volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 28, 2017 4:00:46 GMT -5
I got a scooter last month and i have noticed the front disc brake lever is very difficult to press in. I tried bleeding the brakes, greasing the pins, changing brake line and brake fluid and i've also torn down the master cylinder and the caliper itself. After all that work i can't find anything that could be causing the brake lever to be so stiff. It feels like there is too much pressure in the system (which is not true) and whenever i press the lever the bike doesnt stop as it should. Instead it barely brakes at all no matter how much force i apply to the lever. Does anyone have an idea on how to fix this? Thanks
*it is a single piston caliper and all the internal seals are good(MC and caliper)
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Post by 90GTVert on Dec 28, 2017 8:13:47 GMT -5
Since you've tried to bleed it and tore it down, did it feel stiff without fluid? If so, something is up with the master cylinder or lever. Does it have an ABS valve? Can't say I've ever seen it before, but since you've been through most of the system it could be worth finding out if removing that would change anything. It's basically a pressure limiting valve on these. Nothing like a true ABS system. Working properly, it may stop the front brake from locking up simply because it won't apply enough pressure to it... but I've watched a friend lock up his front wheel with an ABS equipped Chinese scooter before.
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 28, 2017 8:37:00 GMT -5
Hi I've tried without fluid it works like a charm. Since i have disassembled everything i would have found such valve if there was one. I also assume such system would be part of the brake line but ive tried with another one and the problem remained.
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Post by pinkscoot on Dec 28, 2017 11:23:46 GMT -5
If it works fine with no fluid and it bled fine then the last place to look would be the caliper. It may be sticking and causing your problems. I would drain it again and make sure the caliper piston moves fine. If the scoot has any age or was sitting it could just be rusted.
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 28, 2017 11:47:19 GMT -5
Thanks for the advice, the scooter had actually been sitting for some time as i was told. However i have disassembled the caliper about three times now and still ι cant see anything wrong... The rubber seal is good and i have cleaned every bit of rust on the pins. That also applies for the master cylinder.
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Post by pinkscoot on Dec 28, 2017 12:52:32 GMT -5
It may be time to just replace the whole thing.
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 29, 2017 10:26:19 GMT -5
Maybe... But still, since i dont use the scooter alot, i dont really want to pay for a new system plus i would like to find what the problem is because it seems very strange to me.
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Post by pinkscoot on Dec 29, 2017 11:25:41 GMT -5
I would assume when you rebuilt the caliper you cleaned all of the passages. Did you put disk brake lubricant on the moving parts? It does seem strange that you have this problem.
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Post by lilpinny on Dec 29, 2017 11:33:37 GMT -5
That membrane rubber thing under the master cylinder is good?
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Post by scoot39 on Dec 29, 2017 12:00:33 GMT -5
Since you tried it without fluid and your brake lever worked fine I don't believe that my fix will be of use to you. I'll pass this along for one more simple fix. My 50cc Puma was having the same problem that you described. Felt like something major to me so I started running the drill. No obvious problems appeared. The stiff brake lever persisted. Saw a tool for greasing cables, and it dawned upon me that perhaps a silicone spray on the lever cable at the handlebar might work. It did. Brakes work just fine now. My only regret is that I didn't try the simple things first.
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 30, 2017 7:46:00 GMT -5
I would assume when you rebuilt the caliper you cleaned all of the passages. Did you put disk brake lubricant on the moving parts? It does seem strange that you have this problem. You mean on the internal rubber seals etc?... yes i did all the times
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 30, 2017 7:48:47 GMT -5
That membrane rubber thing under the master cylinder is good? If you mean the one that is supossed to hold dust away from the master cylinder, yes it is fine.
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Post by lilpinny on Dec 30, 2017 10:12:13 GMT -5
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volvc
Scoot Junior
Posts: 11
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Post by volvc on Dec 30, 2017 11:55:33 GMT -5
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Post by jackrides on Dec 30, 2017 12:37:07 GMT -5
Have you removed the disc pads and pistons? Corrosion can occur where the piston slides in the caliper body. I had a very old vehicle with a strange brake problem, turns out the hose had collapsed inside.
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