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Discussion Starter · #1 ·
Hey,

I'm sure this subject has been covered several times, however, I have not been able to locate the same issue elsewhere.

Bike: 2011 Honda Fireblade, stock brakes

I am having an issue with my front brakes, what I have done so far:
1. I have replaced the brake piston seals
2. I have bled the master cylinder and no bubbles are coming out
3. Bled the brake furthest from the master cylinder, no bubbles are coming out
4. Bled the brake closest to the master cylinder, no bubbles are coming out
5. Repeated the steps 2,3 and 4 (3 times), while tapping the brakes/cylinder with a rubber mallet to help encourage air movement.

I am still unable to get sufficient pressure into the brake lever, there is enough pressure to stop the bike but the lever feels like it is moving too much.

Additional notes:
1. I have placed the brake lever under pressure overnight and I get good responsive pressure, however, this only lasts a day and returns to lower pressure.
2. The pistons are moving freely and evenly (or at least they are now I have replaced the seals)
3. When the pressure is low the bike does still brake to a safe stop, however not as responsively as they should
4. I am as confident, as I can be, that there is no air in the system so I am confused that the pressure is changing over course of a day.
5. There are no visible leaks
6. There are bulges in the pipes

I think this covers everything.

Any advice would be appreciated
 

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You may still have a bit of air trapped in the banjo fitting at the master cylinder; it can be really hard to clear them. Try this: turn the bars so that the banjo fitting on the master cylinder is lower than the rest - you may have to unclamp it to slide it over to achieve this. Then, very slowly squeeze the lever until it is at full pressure and hold several seconds. Let the lever snap back, so any air trapped in the banjo gets pulled back into the MC. You may have to repeat this several times, and between snaps, work the lever just a little to expel any air from the MC into the reservoir through the tiny holes between them.

You say there are bulges in the pipes - do you mean the flexible parts of the brake lines? If so, you may need to replace them. I recommend the stainless-wrapped type, as they flex less under pressure and, IMO, improve the feel of the brake.
 

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Discussion Starter · #3 ·
You may still have a bit of air trapped in the banjo fitting at the master cylinder; it can be really hard to clear them. Try this: turn the bars so that the banjo fitting on the master cylinder is lower than the rest - you may have to unclamp it to slide it over to achieve this. Then, very slowly squeeze the lever until it is at full pressure and hold several seconds. Let the lever snap back, so any air trapped in the banjo gets pulled back into the MC. You may have to repeat this several times, and between snaps, work the lever just a little to expel any air from the MC into the reservoir through the tiny holes between them.

You say there are bulges in the pipes - do you mean the flexible parts of the brake lines? If so, you may need to replace them. I recommend the stainless-wrapped type, as they flex less under pressure and, IMO, improve the feel of the brake.
Thank you for your response.

I made a typo and meant to say the there are no bulges in the pipes.

Just so I am clear, when when you say "banjo fitting on the master cylinder is lower than the rest" do you mean that the banjo fitting is lower than the master cylinder?

On my bike the banjo fitting is upside down, connect to the underside of the lever housing (if you Google "fireblade master cylinder", as I am currently unable to post links, you should see what I may be failing to explain) and the master cylinder is above the lever. If my understanding is correct I should just be able to slowly squeeze and quickly release?
 

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Just looked it up on Partzilla; I see the banjo bolts from the bottom, and the lever presses the master cylinder over it, with the reservoir mounted separately, above the mc. In this case, I would get the lever/mc as level as possible, with the bolt holding the banjo as vertical as possible. The banjo fitting is like a hollow doughnut, so you want to get it as level as possible. Also, make sure there are no high spots anywhere along the line - the one that crosses over looks like a possible air trap, if not routed carefully. Once all that is verified, do the slow pull, quick release.
 

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Discussion Starter · #5 ·
I've been stupidly busy, sorry for my slow response.

I released some air from the line from the pipe which arches over the front wheel and saw a noticeable improvement (which is to be expected).

No air is coming from the slow pull, quick release technique. Something I have noticed is that when I hold the brake lever overnight and the next morning the pads are not firmly pressed against the disc (I can push the bike with almost no resistance), I do however have great pressure in the lever for a time. I'm beginning to think the master cylinder needs a rebuild?

I do appreciate your advice, thank you.
 

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Well, you may still have some trapped air - that arrangement of lines looks like a real PITA to get it all out. But, the total loss of braking pressure does sound like the pressure seal in the mc isn't doing it's job. I wouldn't be surprised for it to lose some pressure overnight, but all of it signals the seal is worn or hardened from age. Make sure you check for any fluid leaking around where the lever presses on the mc, and clean it up, then get a mc rebuild kit.

When refilling the mc and reservoir, I would recommend the reverse bleed method, which involves pumping fluid backwards into the slave bleeders and up into the reservoir. Done right, this can help remove any air remaining in traps in the lines.
 

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^^^^ But watch the reservoir closely so as not to overflow. And shop rags around it to catch any bubble pop slashes.
 

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Great thread! I have been having the same issue on a '82 Yamaha XJ650 I've been piddling around with. It's been driving me crazy! All new components, mushy brake. Even tried the reverse fill method, modified. System was already filled so drew fluid out of the reservoir I pumped it into the bleed port at the far end of the system repeatedly until no air came out. More work to do sounds like.
 

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When you do the reverse bleed, you have to look at the lines with an eye for trap spots, and try to arrange them so they trap the least air, even if it means tying the line down in places. Then, there's the banjo fitting at the mc, which reverse bleeding doesn't always clear; the slow pull, hold, snap back method usually takes care of that, but sometimes, you have to cover everything and loosen it while holding pressure. Yes, fluid quirts everywhere, but the air should squirt out too. I've been lucky enough that I haven't had to do it that way, but some systems don't move enough fluid to snap the air back out.

If you're lucky enough to have a round reservoir cap, you might be able to use a pressure bleeder from https://www.motiveproducts.com/. Next time I flush my CB450, I plan to try their small universal adapter to ease the job.
 

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I bleed my brakes and clutch using a suction bleeder, makes the job a lot easier and it only cost me 10 quid.

Also once you happy you have bled the brakes pull the lever back as hard as you can and tie is there over night.
 
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