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Discussion Starter #1
Greeting everyone! I own a 2016 which I maintain myself. I changed fluid after the first six months of ownership as part of regular maintainance, I've subsequently been replacing the fluid every 6 months or so as the front lever will get spongy and have an overall rough feel. Bleed it and it all goes back to a perfect feel. No leaks and everything is tightened back down. I bleed the furthest caliper first, new bottle dot 4 every time. Close off bleed nipple and rise with distilled water. Next the closer caliper, same procedure, last bleed the master cylinder. Fluid when spongy is pretty clean and looks pretty clear for 5,000 miles maybe just a LITTLE dirty, but not milky or anything that would sound an alarm. I just keep thinking there's got to be something contaminating it. Maybe a bad seal? I've checked and it looks like there are no holes in the bladder in the reservoir and the bladder does what it's supposed to be doing separating fluid level from air in the reservoir. Just reaching out to see if anyone has experienced this first hand. Thanks!!
 

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I had a similar problem with my previous VFR800. It was an older bike. I'd bleed it, it would feel great for a bit, then slowly deteriorate to slightly spongy.

I rebuilt the front brake master cylinder, and that helped a lot. Later I replaced the front brake lines (it was closing in on 10 years old). That helped even more and the solid brake feel stayed.
 

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You have to be very careful while you're bleeding the brakes to keep the fluid level in the reservoir high enough such that working the lever does not suck in air. If you let the fluid level drop too low - even if the level is higher than the drain hole - just the suction from working the lever could be strong enough to suck down air.

Try squeezing the brake lever and keep the lever squeezed in overnight. You can use rubber band or velcro strips, whatever it takes to keep the lever pulled in toward the grip. If there is air bubbles in the line, that should allow them to float to the top and out the drain port.
 
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Discussion Starter #4
I'm certain it didnt have air trapped in the lines. I'm going to zip tie the lever tonight and see of it helps. Then rebuild or maybe replace the master with a zx10r lever
 

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My stock 2012 did the same thing. It was brand new. With the zip type thing, mine was good for about an hour. A good one will hold all night, and longer, like you are saying. I thought about a rebuild. Master cylinders are really easy to rebuild, but the odds of bad seals in something that new didnt sound like it was worth investing 50.00 in for the kit.

The 2010-2015 /older zx10 used the same master cylinder. That list is long...zx6, versus 1000, etc. Maybe you'll get a good one? If you go to the kawasaki parts breakdown and look at the master cylinder, this master cylinder has been used for a LONG time.

The 2016 and newer zx10 has a nice Brembo master, but it's too small for the stock calipers. Find one from the 2010-2015 if you stay within the Kawasaki family, which is what we have, already.

The 18x19 oem brembo, from a Ducati, will work much better. You can get one of those for 150-200. Ducati used that size on a lot of bikes, before 2012. Figure 2008-2011 era. I'm not sure that's a great option now. It was, in 2013, when they were new. Mines still good, but you cant get a rebuild kit for any of the modern brembo master cylinders. It will pretty much be garbage when/if it fails. The newer stuff with the brembo m50 calipers uses a small master cylinder, like the new zx10, that's not quite matched up to our calipers. Let me know if you find a good, cheap option.
 

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Discussion Starter #6
rcannon409. I was thinking maybe a bad seal, but didnt see evidence of any weeping or residue. I do believe that would be the most likely candidate for replacement, or rebuild. I see there's an 11/16 stamp on the bottom of the master. I assume this is the bore diameter. I'll do a little leg work on if there's a suitable replacement and if not, I will just get a take off on ebay from a wrecked bike. Thanks for the info! That is a huge help
 

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What worked for me was zip tie + tapping the lines during bleeding. Just like how they do it in the medical field where they tap/flick the iv line. I had the same problem in the past but the dealership tried tapping the lines before they let me spend on a new seal. Been doing that ever since.
 

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11/16" works oit to 17.45mm , so yes, that's the size. That 18x19mm brembo I have would be a good match, so would that brembo rcs 19.....or rcs 17.

. There are two seals on the master cylinder piston. It would be very possible to have a bad inner seal, but the outer seal would prevent it from leaking. I should have tried rebuilding mine, but that kit was 50.00. The inner seal separates the high pressure side from the low pressure side. That's probably the issue.

Maybe it's worth a try with a rebuild? This kit will work. It cant be any worse than stock? https://www.allballsracing.com/18-1062.html

For 25.00, it's worth trying. The only special tool you need is a set of snap ring pliers, internal, that will handle a snap ring that's about 1/2" diameter. Even Harbour freight stuff would handle this specific ring.
 

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Two things - tying off the brake lever overnight helps, sometimes. Last time I had your issue, I found a slightly leaky crush washer on one of the brake lines. I found it be pure chance - I was refilling the lines and when I let off the lever I heard the tiniest sucking sound. I ended up replacing the crush washers in the line and that solved the issue.


