Brake line change, what if my master cylinder goes dry?

Mythos

Registered
I see my busa has a brake bleed down on each caliper. There is no bleed on the master cylinder. I know if I do not empty the master cylinder by bleeding it dry, it is going to empty itself when I take the banjo bolt out to change brake lines.

My concern is --how difficult will it be to get fluid flowing through the master cylinder after it has been completely drained?

Normally people try NOT to let the MC go dry so that it does not need to be bled.
 
When you drain it completely to swap the new lines, you will be filling it almost 3 times to bleed the lines.
The use of a vacuum pump gets the job done. :thumbsup:

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A vacuum pump works wonders but you can just gravity bleed the MC. Once you have everything reassembled just pour in the new fluid. Open both caliper bleeders and leave the cap off the MC. The fluid will flow through gravity down through the MC, once you get the first hint of fluid from below close the bleeders. Very, very slowly pull the brake lever back some. Be careful and slow because it will spit fluid up and everywhere. You'll possibly see a few bubbles come up, stroke the lever a few times until no air is seen up top. Again, very slowly and don't worry about pressure or feel. Stop once you feel pressure or hit the grip.

Once it's clear up top you can now bleed normally. Fill the MC, put the cap on, stroke it three times and open one bleeder. Repeat until the first bleeder is clear then move to the other. Check your fluid level every third or fourth time you open the bleeders or you'll be starting over.

You may have to crack the lines up top to get the last remnants of air, once done bleeding you can have an assistant hold the lever down under moderate to a little light pressure. Put the wrench on the banjo bolt, wrap a rag around the works to catch fluid but where you can just see the washers and lines let the air out, break the bolt loose slowly. You'll only have to do that once but checking again doesn't hurt. The guys that say to zip tie the lever down over night, that's the air they're getting. Under compression and left that way the air turns into smaller bubbles, moves into the MC and comes out when you turn the lever loose.

I personally have a reverse bleeder, it feeds fluid under pressure from the bottom up chasing the air out naturally, they're usually the best but pricey, usually 3-4X a vacuum setup like above.
 
I use a large syringe to push fluid from the caliper to the master cylinder. Then I crack the line at the master cylinder, and while covering the line with a rag, pull in the brake lever. I do this several times until you quit hearing air. Then I bleed it normally at the caliper.

The syringe trick saves me a TON of time bleeding, by pushing most of the air up, where it naturally wants to go.
 
A vacuum pump works wonders but you can just gravity bleed the MC. ..........

I personally have a reverse bleeder, it feeds fluid under pressure from the bottom up chasing the air out naturally, they're usually the best but pricey, usually 3-4X a vacuum setup like above.

We have one of those that can be borrowed for a returnable deposit from the local Advance Auto. I have used it on my other bike. It can be set to draw or expel. I will try the bottom up routine. Thanks toall of you guys and any other comments much appreciated.

Sounds like the " carefully actuate lever and watch for bubbles in the reservoir" trick does the same thing that a bleed valve on the master cylinder would do.
 
I see no more tiny bubbles rising in the reservoir.

The fluid is coming through the plastic hose clear of air bubbles on both front caliper bleeds....

I have brake pressure in the lever....pretty stiff but if I squeeze with both hands, I can pull it back to the grip (maybe I could do it with one hand if I put all my muscle into it??).

Sorry, been a LOooooNGGG time since I rode the busa and this is the only time I ever bled the brakes. Can't remember how hard the brake lever felt before I started this.


Is this thing bled properly?? ..or do I keep bleeding???
 
It should feel pretty solid after a certain amount of squeeze, like you can't squeeze it anymore. If you went with braided lines it should have less squish, if you went with rubber line then they'll still have a bit of squish even if bled properly from line expansion. If you get no more bubbles and their pumping up fairly solid I'd say your good.
 
Yup...thanks Rothman. I think you are right. The lever feels pretty stiff. A careful test run will tell if the brakes are definitely bled. My other bike is like it has brakes that came off a freight car. You don't pull much before you are doing a stoppy or locking up.

i went with SS braided lines. Past experience with this mod tells me it prolly will not make a huge improvement but looks cool and saves a bit of weight.

I see now that one line hits the dash when I turn (had the dash removed when I installed the lines). I hope I can loosen up the banjo bolt just enough to turn the fitting without letting any air in. I'm thinking should be no problem since there is pressure in the system, not vacuum.
 
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