Extremely firm front disc brake - Motorcycle Forum
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post #1 of 19 (permalink) Old 04-20-2017, 03:33 PM Thread Starter
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Extremely firm front disc brake

I bought a scooter last week and i have noticed the front disc brake is very difficult to press in.
I checked the fluid and greased the pins but it did nothing. The bike only stops instantly because the lever doesn't move at all unless i press really hard and even then it travels only half a cm or so, in other words i can't push the lever progressively to stop the bike normally.
Haven't bled the system yet but i have heard that bleeding does the job for a spongy lever and i have the exact opposite feel.
Any ideas on how to fix this?
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post #2 of 19 (permalink) Old 04-20-2017, 04:09 PM
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I would be interested to know what happens if you crack the bleeder screw for a couple seconds and then tighten it again. Does it change he feel of the lever?
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post #3 of 19 (permalink) Old 04-20-2017, 04:23 PM
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change out your fluid, crack the bleeder valves let some air in, change the fluid, then bleed the system. this should reset your system completely and eliminate this feeling. otherwise, it sounds like perhaps the caliper is not opening completely.
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post #4 of 19 (permalink) Old 04-20-2017, 08:53 PM
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^^^That would be my guess too: That the caliper isn't opening properly, and that could be caused by a few things. If your brake disk gets abnormally hot from riding without braking that would also tend to confirm the caliper isn't opening all the way.
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post #5 of 19 (permalink) Old 04-21-2017, 01:17 AM Thread Starter
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Quote:
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change out your fluid, crack the bleeder valves let some air in, change the fluid, then bleed the system. this should reset your system completely and eliminate this feeling. otherwise, it sounds like perhaps the caliper is not opening completely.
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^^^That would be my guess too: That the caliper isn't opening properly, and that could be caused by a few things. If your brake disk gets abnormally hot from riding without braking that would also tend to confirm the caliper isn't opening all the way.
I dont think the caliper is the problem because i lifted the bike and the front wheel spinned freely (i mean as it should) and i haven't noticed it heating up either..
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post #6 of 19 (permalink) Old 04-21-2017, 02:26 AM
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Did you check if the pistons are going through their full range of motion?
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post #7 of 19 (permalink) Old 04-21-2017, 07:15 AM Thread Starter
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Did you check if the pistons are going through their full range of motion?
yes, i pressed them in and as i pushed the lever they came out until they became stiff and really hard to press again
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post #8 of 19 (permalink) Old 04-21-2017, 07:24 AM
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Then my next guess would be you have a damaged caliper piston or bore.

Might also be a clogged pressure relief hole in the master cylinder, or a damaged plunger / bore in the master cylinder.
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post #9 of 19 (permalink) Old 04-21-2017, 08:50 AM
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What EYE said

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post #10 of 19 (permalink) Old 04-21-2017, 11:27 AM
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caliper rebuild time, while youre at it you said the wheel spins freely, but check disc for warpage/runout anyway. For your troubles you get fresh clean fluid
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post #11 of 19 (permalink) Old 04-21-2017, 11:46 AM
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Quote:
Originally Posted by Eye_m_no_angel View Post
Then my next guess would be you have a damaged caliper piston or bore.

Might also be a clogged pressure relief hole in the master cylinder, or a damaged plunger / bore in the master cylinder.
Agreed. That's where I was going when I suggested cracking he bleeder. It sounds like excessive pressure due to either a bad relief or damaged MC.
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post #12 of 19 (permalink) Old 04-24-2017, 01:23 PM Thread Starter
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Update: I bled the system (new fluid etc) and everything seemed fine, the lever felt great as it should. However after some stops it started hardening again. Now it has become really firm again and i am right back to where i started from...
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post #13 of 19 (permalink) Old 04-24-2017, 01:36 PM
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Update: I bled the system (new fluid etc) and everything seemed fine, the lever felt great as it should. However after some stops it started hardening again. Now it has become really firm again and i am right back to where i started from...
that is sounding like your caliper isn't opening all the way perhaps taking it off and resetting it? only other thing I can figure would be that the master cylinder has a bad seal or a clog. or perhaps the plungr behind the piston needs repair. something in the system is not relieving enough pressure so it is staying in the system. it could even be just as simple as a kink in the line somewhere. in all honesty what I would do because I just like tinkering with things, I would take the caliper apart to investigate what is wrong could be something simple inside the caliper but if all else fails, get a new caliper odds are it wouldn't cost too much for it.


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Last edited by DavidSkinner; 04-24-2017 at 01:43 PM.
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post #14 of 19 (permalink) Old 04-24-2017, 01:44 PM Thread Starter
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Quote:
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that is sounding like your caliper isn't opening all the way perhaps taking it off and resetting it? only other thing I can figure would be that the master cylinder has a bad seal. something in the system is not relieving enough pressure so it is staying in the system.
If by resetting you mean pushing it back in i have done that multiple times and after some pushes of the lever it becomes firm again. I haven't checked the seal yet but someone suggested that i had a clogged pressure relief hole. Unfortunately i don't know exactly how to diagnose such thing or fix it...could someone please help me out with this?
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post #15 of 19 (permalink) Old 04-24-2017, 02:03 PM
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If by resetting you mean pushing it back in i have done that multiple times and after some pushes of the lever it becomes firm again. I haven't checked the seal yet but someone suggested that i had a clogged pressure relief hole. Unfortunately i don't know exactly how to diagnose such thing or fix it...could someone please help me out with this?
the pressure relief is at the bottom of the cylinder. and by resetting I mean completely disconnecting the caliper( take it off along with the brake pad) and pushing the cylinder back then put the brake pad on. it's almost like an extensive brake pad change. in order to unclog the relief hole, take the holes from underneath after draining the sytem, and blow it out and clean it which can be done with just about any type of automotive cleaner.


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post #16 of 19 (permalink) Old 04-24-2017, 04:05 PM
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If you can open up your master cylinder and not spill the fluid, try looking around the bottom for a really tiny hole (or a clogged one). They're small, but if you can push a pin through it that will open it up and relieve the pressure.

Probably better to take it apart like David said, but the quick and dirty way will get you back on the road.
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post #17 of 19 (permalink) Old 04-25-2017, 08:42 AM Thread Starter
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Quote:
Originally Posted by cmonSTART View Post
If you can open up your master cylinder and not spill the fluid, try looking around the bottom for a really tiny hole (or a clogged one). They're small, but if you can push a pin through it that will open it up and relieve the pressure.

Probably better to take it apart like David said, but the quick and dirty way will get you back on the road.
I can see the big and the small hole but the small one isn't that small looking it from the top. It looks like its clogged and i assume there is a smaller hole, the actual hole, in the center of this small hole. Anyways i will try with a pin and hopefully that fixes it. Thanks!
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post #18 of 19 (permalink) Old 04-25-2017, 11:58 AM
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I can see the big and the small hole but the small one isn't that small looking it from the top. It looks like its clogged and i assume there is a smaller hole, the actual hole, in the center of this small hole. Anyways i will try with a pin and hopefully that fixes it. Thanks!
yes, that's what you're looking for. just put it in there and kinda circle it around the sides of the hole. if a little fluid comes out don't be surprised because it is a relief hole that is not relieving.


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post #19 of 19 (permalink) Old 04-25-2017, 11:59 AM
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and not sure if you know it or not already, but never pull the brake if there is no fluid. just a fyi for later possible experiences.
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