I replaced the front brake lever on my hawk after the old one broke from some jerk tipping it over. During this process I removed the master cylinder, but I didn't take it all the way apart. I left the spring inside and just cleaned/lubricated the whole thing with fresh brake fluid. I pressed the button that is normally pressed by the end of the brake lever a bunch of times to get the brake fluid into the nooks and crannies for lubrication. The cylinder had previously been sticky with less than smooth travel, but it began to even out. Then I installed the lever into the assembly, and installed the whole thing back on the bike.

As far as I can tell, everything is as it should be, but I cannot get any pressure in the brake system. When I squeeze the lever, it's as if there is a huge air leak somewhere that's preventing pressure building up, but for the life of me, I can't figure out there. I tested the master cylinder by removing the bolt that attaches the brake lines to it, and putting my thumb on the hole. I was able to get pressure in the cylinder, and get brake fluid to squirt out, so I don't think it's the cylinder. (Though I did notice that the rubber boot on the button that gets pressed by the brake lever has seen better days.) I guess it's the lines or something else, but they were working fine before I replaced the lever. I am at a complete loss here. Any words of wisdom from you guys would be appreciated.

 

Have you bleed the air out of the lines and the calipers yet?

 

I'm guessing you need to bleed at the top banjo bolt... If you have had the system completely apart there will be a big airpocket there even if you bleed at the calipers till you become old and grey... Put a rag around it to protect the rest of the bike and bleed it like you would at the lower nipple, but careful as it's a bit more ketchup bottle effect here...

 

Upgrade, put an 01/02 GSX/R radial master cylinder on there and it has a bleed valve on the master cylinder.

No having to loosen the banjo bolt to burp the baby like the stock POC.

 

did you bleed the brakes?

whats this about bleeding at the m/c? every time ive bled brakes i just do it at the calipers

 

It just lets you get the air out of the M/C quicker, rather than having to push that air all the way down through the lines and out the calipers. You need to do both if you bleed at the M/C.. But it is quicker than just bleeding at the calipers.

 

Helps to do it the next day as well. Gives the bubbles time to rise to the top

 

The primary cup may be shot, or the cylinder bore pitted. Either will prevent pressure build-up. Since it's an aluminum cylinder, it's best to replace it. You don't want to take short cuts with the brakes, especially the front.

 

That's exactly what I was afraid of. I'll try to bleed at the MC tomorrow, but if I still can't get pressure than I have to assume the MC is shot - it was already acting really notchy and chunky anyways.

 

In that vein, anyone have recommendations for front master cylinders? Aren't a lot of folks here running CBR/GSXR radial masters? Seems like a good time to start thinking about that...

 

I didn't know there was a bleed valve on the MC. where is it? exactly? I would have used that when I swapped to the 750 calipers and MC rather than bleed it at the caliper like I did.

 

I couldn't figure out how to effectively bleed the MC and the brakes are still screwed. I have a vacuum brake bleeder - tried bleeding at one caliper, and also at both calipers at the same time, also tried bleeding the MC but I don't have a hose/tube that will go over the bolt that goes into the MC that connects the lines, so I had to remove that bolt and stick the tube directly into the MC. I was able to start bleeding the MC this way but the bubbles just never stopped - and I don't mean the little ones that sneak in around an imperfect seal, I mean huge fat bubbles.

I'm starting to think that the MC was on its last legs when I took it off and attempted to lubricate it - I probably just killed it all the way off, since it was feeling really notchy towards the end of travel of the lever.

I've got some bar end mirrors now and I love them, but, my new levers (OEM style from motion pro) are a bit too long and hit the mirror stems - especially the clutch lever. Maybe now is the time for a new MC and some shorty levers... shorty levers seem just too short though, I just need levers about an inch or so shorter than stock. So maybe a new MC and short-ish clutch lever are in order? Thoughts? Thanks for the help so far everyone.

 

I take the aviation approach to bleeding and servicing my brakes. I have a device i made to push my brake fluid in from the brake bleed port up to the reservior. Never have i ever had any issues with air in the system. Never bleed, just service once.

 

That's an interesting approach - I guess if you leave the reservoir cap off while you do that, then any bubbles that might sneak in at the bleed port would just rise to the surface of the fluid in the reservoir, pop, and be gone. Where could I get one of these "reverse" brake bleeders, short of making one myself?

 

Not sure where you could get one, but i made mine from a heavy plastic clear container. On the bottom, i installed a 1/8 bulkhead fitting with a hose that will attach to the bleed port on the brake caliper. On the top of the container i place a pressure regulator to the cap so i could limit air pressure to about 8 to 10 psi. I fill container with brake fluid and apply air from compressor. Brake fluid will flow pretty quickly. Just make sure to keep fluid level above the lower fitting so that you do not introduce air into the system. You can change the brake fluid in the front and rear in about 5 minutes.

 

Yes, leave the reservoir cap off. As long as the fluid level never gets below the lower bulkhead fitting, you can not induce air.

