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Discussion Starter #1
Hi everyone, just got a used 2015 UE about a month ago. Had about 2800km on it, I've since put on 1000km.

So when I first got the bike, I immediately noticed that the front brake was spongy - brake lever setting on the 2nd closest would touch the throttle. Obviously an air pocket in the line, right? So I flushed the front brakes, and sure enough, bubbles emerged. All good, brake lever was tight, bite on the front brake was aggressive.

Fast forward a month - 2 weeks ago, the brake lever was spongy again! Checked the master cylinder, apart from its position being slightly rotated along the handlebar (not perpendicular to the ground) - nothing out of the ordinary, fluids were filled, all nice and clean. So I flushed it again - bubbles. Put new fluid in, did the whole zip tie for a night thing, minimal improvement. Brakes currently have about 8 - 9mm of play before any bite from the brake, but I hear a click about 3 - 4mm in. This is already "better". Is this normal??

Has this happened to any one of you? Is my master cylinder faulty? Is it something to do with how the fluid line bends?

Thanks in advance for the help!
 

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The click you hear is the micro switch operating the brake light and is normal.
Check all the banjo bolts for pipework are tight. If they are all tight then quickly loosen and re-tighten, this can help re-seat the copper washers.
It has been known for air to migrate in where fluid finds it difficult to come out.
A by-passing master cylinder gives similar symptoms you describe but won’t necessarily let air in as it’s an internal fault.
Remember to check all the banjo
connections under the seat at the ABS unit. I’ve found weepy connections there on a Diavel before.
I also find the best way to bleed the master cylinder is at the top banjo, loosen slightly and tighten AS you pull the lever slowly(use a rag). Brembo master cylinders on the Cafe Racer will have a nipple already fitted, types of Brembo with alloy built-in reservoirs the bleed nipple is inside the tank.
 

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Discussion Starter #3
Thank you for your input, I will take a look.
Is there any way that I could test whether it is the master cylinder that is by passing? Or do I have to bring it in?
 

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Thank you for your input, I will take a look.
Is there any way that I could test whether it is the master cylinder that is by passing? Or do I have to bring it in?
If it’s by-passing it should show by releasing it’s own pressure.
ie; if you hold the brake on, the lever will slowly sink to the bars meaning either air or by-passing. If it goes all the way in to the bars to start with and then the pressure releases, if there are no leaks then it means the fluid/pressure has by-passed the piston seal back into the reservoir.
My guess is air at the ABS unit. It can be a bitch to bleed tbh. best done at the banjos on the ABS unit. I work along the line doing each banjo in turn.
 

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The click you hear is the micro switch operating the brake light and is normal.
Check all the banjo bolts for pipework are tight. If they are all tight then quickly loosen and re-tighten, this can help re-seat the copper washers.
It has been known for air to migrate in where fluid finds it difficult to come out.
A by-passing master cylinder gives similar symptoms you describe but won’t necessarily let air in as it’s an internal fault.
Remember to check all the banjo
connections under the seat at the ABS unit. I’ve found weepy connections there on a Diavel before.
I also find the best way to bleed the master cylinder is at the top banjo, loosen slightly and tighten AS you pull the lever slowly(use a rag). Brembo master cylinders on the Cafe Racer will have a nipple already fitted, types of Brembo with alloy built-in reservoirs the bleed nipple is inside the tank.
I would say in addition to above, if you’ve got all the fluid out replace the copper washers on the banjos. Make sure if you do to use the correct crush washers. If you can’t get them re anneal the originals before re fitting.
 

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I have a 2018 Desert Sled with over 15k on the clock. Standard front brake went spongy like you said, at about 13K. Had it bled and that got me another month.
From the way the dealer behaved, I got the feeling they had seen this all before.
I couldn't be bothered arguing. Bought a Brembo RCS15 and never looked back. And I am working at replacing all lines with braided for improved response.
Nothing worse than brakes you don't trust.
 

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I have a 2018 Desert Sled with over 15k on the clock. Standard front brake went spongy like you said, at about 13K. Had it bled and that got me another month.
From the way the dealer behaved, I got the feeling they had seen this all before.
I couldn't be bothered arguing. Bought a Brembo RCS15 and never looked back. And I am working at replacing all lines with braided for improved response.
Nothing worse than brakes you don't trust.
Don't waste money on new braided lines, the bike already has braided lines from new.
 

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I had the same this morning. After not riding the bike for two weeks no pressure in the front brake.
 

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Discussion Starter #9
I'm going to replace my master cylinder diaphragm and see what happens. I've been around a lot of ducati stores just squeezing the front brakes of different scramblers and they're all pretty spongy, compared to the bikes I've had before. The tech said it was a characteristic of a single disc, but still doesn't explain the loss of pressure...
 
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