WEIRD problem with my new brake master cylinder


my nissin front brake resevoir just got hit from a big rock and now it seems to be dead, so i got another one, same model from ebay which looks in great condition. when i got it it had the lever and the brake line on it and the oil were still in, so when i pushed the lever oil came out from the hole on the other side of the brake line like it should, so i know this resevoir is defianatly in working condition.

I installed it on the bike and connected both side of the brake lines, but when i try to bleed it, nothing comes out from the nipple, but i can hear some weak "squish" sounds. also, the lever just refuse to build any pressure, i can press it through all the travel without any feeling.

so this is kinda weird, i taught maybe there is a leak from one of the brake line ends but it seems to be fine, (i think) so im clueless.

any help would be appreciated, thanks!!

Sounds to me like you just got a whole lot of air in the system, patience and it will get there.

Make sure you get (at minimum) a low budget bleed kit which consists of a piece of tube that fits on the nipple and a bottle into which the excess fluid can flow.

There's lot of info on the web on how to bleed brakes in detail, just remember that you should just keep the nipple open while bleeding the system through - there seems to be misconception on this, but it's easier that way and works just as well.

thanks, you were right, there was an awful lot of air in the system so i just needed to pump the lever a lot of times and finally the oil started to come out of the nipple. its done now.

Easiest way to get air out is putting brakfluid in thru the air nipple with pressure.

Timo McKeown

The hydraulic fluid volume is so small on these systems that the smallest amount of air can render them useless. One time we couldn't get the front brake system bled. Tried for a couple hours. Finally removed the entire system from the bike and held in up side down. For some reason bleeding it up side down worked.

I like to use a plastic syringe from the grocery store. Like the ones you use for injecting marinade into a turkey (yum). Just put a small hose on the end purge the air form the syringe and hose open the nipple and push the fluid and the air up from the caliper hose and watch the resivior fill up. It works great for getting things started or getting that stubborn air bubble out.

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