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Discussion Starter #1
I decided to change my brake fluid today using my vacuum bleeder. Rear brake went well but I got a big surprise on the front. After a little fluid came out I got a huge air bubble.
My front brake always felt mushy but it's the only 300 I've ridden and lots of people say the front brake isn't that great. Its a 2017 and I got it with 3000 miles so I didn't suspect air in the system.
Since getting rid of the air the front brake is, as you'd expect, incredibly better.
There are only three possibilities I can think of
It was bled improperly before. I doubt this because the bleeder and cap both looked untouched and the fluid was old.
It was dumped on its side and air got in that way. I doubt this as well as the bike has 0 evidence of ever being down.
And finally the one I bet is that case. It's been like that since new. I find this particularly annoying as this is the only used bike I've ever bought at a dealership and the tech who has probably ridden a hundred 300s should have noticed.

Ah well. Anyway, bleed those brakes. Who knows a better braking system may be hiding in there for you too!
 

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I would have to rate the front brake on my 300 as EXCELLENT. Not mushy at all and I feel perfectly confident that it will stop me in any braking situation.

The rear brake is a different story, as everybody knows. It works, but not even close to the stopping performance of the front brake.
 

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I decided to change my brake fluid today using my vacuum bleeder. Rear brake went well but I got a big surprise on the front. After a little fluid came out I got a huge air bubble.
My front brake always felt mushy but it's the only 300 I've ridden and lots of people say the front brake isn't that great. Its a 2017 and I got it with 3000 miles so I didn't suspect air in the system.
Since getting rid of the air the front brake is, as you'd expect, incredibly better.
There are only three possibilities I can think of
It was bled improperly before. I doubt this because the bleeder and cap both looked untouched and the fluid was old.
It was dumped on its side and air got in that way. I doubt this as well as the bike has 0 evidence of ever being down.
And finally the one I bet is that case. It's been like that since new. I find this particularly annoying as this is the only used bike I've ever bought at a dealership and the tech who has probably ridden a hundred 300s should have noticed.

Ah well. Anyway, bleed those brakes. Who knows a better braking system may be hiding in there for you too!
If nothing appears to have been wrenched, then I would opt for the ............ been like that since new.

As we all know, no company or employee is perfect. :surprise:

When I took delivery of my Fiat 124 Spider, it rode very hard. " I " checked the tires and found all 4 to have 50 pounds of air pressure. Now, how does that happen with 30 PSI tires. :WTF:
 

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I feel the front brake works ok...but the feel is crap...soft and spongey. I have bled and fully replaced the fluid twice..made no difference. Rubber banded the lever down and left for 24 hours...no difference. I haven’t vacuum bled them (although I have a mighty vac...) and I’ve also considered reverse bleeding, as some online have suggested that as a fix for our spongey brakes.

I probably wouldn’t notice how bad they are but I also have a Kymco scooter and that has a front disc with a very nice, solid feel....much better than the Ninja.
 

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Discussion Starter #6
I will say that motorcycle brakes can be notoriously hard to bleed conventionally. I've had bikes where the only way I could bleed them the normal way was to remove the caliper and hold it above the master cylinder.

My vacuum bleeder runs off my air compressor and draws the fluid fast enough that it pulls the air bubbles with it giving them little chance to get stuck.

My front brake used to feel like you're describing yours. Now it's like a whole new braking system. Of course it's not going to compare to a big boy brake system but unlike before it feels perfectly adequate now. My brake feel has gone from mushy and 0 feedback to nice and firm. I used to be able to pull the lever almost all the way to the grip. Now it doesn't get close.
 

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Just wanted to add that the front brake on my 300 works fantastically. :yahoo:

Probably one of the best front brakes that I have ever experienced on all of the bikes that I have ever owned. When using it, I know for a fact with just a little pressure applied to the lever, I will be slowing or stopping. :emot-thumbsup:

Their is no pulling hard or pulling the lever to the grip. :smile2:
 

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I will say that motorcycle brakes can be notoriously hard to bleed conventionally. I've had bikes where the only way I could bleed them the normal way was to remove the caliper and hold it above the master cylinder.

My vacuum bleeder runs off my air compressor and draws the fluid fast enough that it pulls the air bubbles with it giving them little chance to get stuck.

My front brake used to feel like you're describing yours. Now it's like a whole new braking system. Of course it's not going to compare to a big boy brake system but unlike before it feels perfectly adequate now. My brake feel has gone from mushy and 0 feedback to nice and firm. I used to be able to pull the lever almost all the way to the grip. Now it doesn't get close.
Does your bike have ABS?

Did you leave the ABS module (if applicable) and calipers mounted when you vacuum bled your brakes?

My 2015 Ninja 300 ABS has a spongy front brake and I have access to a good shop air compressor, wondering if I should buy a vacuum bleeder and have a go at it. I'm due for a brake fluid change too.
 

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Discussion Starter #10
Yes ABS and yes I left everything in place. The air powered vacuum bleeder draws the fluid fast enough that air bubbles almost always get drawn along with it and don't have time to resettle wherever they are trapped. My vacuum bleeder will empty the reservoir in about 3 seconds. I turn it on and just keep a steady stream of fresh fluid going back into the reservoir.
They aren't super cheap (I'm a mechanic so I already had it) but once you've used one it's hard to go back to the old way of bleeding brakes. They are also awesome for sucking fluids out of reservoirs etc.
 

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Which model vacuum bleeder do you have?

When I bought my bike (2016 ABS) the front lever was also super mushy. I rode like that for almost 2 years since I didn't know that there was air in the lines (two annual state inspections said nothing about it and it was my first bike). I gravity bled the front brake with fresh fluid and it got very firm. Then after a few weeks it got soft again (but nowhere near as soft as it once was). I think I might have accidentally got the ABS system to pulsate during that time (went to the track), and maybe some air stuck in the ABS pump re-entered the system (??). I was looking into alternative bleeding methods to help get all the air out, but vacuum bleeder reviews on Amazon led me to believe it's more of an optional convenience.
 

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Discussion Starter #12
Mine is a Capri brand. I got it off Amazon I think. In automotive applications is a "nice to have" but many motorcycles are much harder to bleed (probably because of the much more vertical lines) and for those I call it a necessity.
As a mechanic it's a must for me in automotive as well because flushing a brake system takes forever without it and requires 2 ppl.
 

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When I tried to use a vacuum bleeder, I believe it was sucking air at the nipple. I was amazed at how much air was coming out. its not possible for that much air to have been in such a small line. I squeeze with the nipple closed, open the nipple, then close it again before releasing the brake. Any small bubbles get pulled out by the master cylinder when the brake is released. Braided lines help a little.
 

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Discussion Starter #14 (Edited)
It depends on the caliper. Some have a bleeder that fits the threads tightly enough to not leak are past but some do. On the ones that do I just remove the bleeder completely and hold the vacuum adapter directly against the caliper. It will form a good seal that way.

The squeeze, open, close and release method is not always effective on motorcycle brakes. As i stated before because of the way they are designed sometimes you can bleed that way for hours and still not get all the air out of the system. Shops will sometimes have bench bleeding rigs to overcome this but I've found the vacuum bleeder has worked for me every time (so far anyway)
 

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Another technique that I have had success was to pump the brake to extend the piston at the caliper (not all the way out). Then manually push the piston back into the caliper, thereby forcing any air bubbles in the line, back up to the reservoir.
 
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