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Discussion Starter #1 (Edited)
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?
 

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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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+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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Discussion Starter #4
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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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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Discussion Starter #8
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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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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Discussion Starter #10
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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If it's leaking around a caliper piston, then the seals are shot.
That can happen due to age, but also if the pistons are dirty from brake dust and road grime. Then the pistons wear out the seals.

Even though my calipers currently don't leak, I'm still replacing all my caliper seals and giving them a thorough cleaning as a precaution.
Prior to this, when changing pads, I would take an old toothbrush and scrub the pistons around the seal and piston areas.
 

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^that was what I was actually worried about. Hopefully this will be a temporary solution, but like sub mention, its probably best, for your interest as well as the bike to do a proper rebuild with new seals. If your going to do it, do it once and do it right- anonymous?


Sent from my iPhone using Motorcycle.com Free App
 

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I'm still replacing all my caliper seals and giving them a thorough cleaning as a precaution.
When did you honestly ride your Rc51 Sub?? I would think your issues are going to be from dry rot from not riding that thing....and that lovely Florida sun.:eek::D
 

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Did you get your brake issue resolved?


Mine was spongy and I replaced with new fluid and bled. Everything was all good and a week later I go to get on the bike and I can pull the lever all the way to the grip. If I pump it enough I can get the pressure built back up but its still very spongy.


i guess I'm getting air in somewhere so maybe a caliper rebuild is in my future
 

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Did you get your brake issue resolved?


Mine was spongy and I replaced with new fluid and bled. Everything was all good and a week later I go to get on the bike and I can pull the lever all the way to the grip. If I pump it enough I can get the pressure built back up but its still very spongy.


i guess I'm getting air in somewhere so maybe a caliper rebuild is in my future
Try bleeding your banjo bolt at the master first. Maybe you already did?
Do you see any signs of leaking at the caliper's pistons?
 

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Discussion Starter #16 (Edited)
I was going to report back soon, but since you asked.... I couldn't check until the forks/wheels/brakes were reattached on the bike, and then had to wait a month to see if there were any changes in lever action and feel. Now that I've done that, it seems I am still slowly getting air into the system as the lever is getting spongy and and the travel longer. I ordered new piston seals for the left caliper Monday. 8 seals (2X4) total. The quick and dirty fix didn't work for me.

It is pretty easy to check the calipers for leaks. A quick visual is likely good enough. Unbolt both front calipers and slide them off the rotors. Turn them over so you can get a good view of the inside of the calipers. My left caliper was a lot dirtier inside with a grungy wet look around the pistons. That crap also made the left fork tube dirtier, etc.

It may help to remove the brake pads as well. This is two bolts (the pins) per caliper, just remember to remove the brake pads before you unbolt the front calipers. Easy easy.
 

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Discussion Starter #17
Got my parts in today, and tonight I replaced the seals on the one caliper that had the original leak. This time there were some slivers of rubber inside the caliper. Definitely had a set of bad seals that were now letting go. We'll if the new seals fix the problem. Hope so.

I also found out that each part # had a pair of seals. Makes sense since there are two seals per piston and one seal is thinner than the other. So I now have spare seals to do the other caliper if it ever gives me problems.
 

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Discussion Starter #18
Hey, just wanted to update this thread. The caliper seals definitely went bad. No issues any more even almost a year later. The brakes rock again.
 
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