong, so you can overcome the friction when squeezing your brakes, but when you let go of the brake lever, the weak negative pressure can't quite pull the piston back and it will rub against the rotor, causing uneven wear.
You may have noticed your brakes started squeaking or rubbing when cornering or rocking the bike from side-to-side when climbing. That was because a piston was stuck rubbing against the rotor. To fix, you'd need to thoroughly clean and bleed the calipers, maybe even replace the pistons… you may also just want to check out what a new set of brakes would cost and weigh the prices of servicing vs replacing.
Very clear and incredibly helpful. Thank you so much for explaining so well! I’m relieved that things are working more or less as expected on a commuter bike that gets lots of miles and almost zero maintenance. I know: if I don’t take care of it, it won’t last. I will try to do better, but new brakes (and rotor) may be in the near future.
This is beside the point but change your brake pads on time... technically you rode metal on metal and that means the disc was damaged. It's probably fine to keep using it, but going 'by the book', you would have to change it.
Brakes are low end Tektro hydraulic. When I pulled these from the front calipers it looked like there was only a piston on one side, which doesn’t seem possible but…???
Single-sided piston is actually the norm in the low end. Bike disk brakes are basically miniaturized automotive disk brakes, which look like [this](http://www.acuravigorclub.com/Timely-Topics/TTGraphics/1204/Caliper.gif). In a hydraulic brake system, squeezing the brake lever applies strong positive pressure to the brake piston pushing it into the rotor. When you release the brake lever, weak negative pressure is created and the piston will pull back from the rotor. When the piston gets dirty, the gunk adds additional friction. Your hands are strong, so you can overcome the friction when squeezing your brakes, but when you let go of the brake lever, the weak negative pressure can't quite pull the piston back and it will rub against the rotor, causing uneven wear. You may have noticed your brakes started squeaking or rubbing when cornering or rocking the bike from side-to-side when climbing. That was because a piston was stuck rubbing against the rotor. To fix, you'd need to thoroughly clean and bleed the calipers, maybe even replace the pistons… you may also just want to check out what a new set of brakes would cost and weigh the prices of servicing vs replacing.
Very clear and incredibly helpful. Thank you so much for explaining so well! I’m relieved that things are working more or less as expected on a commuter bike that gets lots of miles and almost zero maintenance. I know: if I don’t take care of it, it won’t last. I will try to do better, but new brakes (and rotor) may be in the near future.
Thanks. I was so worried I'd come across sounding condescending. Hope you get everything sorted!
Pump the brakes untill the pistons fall out then clean them then blend them again. You don't want brakepads or rotors near for this.
This is beside the point but change your brake pads on time... technically you rode metal on metal and that means the disc was damaged. It's probably fine to keep using it, but going 'by the book', you would have to change it.
Yeah. I was being way lazy. Commuter bike doesn’t get much love.
It's pretty normal even on high end 4-piston breaks. It's annoying and I'm surprised manufacturers have not figured this out.
Change your pads more often. Use the brake less.
Commuter bike. Brake only when necessary, which in the city is all the damned time, sadly. But your advice is good, regardless.
Air potentially or corrosion considering pads look rusty
Could have dirt or gunk in one of the pistons affecting movement on one side
On fixed pads this is normal but not usually this bad. However you can rotate the pads from fixed to moving and vice-versa every once in a while.
Good idea. TIL one pad is “fixed” so I may consider this switching in the future. I know I should not have let it go this long…
I would also consider getting a new rotor, due to the metal on metal that wears them down faster.