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So, I have a Hayes Stroker Trail brakes, and they stop well, but the don't feel as firm as I would like when applying pressure to the lever. The guy at my LBS suggested doing what he called "charging up the brakes", which he said was applying extra pressure into the system when bleeding. From what I understood, I think he meant that after finishing the bleed apply an extra amount of pressure right before closing up the master cylinder bolt. Is this true? Will this make my levers feel firmer?
 

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that is not physically possible. hydraulic fluid does not compress so any pressure increase in the system will present itself at the pistons as extension. basically, if you try to "pressurize" the system, it will just extend the pistons and your pads will potentially rub the rotor.

if they aren't very firm, try bleeding the brakes to remove air, and/or adjust the lever throw (if possible). you can also try installing new pads with a more aggressive pad compound. even with the same compound, new pads can have the effect of increasing lever stiffness because the new pad width will take up a lot of the gap between the pads and rotor.
 

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Soft levers mean that there is something compressing/flexing. Most of the time this means there is air in your lines-- this is fixed with a good bleed. Next try adjusting your lever outward, sometimes this changes the perceived firmness of your lever. After that, the next culprit is hose flex depending on how long your hoses are and what they are made of. You can upgrade to better hoses which will usually give you a firmer lever feel--my advice is that this is way more of a PIA then it's usually worth, and if your brakes are capable of stopping you effectively, then you it's probably in your best interest to just get used to it.
 

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slidecontrol said:
sounds like the LBS guy is taking about "overfilling" the brakes.
fluid level doesn't make a difference, as long as it's greater than the allowed minimum. you could put a 10gal master cylinder reservoir on your lever and fill it to the brim, and it still won't make your brakes any more powerful.
 

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The guy at my LBS suggested doing what he called "charging up the brakes", which he said was applying extra pressure into the system when bleeding.
Keep your bike and its brakes away from this person. Poor lever feel, assuming it's not mechanical flex, is caused by either air in the line or incorrect caliper/disc alignment. As Alex explained, it's just not possible to have any pressure at all in a brake system without having it close the pistons.
 

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Let me take a stab at this. With an open system you have a rubber diaphragm inside the reservoir. You can ( and I have ) introduce an additional small amount of fluid after filling the brake and reinstalling the cover to tighten up the system. If you push the syringe at the end of the filling ( after the cover is tight ) until you feel a substantial resistance you are overfilling or over charging the brake. This does two things.

1) It will push the rubber boot back ( air is compressible ) which allows a little more fluid into the system. The compressed air behind the diaphragm acts as an assist spring imo to increase sensitivity of the levers.

2) It will push the pistons out.

If you overfill too much the pads will be too tight. Under fill and although there's no air in the system the pistons will travel too far before the pads bite.....at least this is true for my brakes which are an open system. When you take out the syringe fluid will be pouring out of the hole so your going to lose some fluid no matter how quick you are. By exerting extra pressure on the syringe even with a slight loss in fluid your brake will still be very slightly overfilled which to me means it's been charged if you will. I've experimented with my Gustav's. I can tune the feel by the amount of overfill.

I think the guy at your LBS knows what he's talking about.
 

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I think the guy at your LBS knows what he's talking about.
There is no pressure (beyond normal atmospheric) within in a hydraulic system until the lever is pulled. If the fluid (or air) in the system is somehow pressurised, by even the tiniest amount, then the result is that the pistons will extend. The diaphragm is outside of the compression portion of the system and has no impact whatsoever on the feel/operation of the lever.

Overfilling the system has no benefits to an open system. The MC has to be topped off in order to prevent trapped air from getting past the lever's piston seal. It's possible and simple to manipulate the pistons in order to minimise the gap between the pads and the disc. Overfilling the system in order to achieve the same is pointless and is only going to increase the probability of performance problems when the fluid starts to expand (from heating) during use. Because the system is beyond capacity, the expanding fluid is either going to blow past the diaphragm when the lever is released or it's going to push the pistons further out. The path of least resistance is the pistons, so the result will be that the lever travel is then reduced further. It's not an issue on all brakes, obviously, but there's no point, in my opinion, introducing a possibility for braking problems when another solution is available (and was intended in the design of the component).
 

