I am defeated!

[LarryC]

I received my new braided brake lines yesterday. I have previously rebuilt the master cylinder. I just cannot get pressure in the lines! This is an N model- only a single front disc. I have blown air thru to verify free flow. I then attach to the MC and.....nothing. I suck my brains out on the hose to the bleeder while my son in law pumps away on the handle. Nodda. Take it apart- get good pressure from the MC- reassemble and.... NOTHING!!!!!!!!!!!!
I put the banjo from the MC end into the brake fluid jar and draw the lines full then reattach to the MC.........NOPE!
I found a thread in which a member used a....female's best friend to cause the air to bubble up. Not having one handy, I used an orbital sander. Not a bubble! I am stumped! I've been wrenching on cars and bikes for 40 years and I have NEVER had this kinda problem with hydraulic brakes. And to think- after pushing out the frozen piston and rebuilding the caliper- I GET TO DO IT AGAIN!!!!!!!!!!!!!!!!!

[Dogma]

You did say that you can't build pressure right? That tells me the problem is in the master, not the caliper. Try pulling fluid through the bleeder at the caliper using a big syringe (baster?) and a piece of tubing. Or get a Mityvac. (I wouldn't want to attempt to siphon brake fluid.) This will pull any air bubbles out of the master cylinder.

[SVSooke]

I have found using the MC banjo as a bleeder works every time.

[Rover]

Perhaps your master is scored or pitted inside...was it rusty?

[Agemax]

try fitting the lid on the MC while pumping the lever. i have found this helps when bleeding stainless lines. obviously you will have to remove it every few pumps when the fluid starts moving to check the level

[resjudicata]

So, you rebuilt the master cylinder and now it doesn't work?

Sounds like you done some mechanic work in the past so this may sound silly. But, are you sure you reassembled the rubber parts of the master cylinder correctly? One of the local guys rebuilt a master cylinder and couldn't get it to work. Turns out he put the rubber parts in wrong do the umbrella wasn't sealing to push fluid.

Just a suggestion.

Chris

[LarryC]

HAH! Turns out I just don't suck that much! Uhhhhh.... I mean I just couldn't provide enuff suction. I thought I did but then tried a vacuum thingie off of a weed killer sprayer. That did the trick! Popped the piston out and found it all pristine inside. A little dirt but otherwise brand shiny new lookin! Since my repair parts are the wrong size I'm gonna put it back together and try it on the theory that the plugged lines or bad MC was the original problem.

[dueller]

I've heard of guys tying the brake lever to the grip overnight to let any air bubbles to settle out overnight and then they can be pulled back into the resovoir. Might be somethin to try.

[LarryC]

Oh that weed killer spray nozzle thing is a secret weapon! I used it long enough to draw the reservoir down below the low mark 3 times- then tried the handle. First 3 pumps pushed the piston out and took up the slack. Then it firmed up. Its actually a little farther from the handle than I'd like. And firm? Wow- I didn't even need to do any pump/hold/bleed cycles at all! Took the bike for a test ride and- yowsa! I gots goooood brakes!

[Dogma]

Nice hack. Good one. The brake fluid didn't melt it, then?

[jwhelan65]

Been down this road, try taking a seringe and filling the lines with brake fluid, air compresses and with a pump as small as it is it will take forever to bleed the lines if you dont. I mity vac works best to pull fluid through.

[LarryC]

A P.S. to this thread. I don't put many miles on- just short jaunts mostly- so my work didn't get a real test till yesterday when I went on a 200 mile ride. I made a short washroom/get a drink stop about 80 miles out and when I got back on the road my newly rebuilt and bled to the max front brake was dragging. Turns out I had too much fluid in there! I opened the bleeder and released a few cc's of brake fluid to ease the pressure and all is good! Actually stops a little stronger now too. And there is actually a little play in the lever b4 any braking action occurs. So- it is possible to get the system so full and clear and air free that it can apply braking action when the system warms up. No rubber lines to expand and absorb that pressure either.

[mike_of_bbg]

This is a likely sign that your master cylinder return port is blocked. If there's too much pressure in the system it should be able to bleed back out through the return port back to the reservoir when the brake is not being applied.

Did you clean that port out when you rebuilt your MC?

I made a short washroom/get a drink stop about 80 miles out and when I got back on the road my newly rebuilt and bled to the max front brake was dragging. Turns out I had too much fluid in there! I opened the bleeder and released a few cc's of brake fluid to ease the pressure and all is good! Actually stops a little stronger now too. And there is actually a little play in the lever b4 any braking action occurs. So- it is possible to get the system so full and clear and air free that it can apply braking action when the system warms up. No rubber lines to expand and absorb that pressure either.

[LarryC]

Yeah it was clear. I could see the piston moving. There can't be anything in there large enough to block it. When the pressure built up there was no movement to be had in the lever- the piston was up against the caliper.

[Steve]

Yeah it was clear. I could see the piston moving. There can't be anything in there large enough to block it. ...

That sounds more like the "feed port" than the "bleed port".

There are actually TWO ports in the bottom of the reservoir. The one I think you are referring to is the larger of the two, might be a couple millimeters across. There is another one ahead of it that is just a small fraction of a mm across, just barely big enough for a strand of fine wire. You really can't see anything through it. In fact, on some bikes, it's under a small tab in the reservoir, so you really can't even see it.

With the master cylinder piston in the 'relaxed' position, the bleed port is open to the brake lines. As the bike moves, friction of the pad on the disk will warm the fluid, expanding it slightly. The expanding fluid goes through that very small port, into the reservoir. As soon as you barely pull on the brake lever, that port is closed off, giving full pressure to the calipers. If that port is blocked, the expanding fluid can only push on the pads, applying the brakes.

.