 

Please excuse me if I am wrong, but it appears from your comments that you are missing some fundamentals of brake bleeding.

Fill master cylinder with brake fluid.

Loosen banjo bolt on m/c. Only a small amount, maybe half a turn.

Squeeze lever a very small amount so that fluid comes out the loosened banjo. You are trying to get any air out, so that only fluid is coming through.

When no air is coming out, tighten the banjo before you let go of the lever. If you let go of the lever before you tighten the bolt it will suck air back in. This is critical. You need to be squeezing the lever and tightening the bolt at the same time.

Then you can move on to the calipers to bleed them.

 

Excused. I am definitely a novice with brakes.

Fill MC - I'm unsure of the best way to do this. It basically has two openings: where the reservoir connects, and where the banjo bolt goes in. Do you mean, fill the MC while it's off the bike by pouring fluid into the threaded opening for the banjo bolt? Then remount MC and screw banjo back in?

Back out banjo bolt half a turn, then squeeze lever to get air out - how will I know when no air is coming out without having a hose attached to the banjo? Again, I don't have a hose big enough to go over the banjo bolt. I guess I should get one.

It's 6:52am and I'm about to go to work so maybe I'm just being REALLY dim here and missing something obvious.

 

No... back up, back up... Put everything together... Like it's supposed to be when operating, all hoses and all other parts in place... That's the starting point...

Now take the cap of the reservoar close to the MC and fill it a bit above the line marked "upper" (not completely full but just about)... Squeeze the lever gently (and by using the word gently here I mean firm pressure but not "ka-thonk" because then you will get brake fluid all over you...) You will see fluid going into the system... Now the MC works the way that now it blocks off the system, nothing going in any direction...

Open the Banjo bolt just barely (hose in place) with the lever held in... Remember, rag around it catching any spill... Either you get air escaping, then close the banjo and then release the handle... If so repeat... When you get only fluid coming out, you are done... All the time keep a close eye on the reservoar... Once it gets below half, refill it... if you draw in any air here you will have to start over...

Next step is bleeding at the calipers... If you have the stock lines you have a "T" line... Bleed one caliper at the time... left-right-left-right...

Squeese the lever, hold it, open the bleed bolt and watch the bubbles... Close the bleed bolt, then release the handle and repeat... again keep the res topped of at all times...

When you don't get any airbubbles in any bleed bolt, you are done... At this point the lever should feel firm and your brakes should be back to normal...

I'm fairly sure the MC is in perfect working order... Just need to get all airbubbles out... An airbubble acts as a spring in there... When you squeese the lever it compresses and the calipers won't move... And the lever feels spongy...

 

Actually I have SS lines, and they both attach to the banjo bolt at the MC. I have a vacuum bleeder that can attach to both bleeder nipples at the calipers at the same time, but it's kind of a bitch to do it that way. I assume I can still bleed one caliper at a time (after the MC is bled) or do I have to do both lines simultaneously since they both attach to the banjo bolt?

 

Yep... Your lines is the same as stock in that respect... There are others that go from MC to one caliper and then on to the other...

 

Liquid:

When in doubt Google, http://www.youtube.com/watch?v=wIlo5ck8jg4

Besides this video, there are several others you can watch. Doing this for the first time, make it easy on yourself and get someone to help you.

Regarding bleeding the banjo bolt at the brake lever, all you are doing is loosening the bolt so you squeeze fluid out when you pull the lever in....gently and not all the way to the grip. Once the fluid squeezes out tighten the bolt and bleed each caliper separately using your vacuum system. Again, when you release the bleeder bolt, gently squeeze the lever but not enough to touch the grip; otherwise, you run the risk of introducing air into the line before you tighten the bleeder bolt. Make sure you pump the lever 15-20 times before releasing the bleeder bolt. It has taken me upwards of 25 minutes per side to get all the air out of the system. When the lever gets firmer you are almost finished with that side.

Look over the videos to get a general idea how to bleed the brakes. It is easy but it does take patience and time.

Good luck.

 

Thanks so much for the info and help, guys. Tweety and Reaper especially. Bled the MC according to your instructions and was able to start getting air out of the system. There is still some air in the lines themselves (I plan on setting aside a good solid hour of bleeding time next week) but the feel at the lever is not too terrible and the brakes work safely. It's funny, I've bled brakes many times before but I've never had the MC off the bike - always cool to learn something new about wrenching.

This was the last thing I needed to get her back on the road - it's been 8 months since I've ridden regularly. Now I'll be riding the rest of the summer. Life is good.

 

Sounds like you are on your way to having it fixed then.

You bleed the calipers one at a time. A vacuum unit makes it much easier, but I always finish off with a manual one man bleeding unit. I found the vacuum unit never allowed me to see a bleeding line full of fluid, which is good to know there are no more air bubbles coming out. When you see no more bubbles you know you are done. My vacuum unit has the line full of air all the time, so when I think I am done I change over to a manual unit to check it.

I also found the best result was obtained by doing each caliper at least twice, just alternating between the two of them.