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In my experience a very small amount of fluid makes all the difference in the world. I push the syringe as hard as I can after the cover screws are tight, then watch the pressure / volume coming out after I unscrew the tube. For me it's in the timing. I wait until the pressure /volume appears slightly above atmospheric.

Initially overfilling gives me time to get the plug tight at the exact moment I want. It's simply trial and error. My method may not work for all, but it words for me, and see no reason it wouldn't work for others. Not worried about the fluid heating up. The system was designed for that. Again, we're talking about a very small amount of fluid.That's what tweaking is about. God's in the details..

What's actually happening when you top off the system is the pistons are expanding against the pads. If you were to jam as much fluid in as you could the wheel probably wouldn't turn, so you watch the fill port and get the bolt in when some of the excess fluid comes out trying to get to a condition where the system has just a little more fluid which makes all the difference in the world with responsiveness imo at least with my brakes. You may not see a tangible advantage in tweaking the fluid volume, but I do with my Gustav's
 

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suba said:
In my experience a very small amount of fluid makes all the difference in the world. I push the syringe as hard as I can after the cover screws are tight, then watch the pressure / volume coming out after I unscrew the tube. For me it's in the timing. I wait until the pressure /volume appears slightly above atmospheric.

Initially overfilling gives me time to get the plug tight at the exact moment I want. It's simply trial and error. My method may not work for all, but it words for me, and see no reason it wouldn't work for others. Not worried about the fluid heating up. The system was designed for that. Again, we're talking about a very small amount of fluid.That's what tweaking is about. God's in the details..

What's actually happening when you top off the system is the pistons are expanding against the pads. If you were to jam as much fluid in as you could the wheel probably wouldn't turn, so you watch the fill port and get the bolt in when some of the excess fluid comes out trying to get to a condition where the system has just a little more fluid which makes all the difference in the world with responsiveness imo at least with my brakes. You may not see a tangible advantage in tweaking the fluid volume, but I do with my Gustav's
Whether you extend the pistons with pressure from a syringe, or extend the pistons with the brake lever, all you're doing is making the overall volume of the system larger (by increasing the distance between the back of the piston(s) and the front lever piston seal) and filling it up with fluid. Just because you believe the fluid to be pressurised, doesn't mean that it actually is; and I assure you that it is not.

You're overfilling the system to create a smaller distance between the pads and the disc. It's that simple. This smaller distance can be achieved by manually manipulating the pistons, which results in the same effect in feel at the lever but without introducing the increased risk of reduced performance from fluid expansion by eliminating the diaphragm's ability to expand with the fluid.
 

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Fair enough. The op should have omitted the term pressurized I think. That is not the right term. If I said pressurized I retract it. We are talking volume. I do know I cannot in any way that I know of reduce the distance between my pistons and pads unless I top off more fluid. I am talking a very very small amount. If I don't do this the levers will move too far before biting. There's no lever adjustment to compensate.

Thanks for taking the time to reply. I gotta run....
 

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Discussion Starter · #12 ·
SteveUK said:
You're overfilling the system to create a smaller distance between the pads and the disc. It's that simple. This smaller distance can be achieved by manually manipulating the pistons, which results in the same effect in feel at the lever but without introducing the increased risk of reduced performance from fluid expansion by eliminating the diaphragm's ability to expand with the fluid.
Yeah I gues that's what the guy meant add a litle extra volume of fluid into the MC, thanks Steve. By the way how exactly does one go about manually manipulating the pistons?
 

