A Line Inspector reported about the efforts of two Mechanics and himself to locate the cause of a hydraulic leak on the left Main Landing Gear outboard (O/B) brake that they had just changed. The CRJ-900 later returned to gate after the brake bleeder port failed at the end of the runway; just prior to Takeoff.

Narrative

A CRJ-900 returned to gate after the brake bleeder port apparently failed at the end of the runway; just prior to Takeoff.During previous maintenance activity I was asked to RII the double brake installation and Leak Check on a CRJ-900 last night (early morning). Both Outboard (O/B) brakes were changed. Mechanic 'X' and Mechanic 'Y' were working the brake changes. I observed brake changes per AMM 32-43-26; and performed Leak Checks per the General Manual. With the aircraft's hydraulic Electric Motor Pumps (ACMP) running; we got an initial leak on the left side. Mechanic shut down hydraulics and the Quick Disconnect was re-secured along with an Inspection of the left O/B brake. There was lots of fluid but we suspected fluid came from the Quick Disconnect or a stuck puck. Brake was sprayed down and I told Mechanic 'X' that I wanted him to go up to the Cockpit; turn on the Hydraulic) pumps and pump the brakes. He pumped the brakes several times for both sides and I noted there were no leaks. I also took my fingers and rubbed around the safetied bleed ports and the brake Quick Disconnect line and noted no fluid on my fingers. I feel we met the requirements of both the AMM and GMM and suspect a failed or defective bleed port. The only thing I suspect is a failed bleed port; and the only possible solution is to replace them; each and every time you have a brake change with a new one that has been through Non-Destructive Testing (NDT).DT).