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Discussion Starter #1
Decided to bleed the rear brake, fluid was dark and bored, done this several times before and not problems till now. Rear brake was working fine before I bleed, did traditional way by depressing pedal and opening valve and filling up reservoir. All the old fluid was out and brake won't hold pressure, maybe air was still in the line, so did a reverse bleed and looked while reservoir was being fill for air coming up and none. So now it still won't hold any pressure, caliper pistons are pushing pads to rotor but not enough to stop the bike. Should I just get a master cylinder rebuild for the rear or could it be something else?

Thanks.


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Sounds like you still have some trapped air somewhere in the system. Sometimes I will press down on the pedal, crack open the banjo bolt(s) and then quickly tighten it up before releasing the pedal again. My KTM dirtbikes seem to get air trapped right where the brake line attaches to the master cylinder, even when back-filling the system with a syringe. Final bleeding by cracking open that connection takes care of it.
 

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Air is not trapped in the line, but in the caliper.
Check your caliper, the bleeder is pointing down, the air is trapped in the upper part of the caliper.

To bleed, you have to flip the caliper upside down.
 

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Air is not trapped in the line, but in the caliper.
Check your caliper, the bleeder is pointing down, the air is trapped in the upper part of the caliper.

To bleed, you have to flip the caliper upside down.
+1

Also, I've had a rear caliper on my track bike lose pressure due to fluid caking up from not being used. I had to dissamble the caliper and banjo bolts, blow/clean it out and it worked fine after that.
 

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And it is such a small system it only takes a very small amount of air to make the rear brake virtually useless.
 

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Discussion Starter #6
Air is not trapped in the line, but in the caliper.
Check your caliper, the bleeder is pointing down, the air is trapped in the upper part of the caliper.

To bleed, you have to flip the caliper upside down.
Thanks for the tip, I'll try that tonight once I get off work.


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Discussion Starter #7
Thanks a million!!! That worked perfectly, saw a couple of bubble pass through the bleeder hose and top off the fluid now pedal is hard as a rock. Great tip will definitely keep in mind next time I or someone else has the same problem.


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To bleed, you have to flip the caliper upside down.
Yep that is exactly it. I just in fact bled my system a couple of weeks ago and I had to take the caliper off and point the bleed nipple up. What idiot "engineer" decided to put the bleed nipple at the bottom anyway? :mad:

BTW, Chouch or anyone for that matter, were you ever able to get the rear brake lever of the Hyper rock hard? It seems no matter what I do, it never seems to be as hard and air-free as my other bikes. In fact, it was a little soft when I got it brand new. :think:
 

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BTW, Chouch or anyone for that matter, were you ever able to get the rear brake lever of the Hyper rock hard? It seems no matter what I do, it never seems to be as hard and air-free as my other bikes. In fact, it was a little soft when I got it brand new. :think:
Sadly no, or at least not as hard as I would like it be.
After bleeding it's decent, but quickly fade after a few hundreds miles.

If you want a very cool and rare mod/upgrade/bling, this is what you need.
DUCATI HYPERMOTARD PINZA POSTERIORE RADIALE IN ERGAL | eBay
 

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Air is not trapped in the line, but in the caliper.
Check your caliper, the bleeder is pointing down, the air is trapped in the upper part of the caliper.

To bleed, you have to flip the caliper upside down.
Ok, so trying this, and as I said in my intro, totally new. I was trying to loosen the rear caliper and the bolt appears to require an unusual sized hex...5.5 mm seems too loose, with the hex rotating in the head and appearing close to stripping it out. The 6 mm is too large.

Am I missing something?

(2011 796)
 
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