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Old 02-22-09, 08:05 PM   #1
Lebowski
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questioning the hydraulic brakes

i got a set of avid j5's the rear brake always seemed to have disproportionally less braking power than the fronts. i am fully aware the front brakes have most of the braking power vs the rears.

i have to pull the lever very far (near the handlebars) to get a response from the brakes, and the response is good. i'd rather they be real sensitive so i can pump them rapidly with one finger.

i had the brakes bled professionally at the bike shop recently. (the bike isn't that old to begin with) it didn't solve the problem. is there a way to adjust them? how about that little hex nut inside the lever? would that fix the reach issue?

:edit:
could this be an issue with the rear hose being more than twice the length of the front hose? do i have to physically pull the lever farther to push the fluid farther distances?
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Old 02-23-09, 03:38 AM   #2
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Originally Posted by Lebowski View Post
could this be an issue with the rear hose being more than twice the length of the front hose?
Yes, in two ways:
1) longer hose is harder to bleed "perfectly". You may have small bubbles all along its length, making the braking mushier.
2) IF the brake hose expands a little by the pressure, then a longer hose means that you're losing more volume to to hose expansion in the rear.

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do i have to physically pull the lever farther to push the fluid farther distances?
No. Fluids are considered incompressible, so any change at one end should immediately be translated ito the corresponding change at the other end.
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Old 02-23-09, 06:41 AM   #3
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so is it a matter of adjusting the reach on the lever?
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Old 02-23-09, 09:35 AM   #4
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Lever reach is only going to change the starting point of the lever, it's used to accommodate hand size.
J5s should work better than that, suspect your shop didn't do such a hot job of bleeding or didn't solve another issue that may exist (and they should have investigated if they couldn't solve the problem with the bleed)...
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Old 02-23-09, 09:42 AM   #5
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Could it be a misadjustment of pads or calipers? Perhaps if the pistons simply have to move too far, that could be it.

Does it feel like braking power gradually increases as you pull the lever farther, or is it like you have nothing and then all of a sudden *wham*?
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Old 02-23-09, 09:44 AM   #6
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So, I can bleed brakes quite well on a car, and I *think* I know how to bleed brakes on a bike (squeeze a couple times, hold the squeeze, slightly loosen the bleed valve and let fluid come out, close the bleed valve, build pressure back up, wash, rinse, repeat, all the while making sure the fluid level in the reservoir doesn't get low), but am I missing something, because I have the same problem with my rear brakes on my MTB (Shimano America LX hydraulic discs) The rear brake won't lock up the rear tire when I am going downhill, and it will squeak horrendously after I brake with it for about 5-10 seconds

So, am I missing something?

Sorry to threadjack, BTW, but I have the same exact problem, just different brand of brakes.
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Old 02-23-09, 09:51 AM   #7
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So, I can bleed brakes quite well on a car, and I *think* I know how to bleed brakes on a bike (squeeze a couple times, hold the squeeze, slightly loosen the bleed valve and let fluid come out, close the bleed valve, build pressure back up, wash, rinse, repeat, all the while making sure the fluid level in the reservoir doesn't get low), but am I missing something, because I have the same problem with my rear brakes on my MTB (Shimano America LX hydraulic discs) The rear brake won't lock up the rear tire when I am going downhill, and it will squeak horrendously after I brake with it for about 5-10 seconds

So, am I missing something?

Sorry to threadjack, BTW, but I have the same exact problem, just different brand of brakes.
Not same problem, OP just wants to engage sooner, says they work fine once they engage. In your case not enough info, could be a variety of issues but I'd look at pad/rotor contamination.
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Old 02-23-09, 03:05 PM   #8
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Originally Posted by Mr. Underbridge View Post
Could it be a misadjustment of pads or calipers? Perhaps if the pistons simply have to move too far, that could be it.

Does it feel like braking power gradually increases as you pull the lever farther, or is it like you have nothing and then all of a sudden *wham*?
nothing then "wham"

i am beginning to wonder if they actually bled the brakes
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Old 02-23-09, 04:02 PM   #9
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Not same problem, OP just wants to engage sooner, says they work fine once they engage. In your case not enough info, could be a variety of issues but I'd look at pad/rotor contamination.
Huh, ok, I will check that
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