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Just finished installing some new front lines. The M/C didn't leak out while I was swapping hoses, but it refuses to pump fluid. I've never before had to bench bleed a M/C that already had fluid through it and was "in service". Is it common to lose prime like this on these M/Cs just by swappng lines?

Anyone have favorite cure? I want to avoid getting fluid on the bike so I'm not keen on trying to bench bleed the M/C and hook stuff back up. I'm thinking more like getting my hands on a vacuum bleeder to get the whole system reloaded and then try conventional bleeding to finish it off if needed.

But if plugging the M/C output and bench bleeding is the only sure way, I've got lots of rags and towels lying around ;)
 

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it should eventually bleed without bench bleeding the master. a vacuum bleeder will help and is a worthwhie investment for the future. brake fluid changes will be faster and easier. if you don't get a good bleed, hold the master level and finish with manual bleeding, then take a wire tie and use it to fasten the lever to the grip in the applied position. this will help any small air bubbles to rise through the reservoir.
 

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You probably have air bubble at top of banjo bolt at the master cylinder. Try removing the master cylinder from the handlebar so as to point it "down" at the banjo bolt. Then lightly squeeze lever about 1/2" repeatedly and the air bubble will come up through the master cylinder.

:) Chris
 

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The other thing I find that works is a trick I learned while at a shop that repaired older English cars. That is to start by forcing fluid from the caliper to the master cyl. I do this by draining the Master then using a small oil can for the fluid. It gets attatched to the bleeder by way of a rubber hose. Open the bleeder on the caliper and pump the trigger on the oil can until the resevoir gets full. Empty and repeat until bleeding is done. This seems to work well as air will have a tendency to rise naturally toward the master.
 

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I just completed putting on new pumps and 4-pad calipers on my S4R, including new lines. I would bleed conventionally till you get a fairly firm feel at the lever. After that, I find that if I zip-tie the lever all the way to the bar and remove the cap
of the master cylinder(cover w/a piece of cardboard to keep dirt out) and let the system sit for about 12 hours. During this time occassionally tap the lines and banjo fitting on master with a wrench or similar object. After the 12 hours release the lever and short stroke it a bit to get rid of the last bubbles. You will see air bubbles when you do this and you should have all the air out now.

Also, the previous post is good, do a search for EZE bleeder, it is a syringe type tool that forces fluid from the bottom up, they are cheap and I understand that they are great tools.

Good luck!
Jeff
 

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I had to use a vacuum bleeder, the kind that hooks up to an air compressor, to do the brakes on a kawasaki I rebuilt from salvage. There are just too many elbows and fittings to get all the air out by hand bleeding.
 

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You probably have air bubble at top of banjo bolt at the master cylinder. Try removing the master cylinder from the handlebar so as to point it "down" at the banjo bolt. Then lightly squeeze lever about 1/2" repeatedly and the air bubble will come up through the master cylinder.

:) Chris
that too! when air is in a high spot, it is stubborn. good tip, Chris.
 

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...I find that if I zip-tie the lever all the way to the bar and remove the cap of the master cylinder(cover w/a piece of cardboard to keep dirt out) and let the system sit for about 12 hours.
Removing the cap of the master cylinder shouldn't make a difference as far as bubbles getting through, but it will allow the brake fluid to absorb moisture out of the air. Better to keep the moisture out of your brake fluid.
 

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Discussion Starter #9
Today's Update:

Borrowed a MightyVac from my neighbor nexr door and pulled almost a pint of fluid through the system before getting all of the big random bubbles to come through. Prior to this there was not any fluid in the system because the m/c never would prime last night.

Still couldn't get any feel at the lever, but at least the m/c was primed and pumping a little bit.

Alternated between conventional bleeding attempts with some fluid coming through, but still no pressure building at the lever, and letting it sit for bubbles to migrate upstream. Occasional bubbles into the reservoir when pumping told me there was still air and it probably wasn't going to be pumped out through the bottom of the system.

After a few alternating bleeding and time-out sessions, lever feel started returning slowly. Only one more bubble spotted coming out the left caliper. No more from the right. Still really spongy.

The advice on the banjo bolt trapping air got me to thinking about the brake line splitter. When I cleaned it out last night, I noted it had bore larger than the centers of the banjos. Since it sit horizontal, I figured it was holding a good bit of air still. So I unbolted it and turned itwith the m/c end pointing up and pumped the lever about 30 short strokes. Air bubbles floated up through the reservoir. I'm sure that's at least half of the headache.

So I'm letting it sit and self-bleed for a few hours. Then, more bleeding.

The difficulty in forcing the bubbles "downhill" fast enough to get them out either by vacuum or regular bleeding is making me think about setting up a reverse injection device for next time (or to finish this job if I can't get all the air out).

Thanks for all the advice guys. I've had to use just about all of it to get the job this far along.
 
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I had a problem bleeding the front brakes also, a while back. I fhad changed out the front lever, and while bleeding the system the piston wasn't moving far enough in the master cylinder to pump fluid properly. After adjusting the little screw adjuster in the lever end, the piston was travelling over the correct distance in the cylinder to pump fluid. Took a while before I figured this out ! :-/
 

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Finally ;D

After letting it sit and self bleed for a while I went back to conventional bleeding. I ran another whole pint through the system one little squirt at the time. Man, am I glad I pulled the levers and greased the pins a couple of months ago or I would have worn them out pumping the lever that many times.

Everytime I thought I had got what little air there was out, a tiny bubble or two would sneak out through the bleeding hose. So I as I neared the end of my fluid supply I was getting no more air and decided that it was time to call it completed.

After buttoning the bike back up I went a few laps around the neighborhood testing for leaks and stopping power with some repeated hard braking. The new Fren Tubo lines don't really "feel" any different than the OEM rubber lines to me. I did notice I was getting the rear wheel much lighter on the ground without much more force on the lever as in hard braking before. I don't do stoppies or wheelies, but felt like a stoppie would be easier to do with the new lines - like only a slight more squeeze on the lever than what I was putting on it.

Thanks again for the responses and advice.
 
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