Master Cylinder Air Leak, Bleed nipple seal - ZX6R Forum
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post #1 of 17 Old 07-08-2015, 09:42 PM Thread Starter
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Master Cylinder Air Leak, Bleed nipple seal

How common is it for brake bleed nipples to seal incorrectly? Does anyone use some type of sealant for the brake bleeders?

I bought new braided lines for my 2014 zx6r and once at the track noticed the lever was getting soft little by little. I saw brake fluid was seeping from the master cylinder bleed nipple and took it off, cleaned it with brake cleaner and thought that would be that. As I bleed the brakes I notice that brake lever pressure is there and then, suddenly, air gets into the line. I continue to bleed the brakes, feel that there is pressure there and once again, suddenly, air gets into the line.

I took apart the bleed nipples from the calipers and noticed those had some thread sealant which prevents the fluid from seeping unlike the one from the master cylinder. I replaced the crush washers from the banjos just to be safe and I am waiting on new speed bleeders to replace the stock ones with and some speed bleeder thread sealant. If that doesn't work I think I'll just get a brembo rcs master because I am not risking brake failure.

Anyone else had this type of problem with the stock Nissin master cylinder?

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Last edited by jd41; 02-11-2017 at 10:13 PM.
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post #2 of 17 Old 07-08-2015, 09:48 PM
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Edit: Nevermind below. I fired this off too quickly.

====

Speed bleeders have a coating on them that help with the seal and they recommend re-applying if you bleed a lot. They sell a little bottle with applicator.

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post #3 of 17 Old 07-08-2015, 10:52 PM Thread Starter
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Originally Posted by jimundascore View Post
Edit: Nevermind below. I fired this off too quickly.

====

Speed bleeders have a coating on them that help with the seal and they recommend re-applying if you bleed a lot. They sell a little bottle with applicator.

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Thank you for the comment, but I was wondering how many people out there have encountered this problem and how they were able to resolve it. I saw some posts of riders using teflon (PTFE) tape and such but how common is this really?

It is somewhat frustrating to have this problem on a new bike.
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post #4 of 17 Old 07-08-2015, 11:11 PM
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Sorry, I can't tell you I've run into this. The best I can do, and possibly the cheapest option for you is to look at the link below. Love those guys for easy bleeding.

i've had seepage from the master cylinder, but only because I was a dispshit and didn't tighten it enough. Air seepage between the brass washers.

In-between steps, if you think you have this solved, make sure to put a zip tie on your brake lever, leave it over night and see what you have bled in the morning. I recommend that if you think you have a bleeding problem or not. Standard practice.

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Sealant
Used to replace the thread sealant that will eventually wear off if you bleeded your brakes frequently. It is mainly used by racers who bleed their brakes after every race. It comes in a 1/2 ounce bottle with an applicator brush built in to the cap. $10.00
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post #5 of 17 Old 07-09-2015, 09:26 AM Thread Starter
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I'll give the sealant a try. It almost felt like the stock MC bleeder wasn't the right size.
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post #6 of 17 Old 07-09-2015, 10:43 AM
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Mine seals correctly when closed but not at the threads so I can't bleed it with a vacuum bleeder. It sounds as though I am a little better off than you but now you know you aren't the only one with master cylinder bleeder issues. I tried sealing the threads but it still wasn't perfect. I didn't feel like messing with it more at the time. Luckily, the master is the easiest one to bleed manually so I just do that one that way.
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post #7 of 17 Old 07-09-2015, 10:58 AM Thread Starter
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If the sealant and new bleed nipples don't fix it I have an "excuse" to buy a brembo MC , although I would rather avoid the cost . Brakes are the most important components of a motorcycle, at least this is the order I would rate their importance: 1 brakes, 2 tires, 3 suspension, 4 everything else.
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post #8 of 17 Old 07-09-2015, 12:30 PM
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Brake bleed screws use a mechanical seal where the tapered end fits in a matching female end inside the port. The threads should not leak at all when the screw is torqued down as the mechanical seal cuts off any pressure from reaching the threads. The threads can leak when open as the thread fit is typically a bit loose. If its leaking through the nipple, then the seal is not seating properly. I would remove the screw and make sure there is no debris trapped on the sealing surface and inspect for damage to both surfaces. If its dirty, clean it off and try it again. If its damaged, it may require replacement of the screw, the cylinder, or both.

