brake fade - Page 5 - Kawasaki ZX-10R.net
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post #41 of 112 Old 02-17-2007, 02:59 PM
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The problem I see with your theory is that firstly brake fluid has a very low expansion rate due to its molecular makeup and also the reservoir is large enough to cope with any expansion and secondly air bubbles will always get to the top eventually, so the air will always end up in the master.

There arent many places for air to get trapped apart from the cross over tube on a stock system , there are a few nooks in the calipers but nothing that a good ride wouldnt solve .

One thing I dont condone is pressure bleeding and it is bad practice in my industry, this causes a lot of air compression and when released the bubbles tend to divide whilst trying to escape under pressure , its okay to start a bleed, but you must do a proper bleed after to release the remaining bubbles.
This is why I am not particularly keen on vacuum bleeding as the initial rush of fluid breaks up the larger bubbles into froth, I am sure you have seen this when you crack the bleeder under vacuum.

As for the bite being at different intervals with different thickness pads , I would expect it to be the same initially but different as the pads heated up.

Its a bit of a black art really and there are so many variables to consider, its not very often a true source is found for braking anomolies apart from the obvious mechanical attributes ,it could be line diameter, heat , pad material , master cylinder size and many other things including the cap on the reservoir.
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post #42 of 112 Old 02-17-2007, 03:22 PM
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I just had one of my brain farts , are you using a billet reservoir cap ?

If so then check to see if it has a ridge machined on its inner face, I have had this problem before on customer bikes where they have replaced the caps with blingy ones with no vent system, they remove the nylon spacer on top of the diaphragm (it has 3 grooves in it to vent the reservoir) , this causes a vacuum when the pads wear and will retract the pistons in the caliper.

Just food for thought.
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post #43 of 112 Old 02-17-2007, 04:21 PM
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Another point to consider. The fluid volume pushed by the m/c is rather small. As the calipers heat, ala track conditions, they expand (ever heat aluminum for a bearing replacement?), increasing their volume, and requiring more lever movement for equivalent braking . I believe this is why you'll notice brake adjusters are common on race bikes, and why your brakes seem to come back when they cool. This would seem to partially explain the condition getting worse with worn pads. With worn pads the pistons are partially extended, increasing the size of the volume that is expanded by the heating of the caliper.

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post #44 of 112 Old 02-17-2007, 06:21 PM
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Feasible , but I would think you would need a fair few laps to keep the heat up.
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post #45 of 112 Old 02-17-2007, 09:46 PM
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A couple of points. 1) The amount of air in the system when you button up the system = the amount of air in the system when you arrive at the track = the amount of air in the system after 20 hard laps. Unless you have some serious leaks, the amount of air won't change. The size of the air bubbles may change. Lower pressure/vacuum equals bigger bubbles. Higher temperature means bigger bubbles. 2) I don't believe you can get enough thermal expansion of the calipers to make a difference. Remember, even if the total system volume increases by some tiny amount, every actuation of the brakes will add a small volume of fluid to compensate. That's the way the reservoir works. What no one has explained yet: if I'm out on the track putting huge amounts of heat into my brakes until the fluid boils behind the pistons (that's one type of fade), giving me a gas bubble behind each piston, how does pushing on those bubbles with a different m/c solve the problem?
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post #46 of 112 Old 02-17-2007, 11:13 PM
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Quote:
Originally Posted by 12RPilot
I may as well jump in and open this can of worms right now. There are two things that will cause brake fade. One is the effects of heat on the rotor and pads that cause your coefficient of friction to decrease. This is usually from gases migrating out of the pads and keeping the friction low between the rotor and pads. You can squeeze the lever really hard with little braking taking place. This type of fade doesn't make your lever travel change.
The other type of fade occurs when you get gases in the fluid. This can be from poor bleeding (air) or boiling fluid. Brake fluid won't compress, gases will. This type of fade makes your lever travel farther for a given brake pressure. Eventually, the lever can contact the grip if enough gas builds up. Obviously, the fluid boils in the caliper, behind the pistons, where the heat is. It doesn't matter what you are using to push on that gas bubble, it will be mushy until the fluid cools and the gas condenses back to a fluid. So changing your master cylinder to fix a problem with brake fade is chasing ghosts. Concentrate on the root of the problem first. Just my .02......
I thought I would quote 12rpilot on this so you can read his words again. He is right on point here. I am sure radial pumps are cool and I wouldn't mind having one myself, but I get to play with 2 differant '04 ZX10's and both have the stock M/C and both have rock solid brakes. For one thing, I can't get a good bleed (no air) with any vacuum pump system. They are great for pumping a lot of fluid through when you have new brake lines or a new m/c. But beyond that, I don't use them for the final bleed. Maybe the reason you guys got a big improvement with radial m/c's is that you got a better bleed job this time.

