volvc
Scoot Junior
Posts: 11 
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Post by volvc on Dec 31, 2017 7:49:52 GMT -5
Yes everything seemed fine
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 31, 2017 8:00:23 GMT -5
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Post by GrumpyUnk on Jan 10, 2018 15:17:48 GMT -5
If you drain the master, and then re-assemble it, or close the drain, the fill the master with brake fluid. With the cap removed, work the brake lever. You should be able to move the lever a LONG way, multiple times, each time having a bubble of air come out the tiny hole. If you can't see the hole, or no bubbles, use a pointed utensil to poke into the hole until you get bubbles when you cycle the brake lever.
I had one with a plugged vent that was a hard lever, but it did nothing. Or it was a soft lever that did nothing. It was also in storage for long periods of time. The vent was plugged, and fluid would not get in, so you may have that, and have fluid locked in.
If you can hold the brake lever and loosen the banjo on the caliper, you should get flow around the caliper copper washers. If not, the hose may be damaged internally. If you do get flow, remove the caliper assembly from the fork, and cycle the lever. You should see the piston advance out of the bore. If not, the fluid is not flowing behind the piston, or the piston is stuck in the bore. If the piston advances, press it back into the bore, and re-assemnble. The brakes should work, unless there's a mechanical problem with the pads, blocking their advance towards the rotor.
tom
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Jan 12, 2018 11:33:16 GMT -5
Hi
Thank you for your suggestions
The first thing i tried was cleaning the small return hole you are talking about but it didnt seem to make any difference so the problem remained.
Since i have tried with another hose, without any luck, i dont thing mine is damaged. I haven't tried loosening the banjo while pressing the lever but since i can bleed the system normally i don't think it could be a problem.
Now about the piston, i am sure it is not stuck or sticking because i tore the caliper down and everything is nice and clean.Also i ve tried pressing it in, removing the caliper from the scooter and placing a thick metal sheet between the pads.Then i started pressing the lever multiple times and each time the piston moved closer to the sheet while the lever was very soft.As it reached the metal it started hardening progressively until it became stif (which is my prolem)...
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Post by GrumpyUnk on Jan 12, 2018 14:42:31 GMT -5
What you describe is normal master/caliper action. As you work the lever, the pistons move out and press the pads against the rotor. The pressure developed on the pads is proportional, with the small diameter of the master 'piston' creating high pressure against the caliper piston. There won't be much movement, but the size of the master piston relative to the size of the caliper piston makes the pressure in the pad, in psi or kpa, high. If the brakes don't work, with the caliper moving as noted, then perhaps the pad material is glazed. If applied too gently, over time, the pads will get a 'polished' looking surface, and not be very effective when pressed against the rotor. If so, you can try new pads, or use a sidewalk concrete or garage floor, or concrete block as 'sandpaper' to roughen the pad surface and maybe get the pad to start working again.
If your master is pumping fluid, and your caliper piston is moving, then the thing is working, and it must be the friction material that is dysfunctional. I have read on the web where breaking in new caliper and pads actually requires about 10 'hard stops', where the brakes are applied at ~50-60 mph, hard, and the vehicle brought to a hard stop, then accelerated back to cruise 40-50 for a short while, to cool the rotor, and then repeat the hard stop. The pads and rotors do a 'chemical/mechanical' bond, where the pad material gets embedded into the rotor. The study I read indicated that pedal pulsation could be caused by the pad coming into contact with rotor surface that was 'bonded' with the pad, and then coming into contact with rotor surface further around the rotor, that was NOT 'bonded' as the 10 hard stop surface causes.
My suggestion is to get the thing up to the highest speed you can, safely, and do the hardest stop you can w/o flying over the handlebars, and repeat that about 10 times.
tom
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Post by lilpinny on Jan 12, 2018 20:43:48 GMT -5
Or... buy another.
Sometimes the shit is just broke.
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Jan 13, 2018 10:09:44 GMT -5
What you describe is normal master/caliper action. As you work the lever, the pistons move out and press the pads against the rotor. The pressure developed on the pads is proportional, with the small diameter of the master 'piston' creating high pressure against the caliper piston. There won't be much movement, but the size of the master piston relative to the size of the caliper piston makes the pressure in the pad, in psi or kpa, high. If the brakes don't work, with the caliper moving as noted, then perhaps the pad material is glazed. If applied too gently, over time, the pads will get a 'polished' looking surface, and not be very effective when pressed against the rotor. If so, you can try new pads, or use a sidewalk concrete or garage floor, or concrete block as 'sandpaper' to roughen the pad surface and maybe get the pad to start working again. If your master is pumping fluid, and your caliper piston is moving, then the thing is working, and it must be the friction material that is dysfunctional. I have read on the web where breaking in new caliper and pads actually requires about 10 'hard stops', where the brakes are applied at ~50-60 mph, hard, and the vehicle brought to a hard stop, then accelerated back to cruise 40-50 for a short while, to cool the rotor, and then repeat the hard stop. The pads and rotors do a 'chemical/mechanical' bond, where the pad material gets embedded into the rotor. The study I read indicated that pedal pulsation could be caused by the pad coming into contact with rotor surface that was 'bonded' with the pad, and then coming into contact with rotor surface further around the rotor, that was NOT 'bonded' as the 10 hard stop surface causes. My suggestion is to get the thing up to the highest speed you can, safely, and do the hardest stop you can w/o flying over the handlebars, and repeat that about 10 times. tom Thank you, I'll propably try with another set of pads as i've already tried the "sanding" and the hard stops you are talking about but nothing changed If that doesn't work either i don't know what will... |
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Post by fortyeight on Jan 17, 2018 17:23:39 GMT -5
try a little high tempriture grease on the piston to make it slide easy
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