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Discussion Starter #1 (Edited)
So as the title of the post says, I'll be covering what I did to bleed the brakes on my 93 CBR900RR. I'll give you a little back story first. I took of the old calipers, and just left the line hanging there over night just taped up in zip-lock bags. It was a mistake in my part as the lines had almost emptied themselves. After I had re-installed the calipers and the line, I tried for hours to bleed the brakes. I kept pumping and holding in the lever, and releasing copious amounts of air from the bleeders, but could never get a firm lever. I tried to gravity feed it over the next night, and to my dismay, there was still no firmness. I tried taking the entire lever/master assembly off, holding my finger over the hole where the banjo bolt goes, and kept pumping until only fluid shot out. I then connected it all back together and spent another hour bleeding. As you guessed, I still didn't have any success. I then used a syringe and tried back bleeding from the bleeder to force the air out. I got several air bubbles at the reservoir, but still had no firmness to the brake lever. I then tried using the syringe and tubing to suck fluid at the bleeder as if I was using a vacuum pump, still nothing. So, at this point and spending another hour just searching the web I still had nothing but the idea that the master cylinder was shot. I took it to a local garage and asked if they could assist me in bleeding. We went through a few of the same steps I did, and they told me it was a bad master. Stubborn as I am, I wasn't ready to give up and pay the $40 for used replacement. So, if you're reading this, and you're having the same problem I was, don't give up just yet. It may be common knowledge for some, but I wasn't able to find it anywhere.

The underlying problem was a combination of air trapped in the lines and at the master cylinder. Even when I tried bleeding it, the air would stay trapped.

My solution was to remove the master cylinder and lever assembly, and remove the banjo bolt supplying the main lines. I set the entire assembly aside. I then taped a zip-lock bag around the line at the very top. From there, I used the syringe and tubing with surgical precision to inject a healthy dosage of brake fluid from the bleeder valve up. When I felt confident that the first caliper was done, I moved on to the second. Once I was satisfied that the entire system below the master was free from air, I removed the line from the bag and tucked it in a way that it was upright. I then picked up the master/assembly, and with the lever pointing down and my finger over the hole, pumped it letting air out but being careful not to let air back in the hole, or through the reservoir, continued until lever was tight and only fluid was attempting to push it's way out. While holding it carefully upright with fluid at the brim, I reattached the brake line to the master/assembly. Low and behold, I had brakes. If I would have come across this post while searching for answers, I could have saved hours of my time.

This process may not be ideal for your every day bleeding needs, but if you've exhausted all your other options, it might be a promising alternative. Feel free to criticize my method, or to give me pointers. It's mainly to help others like me. The ones that might not be experts, but are too damn stubborn to accept defeat.
 

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Discussion Starter #2
C'mon guys. I've seen quite a few people have read this. If you're just a guest and new to this forum, why not register, introduce yourself and post a couple pictures of your bike.
 

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Nice write up, these master cylinders especially being over 20 years old now, can be troublesome and are often bad and can be difficult to diagnose.

For those who end up having a bad master or Caliper, there are other options out there that are bolt on or require very little modification. For example, RC51 calipers are some of the best OEM calipers to come on a bike. Those bolt right on. The RC51 master is also a larger diameter. It's just a matter of relocating the reservoir to clear the fairing stay and getting some new matching levers.

Again, good write up. Next time get some pics up with it. Thats always super helpful.
 
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