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Rear master won't pump properly? {Solved!}

Started by Watcher, July 17, 2018, 05:13:59 PM

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Watcher

So I got some new brake pads and brake fluid for my Ducati, in the process of doing a pad change and fluid flush.

I'm having an issue with the rear brake which is driving me a bit nuts, hopefully someone here can help.

Opened the reservoir, removed some fluid, compressed the caliper piston, changed the pads, topped off the reservoir, and now I started the fluid change process.  Tube on the bleeder, pedal down, open bleeder, close bleeder, pedal up, top fluid, rinse and repeat.  A couple of pumps in the pedal stops giving me resistance, and now no matter how many times I pump that damn pedal it never builds up pressure.

I think maybe I fudged it from the bleeder and it back flowed air somehow.  So I go and buy a vacuum bleeder kit.  Get that all squared away, and even though I can suck fluid through the system from the nipple it doesn't solve the problem.


I figure on taking a break from that system, so I move to the front brake.  Vacuum system on, vacuum pumped up, open bleeder, it draws fluid, close bleeder, top off, rinse and repeat until I see clean fluid coming out.  Button it all up, test the system, perfect!
On to the clutch.  Same process as the front brake, test the system, perfect!
Old fluid I got out of the clutch looked like Snapple Peach-Tea, gross!
I actually go test ride around the parking lot at this point.  Clutch feels about the same as it did before, but the front brake feels AMAZING!


Back to the rear.  I can get a teensy little bit of pressure at the very end of the pedal's travel.  The pedal will depress to about a half inch from the exhaust, when I open the bleeder it will depress all the way to the exhaust, then I close the bleeder and try and get more pressure in it and it gives me the exact same thing every time.  It never improves.
At this point I used over a half a bottle of brake fluid in that system, it keeps coming out and going in but it won't get the air out.

I have not touched any of the banjos or the feed line from the reservoir.  None of those fittings were leaking, nor are they now, and neither is the caliper itself.  I doubt the master has gone bad, it was working beautifully for the life of the bike and only started having issues now that I've tried to flush the system.
I think my next step (and it's gonna be a messy one) is to crack the banjos and see if I can get those to bleed.  I'm wondering if an air bubble has traveled up from the bleeder all the way to the banjo at the master and has become trapped there somehow.
"The point of a journey is not to arrive..."

-Neil Peart

Watcher

Bled at the master banjo, no bubbles.

Then I went and dismounted the caliper, recompressed the piston, gave the pedal a push and watched to make sure it was sliding properly.

Then I had a thought.  On the bike the caliper is mounted under the swingarm with the bleeder pointing down.
I set it on the rotor with the bleeder pointing up and tried to bleed it.  SUCCESS!

I'm not even going to question it, pedal feels very firm now.  Haven't test ridden it yet gonna get cleaned up first, might update with a report on the performance.

I got EBC HH pads all around, sintered rear pads and some high-performance sintered street/track front pads.  Also used RedLine RL-600 DOT4 fluid in everything.  Had a higher boiling point than even BelRay 5.1, so hell yeah!
Front brake feels like I can now do with 2 fingers what I could do with 4, and I always though the Duck had good brakes.  Now to see what the rear can do!
"The point of a journey is not to arrive..."

-Neil Peart

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