Grabby Front Disc Brake - Chinesse 50CC

[china505]

I have one of the Chinesse 50cc scooter and the front brake is grabby, is there anyway to decrease the pressure. Looks like there is a label on the fitting attached to the brake that says something about pressure but, not in my language.

Thanks

[Fox]

Just don't squeeze so hard! It'll wear down and get less "Grabby" after a while. In the mean time use two fingers instead of four. 

[china505]

Based on the label I think it has a pressure regulator where the brake hose connects to the brake caliper. There is a cap on the botton which I removed. Then I saw what looked like a long set screw which I unscrewed some, thinking it would decrease the pressure but it didn't. I assume that there is a spring above the set screw and a piston above the spring. Has anyone taken this item apart? I don't what to take it apart and have the hassle of bleeding unless needed. I'm assuming that maybe the piston is seized and not regulating the pressure. The brake is too sensitive and wasn't that way 4,000KM ago.

[Fox]

That's an "anti-lock" device. I've removed them but like you said then you have to bleed the line. At 4000 km it shouldn't be real tight. I figured it was a brand new scooter. maybe removing the pads, manually working the piston in and out all the way a couple times and cleaning the caliper up with some WD40 will solve the issue without a bleeding. ? 

[china505]

Conclusion!
The "anti lock " device is a pressure relief valve and isn't working because the caliper is moving freely. So, I took it apart and found the hole in the piston was plugged with what looked like some residual from the brake hose. The valve is on the bottom end of the T fitting, brake hose on top and the caliper on the other leg on the side. First remove the T fitting from the scooter. Caution the caliper side of T-fitting has left handed threads. To disassemble the valve you remove the valve cap, then remove what looks like a set screw with a 6mm allen wrench. Once you get the set screw out remove the spring and piston which has two o-rings. Clean the hole out in the piston and the other parts. Then remove and master cylinder cover and the rubber bladder. Flush the brake system out several times by refilling the master cylinder. Put everything back together except the master cylinder cover and bladder, then bleed the brake system. Once the system is bleed and you have a good brake install the master cylinder bladder and cover. This took care of my grabby front brake and operates like it did.  

[Fox]

 Congratulations! Nice fix. 

 All the ones I removed were right hand threaded so the fitting for the hose screwed right in.

[china505]

Where the hose screws into the T is right handed but, the threaded coupling that screws into the T and then into the brake caliper is left handed.