Getting air into the front brake lines - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 18 (permalink) Old 11-05-2012, 07:58 PM Thread Starter
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Getting air into the front brake lines

I seem to be slowly getting air in the front brakes over time. The lever is getting spongy again after bleeding about 1 month ago. Any thoughts on where it might be getting in?

Last edited by kwtoxman; 11-06-2012 at 06:50 PM.
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post #2 of 18 (permalink) Old 11-05-2012, 09:02 PM
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When you're pulling on the brake lever, take a look at your reservoir and see if you're getting bubbles. That's usually a sign you need to rebuild your master cylinder.. $50 kit from your local Honda dealer. also, did you use fresh crush washers last time you messed with your banjo bolts? That also seems to cause issues.

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post #3 of 18 (permalink) Old 11-05-2012, 09:24 PM
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+1 Both spots that I would be checking, I always use new crush washers as I had some leak air before. No fluid pushing out but air getting in definitely.



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post #4 of 18 (permalink) Old 11-05-2012, 09:43 PM Thread Starter
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system is stock, never been touched from what I can tell (install marks line up). I haven't seen bmc bubbles, but I'll check closer. Keep any suggestions coming.
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post #5 of 18 (permalink) Old 11-05-2012, 09:50 PM
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Well if the bolts have never been cracked them my guess most likely the master...



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post #6 of 18 (permalink) Old 11-06-2012, 02:32 AM
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Unless the rubber lines are starting to fail. Then this would be an odd case indeed..... I doubt it's the lines, check all connection points. How do your pads look?


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post #7 of 18 (permalink) Old 11-06-2012, 01:35 PM
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Likely not the pads if it's repeating the issue, once maybe but once bled unless you wore the pads lots more, there should be no mushyness in the system. Cylinder rebuild, fresh fluid and then proper bleeding is relatively inexpensive (other than your time) and then you're likely good to go. Definite plus one on the crush washers. Wouldn't be a bad idea to make sure the reservoir cover is sealed properly and the diaphram and set plate are in good condition. Caliper piston seals could be worn too, just some other ideas.

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post #8 of 18 (permalink) Old 11-06-2012, 06:14 PM Thread Starter
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Most odd. I've never had this on a bike before, let alone one in such good shape with low miles.

Pads look great with little wear. I forgot the bike has crg levers. Maybe install caused a problem?

I'm going check and watch the master, clean and check the pistons, and check banjo bolt torque, doing this stuff first. And likely put on new ss spiegler lines with crush washers later. I hope the first part fixes it.
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post #9 of 18 (permalink) Old 11-06-2012, 06:17 PM
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Brake fluid breaks down over time as well as use/heat cycles and it's one of those things where the having such low mileage can actually do the opposite as far as keeping the fluid good. Bad brake fluid eats away at rubber, like the two o-rings that help to seal the brake MC piston, which may be what happened here.

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post #10 of 18 (permalink) Old 11-22-2012, 12:08 AM Thread Starter
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Well I finally got around looking at the front brakes closer. I found the problem. It appears that the left front caliper has been lightly leaking some fluid out as there was some gunk around the pistons compared to the other side. I disassembled the caliper, inspected and cleaned everything. There was no obvious problem. I decided to put it back together and see if it works as the bike is away for winter anyway. If the problem comes back (it took about a month last time to really tell), I`ll pull the caliper back off and replace or rebuild. The lever is nice and firm again.
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