I am migrating away from my Jun Juin 4-piston calipers on my gravel bike and 29er hardtail I have set up as a bike packer.
When they work, they work well, but I am always having problems with them.
- Rapid pad wear. The pads wear too fast. Then I have to start adjusting the knob to keep them stopping with full power. Then the pistons in the cylinders are pushed out farther leading to shorter stroke. by the time the pads are worn a bit over 1/2 way, they start losing stopping power.
- If you use them a lot of long descents, they quickly heat up, sometimes boiling the mineral oil. Since I have to have new pads in them, the thermal expansion of the mineral oil causes the pistons to push out onto the rotor, making the problem worse. I've had these brakes completely lock up on me numerous times. With super hot calipers, one has to try to get them to release from the rotor in order to rotate the wheel.
- Dirt/dust rapidly builds up on the caliper adjustment knob's threads making it very difficult to try to adjust the knob out on the road/trails.
I liked them a lot, at first, but over time, I give them a thumbs down.