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Old 10-09-2017, 01:05 PM   #1
Aphex
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Weird front brake issue.

Alright so the bike is a 2007/2008 Superduke 990 with a Brembo MC and calipers.

I recently installed new Vesrah pads on the front calipers, I cleaned the pistons with a toothbrush and warm soapy water then replaced the old fluid by sucking 90% of the old fluid out of the res with a large gauge syringe, replacing the fluid then bleeding at the calipers until the fluid ran clear. Then I bled at the lever.

So here is the weird issue.

Under heavy braking the lever is rock solid, anytime I engage the brakes to actually stop they are rock solid and the lever never gives or feels spongy.

However if I'm creeping to a stop and I'm just barely applying enough pressure to drag the pads on the rotors then the lever will very slowly travel all the way to the bar, however if at anytime I apply more pressure while the lever is traveling towards the bar the lever will get rock solid again.

Fluid isn't leaking from any of the bleed nipples, fittings or distribution block under the headstock, and the fluid level is not dropping in the res when this happens.

Now this only happens when I'm moving. If I apply the same pressure when at a stop the lever acts as it should. However if I gently push the bike forward the lever will start to creep towards the bar.

Does it sound like it's time for an MC rebuild? It just feels like there is a pinhole leak or something in a diaphragm in the MC. The only other time I've ever felt anything like this was on a car with a bad brake booster.
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Old 10-09-2017, 02:39 PM   #2
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Did you fully decompress the caliper pistons after you cleaned and installed the new pads? That tends to help even out the pressure and bite...
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Old 10-09-2017, 03:45 PM   #3
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Yeah, I pulled the old pads and pumped the lever to expose most of the pistons (while holding down the ones moving faster than others to get them all even) then cleaned them, pushed them back in and made sure they were all moving at about the same speed.

Then pushed them all back in flush with the caliper body before installing the new pads.
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Old 10-09-2017, 05:20 PM   #4
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Sounds like a weird pinhole leak situation to me.

I would begin by changing the internals on the MC.
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Old 10-09-2017, 06:11 PM   #5
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sounds like MC needs a rebuild. Had the same issue with my truck. Replaced the booster and problem was still there. Replaced the mc and it was like new again.

Last edited by FFF; 10-09-2017 at 06:42 PM.
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Old 10-09-2017, 09:46 PM   #6
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Could be an air bubble still somewhere in the line. The way you say it happens only when moving and just moving a little forward. A bubble would behave and move that way when you move. Anyway I would bleed the lines thoroughly again before getting all surgical with it.
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Old 10-21-2017, 07:16 AM   #7
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You may have bled it the opposite way. Bleed at the MC first, then at the calipers.
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Old 10-23-2017, 11:48 AM   #8
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I would recommend you bleed the MC, then left caliper, and right caliper last. I usually tap the area around the brake lines as I'm bleeding to knock any bubbles (don't know if this actually does anything, but seems to work).
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Old 10-23-2017, 12:56 PM   #9
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Have you tried tying the lever back overnight with a tie wrap?
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