You can try pushing fluid up from the bottom - that sometimes works better with some motorcycles.



Finally, use rubbing alcohol to clean up after the brake flush. It will do as good a job as the distilled water, but will dry a bit quicker. Don't use it in the brake system as (if you read the bottle) its 95% water. If you can get your hands on some real isopropyl alcohol (100%) that works really well for brake fluid clean-up. Benefits of a spouse who works in the sciences, if anyone was wondering.
 

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My bet is you are experiencing dissolved air in your brake fluid. After 6 months, the air has come out of solution and you now have a bubble. Most likely your bleeding procedure is somehow aerating the brake fluid. Just re-bleed whenever they get spongy. Zip tying overnight also helps as the compressed micro bubbles can move up to the reservoir easier.
 

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Discussion Starter #11
I decided to buy a rebuild kit from all balls racing for around 24$ I think there's some validity to the main master seal leaking, but not being completely shot as to not work. When full power force without the bike running the lever pulls to a gritty feeling stop and -very- slowly compresses to the bar. I will check when the kit comes in for any signs of defects in the cylinder bore before reassembly I will also replace the crush washers on the banjo because that is cheap insurance. Thanks to everyone who replied, I'll be posting back in a week or so to let anyone interested in my results and try to document anything I find that may or may not be what I'm expecting to find as the problem.
 

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<< snip >> I bleed the furthest caliper first, new bottle dot 4 every time. Close off bleed nipple and rise with distilled water. Next the closer caliper, same procedure, last bleed the master cylinder .

For what it is worth, the Service Manual says to bleed the master cylinder first, then the calipers.
 

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Good catch.

The reason for bleeding the master cylinder first is in case there is air bubbles in the line, it will naturally migrate to the highest spot, which is neat the master cylinder. If you start bleeding at the calipers, you risk pushing the bubbles down towards the manifold and maybe the ABS module, but you may not be able to push them all the way down and out of the caliper nipples. Over time, the bubble may just slowly return back up the highest spot again.
 

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I decided to buy a rebuild kit from all balls racing for around 24$ I think there's some validity to the main master seal leaking, but not being completely shot as to not work. When full power force without the bike running the lever pulls to a gritty feeling stop and -very- slowly compresses to the bar. I will check when the kit comes in for any signs of defects in the cylinder bore before reassembly I will also replace the crush washers on the banjo because that is cheap insurance. Thanks to everyone who replied, I'll be posting back in a week or so to let anyone interested in my results and try to document anything I find that may or may not be what I'm expecting to find as the problem.
Thats about all you can do. Im anxious to see if it really fixes it. I should have spent some time on mine. I suppose the factory could have a defective seal, or maybe they damaged it during assembly. I know you know this, but those seals are easy to deal with when they are coated in brake fluid.
 

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Discussion Starter #15
So with the world being in the state it is, I have found some free time to begin the process of replacing the seals and while I'm at it I will replace the fluid reservoir. I picked up the all balls seal set for about 24$ and it arrived in five days. Began by removing the brake lever, broke the banjo loose with a towel to catch any fluid, removed the brake light sensor and removed the master from the bars. Disconnected the brake line and zip tied the open end into a plastic bottle and taped it off so that fluid wont ruin everything. Removed the reservoir, and completely drained all fluid. I pulled the boot back in the cylinder and it was a colossal mess of white corrosion and rust. I am attaching pics of the mess. I cleaned it up with a dremel wheel and replaced the seals on the piston. I will pack the ball joint with with moly grease behing the seal when I reassemble tomorrow.. I'm 100% certain there was a small leak in those piston seals. There was also crud (dirt) in between the seal and body of the piston that sits closest to the lever. So I will follow up when I'm done in the next day or two. Thanks to everone for the help and replies.
 

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I would throw that one away. It's not worth rebuilding. The master cylinder from a 2009-2015 zx10 is a direct swap. That should not be much more than a rebuild kit, from ebay. I would not risk the rest of the system in rebuilding that one.

That looks like water damage from pressure washing.
 

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That's a 2016?! I've opened up 10+yr old master cylinders that look way cleaner than that.
 
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I dont remember where you are at. If you are here in the usa, I have a spare master cylinder from something...should be the correct size as I didnt buy anything that was not compatible with he **** i was already hoarding . I'm not looking to get rich. May trade for toilet paper (new).
 

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Discussion Starter #19
Never pressure washed it. I do commute daily in all conditions (no snow or salt) and it has seen a ton of rain. I'm in Florida but away from salt water in Tallahassee. I think the seals failed and the boot on the shaft held the brake fluid and since the fluid is hygroscopic absorbed water so it had the white corrosion and rusted the piston ball joint.
 

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I bought a ten year old suzuki dr350. It was a service bike , on a dairy farm. Its master cylinder was cleaner than that one.

Did the rebuild kit fix it? Did it hold overnight?
 
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