Don't confuse me with facts, my mind is already made up.
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post #47 of 112 Old 02-18-2007, 05:34 AM
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Quote:
Originally Posted by 12RPilot
A couple of points. 1) The amount of air in the system when you button up the system = the amount of air in the system when you arrive at the track = the amount of air in the system after 20 hard laps. Unless you have some serious leaks, the amount of air won't change. The size of the air bubbles may change. Lower pressure/vacuum equals bigger bubbles. Higher temperature means bigger bubbles. 2) I don't believe you can get enough thermal expansion of the calipers to make a difference. Remember, even if the total system volume increases by some tiny amount, every actuation of the brakes will add a small volume of fluid to compensate. That's the way the reservoir works. What no one has explained yet: if I'm out on the track putting huge amounts of heat into my brakes until the fluid boils behind the pistons (that's one type of fade), giving me a gas bubble behind each piston, how does pushing on those bubbles with a different m/c solve the problem?
for one its quite possible the fluid gets hot enough to cause the MC to have lever fade even though its farthest away from the heat source if in fact the MC internal makeup is suspect (and we know the OEM MC is)
in the case of the zx6r radial it has a 16mm piston vs the OEM having a 14mm so this is an all around plus. as for the Brembo it has an 18mm piston so again its a step in a positive direction with a quality component that has proven superior to OEM components and has all but removed the renowned lever fade when the system gets abused repeatedly.

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post #48 of 112 Old 02-18-2007, 05:56 AM
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Guys,

I will give you some real life feed back.

1) Track day at Phillip Island, stock 06 10r, after 5 laps i had to come in as the lever was coming back to the bar.
2) Track day with SS lines HH, race pads and race fluid. This achieved good solid braking but with some fade after 6-10 laps
2) Track day with the above but Brembo MC and 40 degree day. No fade after repeated hot laps.

This is all i can report and its fact, all done at Phillip Island in a three week period.

SS lines, race pads and the MC works !

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post #49 of 112 Old 02-18-2007, 08:54 AM
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Hmmmm. m/c getting hot from heavy usage. I have never checked mine, but I would think when you come in from a really hard brake usage session that you will not be able to feel any significant amount of heat in the m/c. I don't know, but it just seems logical to me. Now the calipers would be another story. I am just thinking about all of the components that are a fairly long way from the heat source and the only way for that heat to be translated to the m/c is through the brake fluid. And those brake lines have a lot of cold air blowing around them. And relatively speaking, the brake fluid has so little mass in comparison to the brake lines. It seems like little or no heat could find its way to the m/c. I hope I will remember to check mine the next time I ride vigorously.

And BTW, in a perfect world, a m/c with a larger piston will require more effort (at the lever, if the lever ratio is the same) to create the same psi in the system as a m/c with a smaller piston.

Don't confuse me with facts, my mind is already made up.
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post #50 of 112 Old 02-18-2007, 09:35 AM
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Zeta you are correct different size cylinder bores will give you a different feel and change the mechanical advantage , when the system is prime you are still only moving the same amount of fluid to move the pads and changing the amount of force to do it with different cylinder volumes.
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