Front brakes spongy - please read - Kawasaki Ninja 1000 Forum
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post #1 of 21 Old 02-20-2020, 03:49 PM Thread Starter
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Front brakes spongy - please read

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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post #2 of 21 Old 02-20-2020, 04:09 PM
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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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post #3 of 21 Old 02-20-2020, 04:13 PM
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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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post #4 of 21 Old 02-20-2020, 07:43 PM Thread Starter
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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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post #5 of 21 Old 02-20-2020, 08:31 PM
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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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post #6 of 21 Old 02-20-2020, 11:53 PM Thread Starter
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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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post #7 of 21 Old 02-21-2020, 01:02 AM
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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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post #8 of 21 Old 02-21-2020, 08:34 AM
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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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post #9 of 21 Old 02-21-2020, 10:49 AM
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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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post #10 of 21 Old 02-21-2020, 12:33 PM
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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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