Topic: Rebuilt master cylinder and still no brake

[Rollthelosingdice]

I don't understand on my 79' CB650, I rebuilt the master cylinder from an ebay kit. I even tore it back down and cleaned the grease off the second time, still nothing. It's like the brake fluid isn't even being released. It cleared it very clean with a compressor and soaked it in a ultrasonic cleaner. Anyone have any ideas?

[Don R]

 Did you bench bleed it or at least bleed it at the outlet fitting to get the air out enough so it can pump?  Also check to be sure both holes at the bottom of the M/C reservoir are open. Then you can bleed the caliper. 

[bryanj]

To bleed the master first put on good quality neoprene glove then put a finger over the banjo outlet and pull in lever, lift and replace bajo finger then release lever and reaply. Repeat till fluid pressure pushes finger off banjo hole then quicly refit pipe and bleed to caliper. DO NOT DO THIS WITHOUT THE GLOVES as brake fluid WILL give you dermatitis

[Rollthelosingdice]

Also check to be sure both holes at the bottom of the M/C reservoir are open. Then you can bleed the caliper.

Don is right, the small return hole in the reservoir is likely the issue. Rebuilding the piston is great, but if there’s dried up brake fluid in the circuit, it will never develop the pressure as it can’t return the fluid to the reservoir.

Carefully remove the cap, protect your paint, and squeeze the handle. Do you see any tiny bubbles in the reservoir? No, remove the reservoir and drain it. Then carefully poke a small gauge wire into the holes to help clear them. Add some fluid off the bike and test again for circulation. If not, replace the reservoir. They’re cheap enough and your brakes are critical to work properly.

When I squeeze the handle with fluid in it, I see small bubbles start to form at the 2 holes. But I'm still not getting anything to come out of the "banjo?" hole.

[przjohn]

When you rebuilt the Master are you sure you put the piston on the rod in the right dorection? I have made this mistake and you will get nothing. Check an assembled parts diagram against the way you put it together.