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Hello, I have been restoring an old cm400 C. I had to purchase a new master cylinder, with handle and everything, in addition to having the caliper rebuilt. Everything on my front brakes is "new" except the line. Now I can't get it to bleed. I filled my reservoir, followed the instructions to bleed, and I am getting fluid through the bleeder valve, but still zero pressure on the handle. I even bought a handheld vacuum pump to try bleeding that way and still nothing..cannot figure this out. Anyone experience this with "brand new" (rebuilt and never had fluid) system before?
 

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The caliper can trap air at times, try tapping it while bleeding. While manually bleeding this is not done like a car where you pump the brake and then open the bleeder. Bikes are done by opening the bleed, squeezing the lever, tighten the bleeder, release the lever. All done slowly.
 

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Still nothing. I am bleeding like how you said and saw air coming out of the system but now see nothing but fluid and still no pressure. Also love stays down after tightening the bleeder screw
 

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That sounds like there is an internal problem with the master since there is a spring inside to push the piston back.
 

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Hello, I have been restoring an old cm400 C. I had to purchase a new master cylinder, with handle and everything, in addition to having the caliper rebuilt. Everything on my front brakes is "new" except the line. Now I can't get it to bleed. I filled my reservoir, followed the instructions to bleed, and I am getting fluid through the bleeder valve, but still zero pressure on the handle. I even bought a handheld vacuum pump to try bleeding that way and still nothing..cannot figure this out. Anyone experience this with "brand new" (rebuilt and never had fluid) system before?
I have found with the Chinese master cylinders, that I had to bleed the master first. I did this by loosening the top banjo nut and letting the air out at the banjo nut. Then the rest was as if it were a normal master... a few pumps and flushes the system was fine...
 

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+1 on what Mike said, Bleeding the (all dry/empty) master cyllinders first is good insurance that you will be pushing fluid through your brake line. The master cylinder is the piece that produces pressure for the system, and since fluid can't be compressed, the master needs to be 'air free' to force the air out.
 

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Thanks a lot guys..that's exactly what I did to get it to work..After that no problems bleeding the system like normal. I appreciate the insight. My bike is now finished. Lubing the chain tonight and, weather permitting, her first ride since 1991 tomorrow morning :D
 
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