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take the wheel out, and give the lever a pull [ not all the way ] . with out a disc the pistons will overtravel slightly. replace the wheel and see if you like the new pad clearance.
still too much lever travel, repeat the process til you're happy
if its too tight, push the pads back and try again,
 

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Doing what the mechanic was doing is incorrect, stupid, and can cause serious issues. Basically, he's making it a closed system instead of an open one, in order to position the pads slightly closer to the rotor. Try using it that way on a long descent, and your brakes will lock from the fluid heating up, and having no where to expand to. There's a reason we left closed systems behind 15 years ago! Seriously, don't ever let that mechanic work on your bike again.
 

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bad mechanic said:
Doing what the mechanic was doing is incorrect, stupid, and can cause serious issues. Basically, he's making it a closed system instead of an open one, in order to position the pads slightly closer to the rotor. Try using it that way on a long descent, and your brakes will lock from the fluid heating up, and having no where to expand to. There's a reason we left closed systems behind 15 years ago! Seriously, don't ever let that mechanic work on your bike again.
I think you're taking this to an extreme. Can you site one example of someone who's brakes failed on a long decent which can be directly attributed to overfilling an open system ? If you can't get the rotors between the pads you've got too much fluid so bleed some because your not riding till you do. If your rotors are running without drag, and the modulation is there you've got the right amount of fluid. If you have no drag, but unresponsive levers add some fluid. If you don't squeeze the syringe hard enough just before the bolt goes in your probably not getting the right amount in, because a little will leak out before the bolt is tight. At least that's what happens to me. It takes a miniscule amount to go from just right to too tight. Easier to bleed a little to get them tweaked right than have to open up the system and add more fluid imo. Open systems have build safety. Closed systems operate on an entirely different principle.
 

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bad mechanic said:
Doing what the mechanic was doing is incorrect, stupid, and can cause serious issues. Basically, he's making it a closed system instead of an open one, in order to position the pads slightly closer to the rotor. Try using it that way on a long descent, and your brakes will lock from the fluid heating up, and having no where to expand to. There's a reason we left closed systems behind 15 years ago! Seriously, don't ever let that mechanic work on your bike again.
brake fluid does not appreciably expand when it heats up. that is what makes it brake fluid, and not simply hydraulic fluid.

what an ironic screen name.
 

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alexrex20 said:
brake fluid does not appreciably expand when it heats up. that is what makes it brake fluid, and not simply hydraulic fluid.
You're wrong, but thanks for trying. Brake fluid IS a hydraulic fluid, and it's key features are non-compressibility and high boiling point. It will however expand from heat, and if it's absorbed any water (it's hydrophilic, remember?) then it will expand even more. In a closed system, it doesn't need to expand a lot either to start causing problems. Here you go, it's under the "Too much is bad" heading:
http://www.prenhall.com/autoweb/techtips/brakes.html

Know something else? I've personally experienced brakes locking from heat, way back in the day.

alexrex20 said:
what an ironic screen name.
Oh, the irony.
 

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suba said:
I think you're taking this to an extreme. Can you site one example of someone who's brakes failed on a long decent which can be directly attributed to overfilling an open system ? If you can't get the rotors between the pads you've got too much fluid so bleed some because your not riding till you do. If your rotors are running without drag, and the modulation is there you've got the right amount of fluid. If you have no drag, but unresponsive levers add some fluid. If you don't squeeze the syringe hard enough just before the bolt goes in your probably not getting the right amount in, because a little will leak out before the bolt is tight. At least that's what happens to me. It takes a miniscule amount to go from just right to too tight. Easier to bleed a little to get them tweaked right than have to open up the system and add more fluid imo. Open systems have build safety. Closed systems operate on an entirely different principle.
In an open system you can't force more fluid in than the system has volume for, since it will simply go to the reservoir. The reservoir takes or adds fluid from the system as needed. When you fill the reservoir completely, and then force the cover on, you've changed it into a closed system. The procedure your described would work on a closed system, not an open one.

Nope, I can't give you an example of someone who's managed to lock their brakes with an open system. You know why? Because 99.999% of people run them like they're supposed to.
 
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