XS400 Front and rear master cylinder

[joey13091]

Hello everyone I have purchased new brake lines, rebuilt the master cylinder on the front and rear, and rebuilt/cleaned both calipers.

I have a few questions. What is the best way to fill the brakes from totally empty? Is the syringe fill from the bleeder screw my best bet?

Also question about the front master cylinder. In the resovoir is there supposed to be two holes? There is one clearly that you see the piston moving through it. Then there is a divot next to it. It looks like there is supposed to be a hole but there doesn't appear to be one. I've scraped it out and tried putting small pins through and there seems to be no hole.

Sorry for the dumb questions I'm still learning how to work on this stuff. Thank you in advance for any replies.

 

[joey13091]

Okay so I got the rear master cylinder bled by putting the other end of the brake line in the reservoir and that did the trick for the rear. They work great now.

I'm having trouble with the front master cylinder. When I push in the piston and let go it spits the fluid out the hole in the reservoir. Does anyone know what the issue could be. I just rebuilt it.

 

[spectra]

Both my masters were toast so I went aftermarket. Not even sure what the factory one looks like. I am sure someone will chime in soon hopefully.....

Good luck with it and hello from another Washingtonian

 

[Old Mose]

It probably has so much air in it that it can't work. I had to gravity bleed mine. Crack the bleeder slightly, you can put a short piece of hose on it and let it drain into a container of some kind. Remove the M/C top and fill it with fluid. As it disappears add more until fluid is running out of the hose. Refill the M/C and install the top and see if it works. You will probably need bleeding by pumping but just Crack the bleeder enough to get the bubbles out. Don't let a lot of fluid out, the air should be right at the bleeder! This can sometimes be a very slow process, don't rush it!

 

[joey13091]

thank you for the responses. i will try your suggestion. only thing i can think of is that i put the rubber piece on the end of the piston in the MC the wrong way. Is it normal for fluid to spit out of the hole in the MC reservoir when releasing the lever? or is that because there is air trapped inside it?

 

[Old Mose]

It isn't unheard of for a master cylinder to spit as you described. Until you get some pressure on the system I wouldn't think the direction of the rubber washer would matter but no two systems work the same. Once you get pressure on it then it would surely cause it to leak back. If you have any real doubts I would take it back apart and look but only after I had exhausted every bleeding method. Occasionally the cylinder bore is large enough that the rubber seals won't seal up but once the air is out you can add pressure by opening the bleeder and pushing fluid under pressure from a brake syringe back into the system. Close the bleeder off while the syringe is still in contact with the bleeder and then pump the brake.

 

[joey13091]

Okay. Just to clarify. The rear master cylinder looked like it had 2 holes. The front only has one correct? Every time I pull the lever and release it squirts up out of the one hole in the reservoir.

I will try the syringe from the bleeder method. Thank you.

 

[joey13091]

Is this the correct order the master cylinder goes together? Can anyone confirm?

 

[BBS360]

You've got it right. Should be a dust boot too.