Thread sealant should not be used. Some bleed screws do have it, but its only to prevent fluid from moving past the threads during the bleed process. Trying to fix a leak of the mechanical seal with tape on the threads is a band-aid and probably not going to seal properly long term. Thread tape is typically used on tapered threads (NPT, BPT) which become tighter as you screw it in more. If you want to put sealant on the threads, I would avoid any kind of thread tape. They tend to tear as you screw it in and with bleed screws in particular, the tape would probably get shredded up as you loosen and tighten the screw during a bleed. Most liquid sealants will likely be designed to be torqued down wet and will dry in place. Since a bleed screw is designed to be open and closed several times during a bleed procedure, it would likely become useless as it may not reseal correctly. There are thread seals you apply to one side and let dry that are reusable to a degree. Not sure if this stuff is easy to find in stores or not. Unless you are vacuum bleeding, I wouldn't bother with it.
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post #9 of 17 Old 07-09-2015, 01:08 PM Thread Starter
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Speed Bleeder Thread Sealant - Sport Bike Track Gear



This seems to be designed for sealing the brake bleeder threads and either way the bleeders are being replaced. If it doesn't work I'll just buy a new MC. My main concern is not knowing if this happens to others MC's. Maybe I got one of the bad ones.
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post #10 of 17 Old 07-09-2015, 02:08 PM
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Are you only concerned with the air seeping past the threads while bleeding? If so, that may help. I've used wheel bearing grease around the bleed screw to do the same thing before. Its easy to get (I always have some) and you can apply it without removing the bleed screw as you just put some in the crack between the bleed screw and the port. Its messy and is definitely not a long term solution, but is a quick solution for preventing air from getting sucked in around the threads. Just clean it up when done. Neither is a good solution if your not getting a good seal with the bleed screw closed as that means the port through the bleed screw is open to the fluid in the system.
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post #11 of 17 Old 07-09-2015, 02:14 PM Thread Starter
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Originally Posted by CKwik240 View Post
Are you only concerned with the air seeping past the threads while bleeding? If so, that may help. I've used wheel bearing grease around the bleed screw to do the same thing before. Its easy to get (I always have some) and you can apply it without removing the bleed screw as you just put some in the crack between the bleed screw and the port. Its messy and is definitely not a long term solution, but is a quick solution for preventing air from getting sucked in around the threads. Just clean it up when done. Neither is a good solution if your not getting a good seal with the bleed screw closed as that means the port through the bleed screw is open to the fluid in the system.
While bleeding brake fluid seeps through, the problem is even after I close it, it keeps doing it and I'm thinking air is getting in too. I've even torqued it to spec, I think 69in-lb, to make sure.
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post #12 of 17 Old 07-09-2015, 04:20 PM
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You need to fix the problem at the mechanical seal. So long as this is a problem, the fluid can escape through the hole at the top of the bleed screw and even draw air through it. Sealing the threads will not fix this problem unless its a speed bleeder in which case there is a check valve to prevent a backflow of air. It can still leak fluid though. Inspect the tapered part on the end of the screw and the matched female end inside the port. Clean out any debris and try again. If you see damage to either, you may need to replace them. These types of connections use the elastic deformations of the metals to seal and requires a good deal of precision in the mating surfaces. Moreso in higher pressure connections. Also inspect for any cracks in the screw and MC.
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post #13 of 17 Old 07-09-2015, 11:30 PM
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the stock nissin master on my track bike was bleeding air into it over a 2 week period. I replaced it with a brembo rcs just because it gave me the excuse to, then pulled it apart, cleaned it (there was more dirty gunk in there than I expected), resealed it, tested it, and sold it.

75,000km's + first year of track and still going strong
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post #14 of 17 Old 07-09-2015, 11:50 PM
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Quote:
Originally Posted by jd41 View Post
How common is it for brake bleed nipples to seal incorrectly? Does anyone use some type of sealant for the brake bleeders?

I bought new braided lines for my 2014 zx6r and once at the track noticed the lever was getting soft little by little. I saw brake fluid was seeping from the master cylinder bleed nipple and took it off, cleaned it with brake cleaner and thought that would be that. As I bleed the brakes I notice that brake lever pressure is there and then, suddenly, air gets into the line. I continue to bleed the brakes, feel that there is pressure there and once again, suddenly, air gets into the line.

I took apart the bleed nipples from the calipers and noticed those had some thread sealant which prevents the fluid from seeping unlike the one from the master cylinder. I replaced the crush washers from the banjos just to be safe and I am waiting on new speed bleeders to replace the stock ones with and some speed bleeder thread sealant. If that doesn't work I think I'll just get a brembo rcs master because I am not risking brake failure.

Anyone else had this type of problem with the stock Nissin master cylinder?

Attachment 35133

Attachment 35131

Attachment 35132
Buy a rebuild kit. Prob dirt preventing seat of bleeder mating with MC side of things.

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post #15 of 17 Old 07-10-2015, 08:19 AM Thread Starter
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Quote:
Originally Posted by ymad4 View Post
the stock nissin master on my track bike was bleeding air into it over a 2 week period. I replaced it with a brembo rcs just because it gave me the excuse to, then pulled it apart, cleaned it (there was more dirty gunk in there than I expected), resealed it, tested it, and sold it.
I wanted to avoid rebuilding it since it's practically brand new. I was thinking the exact same thing as this guy though, "excuse" to buy a new brembo. Although I would much rather spend that money on more track days.

Last edited by jd41; 07-10-2015 at 09:15 AM.
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