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If the pads are not retracting fully, it means that there is either too much brake fluid in the reservoir of the master cylinder or the fluid relief hole in the master cylinder itself is partially blocked.

You should NEVER use anything other than brake fluid to avoid contaminating the system. No oil.

Use something like a new turkey baster or a syringe to remove excess brake fluid from the reservoir.

Best and easiest way to change front and rear brake fluid is using a fluid extractor.. just time it so you keep adding new fluid while it's being sucked out without bottoming out the fluid in the reservoir. Once you see clear fluid in the extraction tube, make sure its topped off and then tighten the nipple and your golden.

Hello I agree with cheesy, and he knows china bikes very well. Good luck!

I haven't had a China bike for a LONG time but I do know about hydraulics. And brake systems are mini hydraulic systems.

Have you relieved the tension?

****The master cylinder at the lever (handlebar) is NOT adjustable. The adjustment is for setting the lever at a comfortable position (I like the levers closer to the handlebar myself).

It would not be a bad idea to just bleed the brake (at the caliper down on the wheel). It is possible that one or both of the pistons at the caliber are not retracting properly. Start with a bleed...

Attachment 28118

Put a 1/4" tube on that nipple. This will help prevent air from getting back into the caliper while you bleed it (in the pic, I have an 8mm box end wrench on the bleeder nipple). It is standard lefty loosy. BUT, do not open the bleeder valve unless you have someone squeezing the lever. AND TIGHTEN THE BLEEDER valve before releasing the lever (or air will enter thru the bleeder valve into the pistons at the caliper!). Repeat this a few times.

Most people have the opposite problem (air in the caliper pistons reducing the quality of brakes!).