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Discussion Starter · #1 ·
I've got Avid Juicy Ultimate 7 (the brakes of a Specialized Stumpjumper Fsr Expert).
Last week I've had problems with my braking power if I drive down over rocky terrain, so with a lot of small bumps. If I try to brake after this or on it, I will have lost most of my brake power. At a certain moment I was even able to pull the levers to the handlebar completely on both sides with near to no braking power. If I pump the levers a couple of times, the power comes back. After this the brakes feel solid, so not as if there is air in them.
The brakes have been bled a couple of months ago, the rear even only a couple of weeks ago. What could cause this problem? Is there maybe not enough brake fluid in the system?
I presume that I have to bleed the brakes yet again.
 

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Yup, bleed em....

there's air in there some where. There are lots of places for air bubbles to hide in a hydro disc system. When you hit the chatter bumps your breaking them loose and they are affecting the system. Follow Avid's bleed procedure to the letter, and as you bleed tap the caliper, lines, and the master cilynder firmly with your finger or a plastic tool, I've found that a rubber coated cone wrench handle works well. You don't have to beat anything just a couple of firm taps now and then as you are working through the bleed process. It helps to break loose those clingy little bubbles that like to stick to the inner surfaces of the caliper and lines.

Good Dirt
 

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Yup, exactly what Squash said. If you're using the actual Juicy Bleed Kit with the syringes, you should be able to pull almost all of the air out of the system if you follow the directions. That kit works really well.
 

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The symptoms you describe sound similar to something that can happen on motorbikes after having a tank slapper. A tank slapper is when a motorbike shakes the front wheel violantly from side to side when accelerating hard. This is so violant that the pistons are pushed back inside the caliper, so when you pull on the lever it comes back to the bars and it takes several pumps to get the pistons back in to position.

I have never heard of this being caused by bumps before though as it normally requires a side to side movement, but I though I would mention it as it sounds so similar.
 

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similar probem - Juicy 5s

I just bought an enduro SL comp with J-5s and finding that when I am aggressively riding downhill, I loose brake pressure (read - this is bad). Levers go down to the handelbars. I had my LBS rebleed them, to no avail. I will look into making sure they are doing it correctly and report back any success.
 

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endo-boy said:
I just bought an enduro SL comp with J-5s and finding that when I am aggressively riding downhill, I loose brake pressure (read - this is bad). Levers go down to the handelbars. I had my LBS rebleed them, to no avail. I will look into making sure they are doing it correctly and report back any success.
if you are really agressive and are a bigger rider - you might be boiling the fluid and that's why you're losing your brakes on DH... despite repeated bleeding...

what pads are you running? sintered metallic? (they will have copper backing plates usually)... switch to those if not using them already... or something like EBC reds or other pads recommended for DHing...

what fluid are you using? if DOT 4, switch to DOT 5.1... or maybe check with Avid if you can run SUPER DOT 4 (higher boiling point)... (DOT 4 has dry boiling point of 230C, DOT 5.1 270C, and SUPER DOT 4 280C.... wet boiling points are 155C/191C/186C respectively)

or maybe also try bigger rotors (203's) to dissipate the heat.... (assuming you're not already - ie. if you have 185/160's)

cheaper to try the above than to swap brakes to another brand... but if all else fails...

cheers

(P.S. I wonder if this brake fluid is safe for use with Juicy's.... http://www.pegasusautoracing.com/productselection.asp?Product=3343... Castrol SRF... only $80 per liter!!! :D )
 

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An update to my situation. I got the run-around from the LBS after bringing back the bike once again, but insisted they where full of crap.

No, hanging your bike upside down does not force hydralic fluid behind the cylinders and cause fading.

No, pumping them once or twice does not fix the problem.

And no, you did not get all the air out.....

They got another mechanic to look it over and to my satisfaction was told "Hey, I got the air bubbles out". Now they work like a dream (or at least much better).
 

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I bought a 2008 fuel EX with Juicy 5 set.

I have had the exact same problem when riding fast on bumpy downhill terrain. My levers became "soft" and I was able to pull them back all the way to the handlebar. Although I first thought this may have been due to heating, I can say that I´ve tried braking on even faster, steeper descents and the brakes work perfectly. I´ll try the bleeding and get back with news. Thanks for the advice.
 

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Discussion Starter · #10 ·
After bleeding mine yet again at that time, it did solve the problem.
The strange thing was that I only got air bubbles coming out of the lever, and completely nothing at the side of the caliper.
 
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