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Discussion Starter #1
Ever since my crash my front brake has been acting odd.

What I mean by odd is that it maintains pressure 8 times out of 10, but the other 2, it suddenly loses all pressure and I have to squeeze the lever way more than is normal to get any action.

Things I've done so far:

-flushed the system with new fluid
- bled it
- bled it again, somehow there was still some air in there :confused:

It's better now, but still happens, and it's pretty dangerous to be honest.

Does anyone know what could cause this?
 

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I could guess that perhaps your rotor is warped/bent and that's somehow screwing with the pistons in a way that causes the observed problem. Or perhaps your master cylinder has been damaged in some hard to observe way.

But guessing isn't good enough for brakes; you should get an expert opinion and repair from a mechanic ASAP.

Brakes, Oil, Tires, and Chain. Riding with any of those 4 out of whack is gambling.
 

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I could guess that perhaps your rotor is warped/bent and that's somehow screwing with the pistons in a way that causes the observed problem. Or perhaps your master cylinder has been damaged in some hard to observe way.

But guessing isn't good enough for brakes; you should get an expert opinion and repair from a mechanic ASAP.

Brakes, Oil, Tires, and Chain. Riding with any of those 4 out of whack is gambling.
Second that. Sounds like you have a very small bend in your rotor. Which is why sometimes it works and sometimes it doesn't. Take it to the shop and have them check it over.
 

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I don't think the symptoms you described would be caused by a bent rotor. When I had a bent rotor, the front brake 'shuddered' when I squeezed the lever, it never intermittently lost all pressure.
 

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Stop riding it until you find-out what's going on. :eek:

It sounds a lot like the "brake pump-up" problem caused by tight piston seals that would unpredictably pull the pistons back into the cali/off the rotor with them after the brakes were used, wherein the next time the brakes were applied, the lever would need to be pulled further to get the pads back on the rotors for the braking to start. IIRC, some guys were lubing the seals/pistons with a rubber or silicone lube to help keep the pucks on the rotor. Good luck.
 

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Discussion Starter #7
I don't think the symptoms you described would be caused by a bent rotor. When I had a bent rotor, the front brake 'shuddered' when I squeezed the lever, it never intermittently lost all pressure.
The rotor isn't bent, but the spacers holding the rotor were stuck, and that was even before my crash. Got them semi-unstuck and the brake shudder is way less. Have to clean it out with brake cleaner properly.

@vb796

I'm not losing any fluid, which is kind of odd. Seems like there is still some air trapped in the system.

@ stryder,

that seems pretty plausible. I'd have to check my pistons first to see if they maybe got dirty after the crash( whole right side of the bike was full of sand and grass).
 

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Sounds to me like a bad master cyl. When U crashed, did the brake lever get whacked?
Maybe it got poked hard enough to upset the piston + stuff inside the master.

I read again...right side down. Good chance something nasty happened to the master.
 

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Sounds to me like a bad master cyl. When U crashed, did the brake lever get whacked?
Maybe it got poked hard enough to upset the piston + stuff inside the master.

I read again...right side down. Good chance something nasty happened to the master.
I agree!
 

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Stop riding it until you find-out what's going on. :eek:

It sounds a lot like the "brake pump-up" problem caused by tight piston seals that would unpredictably pull the pistons back into the cali/off the rotor with them after the brakes were used, wherein the next time the brakes were applied, the lever would need to be pulled further to get the pads back on the rotors for the braking to start. IIRC, some guys were lubing the seals/pistons with a rubber or silicone lube to help keep the pucks on the rotor. Good luck.

Yes it does sound like a similar situation when you push the piston way in to change pads. The first application does very little braking until pumped out.
 

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Discussion Starter #11
I forgot to add one thing though.

It doesn't matter if I ride the bike or not. If I leave her for the night and want to ride it the next day, I have to pump it before I set out. Fluid levels don't change. I'm gonna bleed it a couple more times to see if it fixes it, my local mechanic said it should, but we'll see.
 

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Dont forget to crack it open at the mastercylinder to burp out any air there. I bleed my clutch endlessly and very meticulously and didnt have a good lever feel until i finally bleed the mastercylinder...
 

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Discussion Starter #13
Dont forget to crack it open at the mastercylinder to burp out any air there. I bleed my clutch endlessly and very meticulously and didnt have a good lever feel until i finally bleed the mastercylinder...
I always bleed the master:D
 

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Discussion Starter #14
Hahahahaha, I'm such an idiot at times :eek:

Today I suddenly remembered that I only bled one of the 2 calipers. I bled the 2nd caliper and voila, out came all the air.
 
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