[gal8x]

Out of the blue my rear brake line is sucking air, a steady stream of fine bubbles. gone over the line connections replacing the washers. Checked push rod distance. Disassembled master cylinder, all is well and in spec. I am at a loss. I need to know what is wrong so I can fix it I refuse to replace everything. I need to know what is wrong. what would be the most common issue?

[JimDirt]

Did you run the brake cylinder dry somehow ??

If not , there had to have been a loose fitting and/or something should have been noticeably leaking to get air in the system as its pretty much sealed , that is almost the only way ,unless the inside seals went bad , its not uncommon from riding in the dirt/mud , its a known complaint on these forums , they have rebuild kits here i think , and/or at any Honda Dealer , but i am guessing maybe some dirt got past a seal , and then either fell back out or is still in there behind the seal , if the accordion boot at the slave by the brake pedal is torn or not secured properly it will let dirt get by , there are not many things it can be

Also usually when bleeding any modern dirt bike you need a vacuum canister/pump , you can get them at Harbor Freight Tools for around $20 , well worth the price , , if no HF near you , then you can get them here , or at any Auto Parts Store and is almost mandatory to get all the air out of a CRF brake system

[gal8x]

Fixed.
This ordeal all started when the rear brake suddenly became too weak to lock up the tire. Don’t know for certain where the air came from but the line is bleeding out normally. But the weak performance persisted. Turns out the brake pads I was using have a small stud on the top which was pinching the pad spring, preventing the pads from gripping the rotor fully.

[JimDirt]

Glad to hear you figured it out !!