Zrace XG4 - Sticky Pistons

[nanatetsi]

Hi Guys, the Pistons of the Zrace XG4 which I have on my bike are not retracting properly. I cleaned and lubed them and pushed them in and out several times. Sadly it did not help. To get them properly fixed I will have to take them apart and have a look at the seals and calipers up close. Now, my concern is if I'd have to replace the seals if there even are replacement seals available on the market. Does anyone by chance know which seals I would need or what the dimensions are? Or did anyone have similar issues with those calipers and was able to solve them? I'm evaluating if it's even worth to order a tool to open the calipers or if I should replace the calipers right away.

[Dan S.]

Hi Guys, the Pistons of the Zrace XG4 which I have on my bike are not retracting properly. I cleaned and lubed them and pushed them in and out several times. Sadly it did not help. To get them properly fixed I will have to take them apart and have a look at the seals and calipers up close. Now, my concern is if I'd have to replace the seals if there even are replacement seals available on the market. Does anyone by chance know which seals I would need or what the dimensions are? Or did anyone have similar issues with those calipers and was able to solve them? I'm evaluating if it's even worth to order a tool to open the calipers or if I should replace the calipers right away.

Are the calipers properly bled?

[nanatetsi]

Are the calipers properly bled?

I'd say yes. Braking worked perfectly for a while. After a long and steep descent the pads started rubbing. I assume due to thermal expansion of the phenolic resin pistons which made the piston stick more somehow. Since then I have the sticky piston issue. That leaves me thinking that a bad bleed is not the root cause..
In the mean time I measured the diameter of the XG4 pistons with a digital caliper which seems to be around 15.9ish mm. I found that Hope uses pistons with 16mm Diameter so maybe I could use replacement pistons from hope. Although I don't know if hope matches the diameter tolerance and if the thickness is the same..