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Discussion Starter #1
I have a Desert Sled, now 3 months old and 3000 km. Three weeks ago the rear brake failed, no warning, pedal just went to the metal. Ducati now tells me it wasn't air but instead I had contaminated the fluid by riding the bike off road. They are just shitting me right? What do you guys think?
 

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They’re shitting you.

It’s a closed system. Dirt can’t get in. A brake doesn’t know the difference between road grime, dust or offroad dirt.
This happened before on quite a few Scramblers. It’s the rear master cylinder seals...
 

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Discussion Starter #3
Thanks for that Max. If the seals are dissolving slowly then I guess I will keep on getting air in the system. Is it the material the seals are made of or the fluid compatability do you think?
 

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I think it could be the mc's piston seal, which means it doesn't necessarily trap air.

I know Henry crew had a similar issue.
 

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Yes, I understand, if the seal is bad then the cylinder operation can just recirculate fluid rather than operate the slave. Henry's brake issue was after quite a few kms I believe. I would change the cylinder, the dreadful cheap reservoir and install a heat shield and ceramic washers if I could find an aftermarket kit
 

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Replace the bellows seal. A very common issue on enduro bikes w/Brembo's. When the oil gets hot, a worn bellows seal can soften or change shape and allow the oil to pass by - pedal goes to the floor and no pressure to actuate the cylinders - system cools and brakes work fine. If the pedal goes to the floor while the circuit is cool then the seal has failed. Brembo sells them 5 to a box for about $10.00.
 

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Discussion Starter #7
Well that sounds like it! I guess you do not mean the bellows I can see at the bottom of the cylinder outside the cylinder which must just be a dust seal. So is the seal inside the cylinder a bellows too rather than just an 'O' ring? And a daft question: Do Brembo make the master cylinder on these bikes 'cos I see no name on it? Whilst we are at it, any idea where I can source a reasonabke reservoir and a proper tube rather than the cheap crap that Ducati has fitted. Also anybody come up with a heat shield to stop the exhaust cooking the fluid? Thanks for your help mate.
Replace the bellows seal. A very common issue on enduro bikes w/Brembo's. When the oil gets hot, a worn bellows seal can soften or change shape and allow the oil to pass by - pedal goes to the floor and no pressure to actuate the cylinders - system cools and brakes work fine. If the pedal goes to the floor while the circuit is cool then the seal has failed. Brembo sells them 5 to a box for about $10.00.
 

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From the manual:

REAR
With fixed drilled steel disk.
Disk diameter: 9.6 in (245 mm).
Hydraulically operated by a pedal on RH side.
Make: BREMBO
Type: PF32 b (black).
Friction material: FERIT I/D 450 FF.
Cylinder type: PS 11

A complete rebuild kit for the rear should run about $25.00 US (at least that's what I pay for my KTM's).
What you see from the outside is a dust seal. I have a '17 Desert Sled and just checked- and dang that exhaust is pretty close to the master cylinder - I'll be afraid to slow down!
 
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