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 locked rear brake

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bigg

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PostSubject: locked rear brake   Mon Jun 11, 2012 10:33 am

Just noticed today my rear brake pretty much is not working at ALL. I have to stomp it down with all my force to get some sort of action, but it takes like 20 meters to slow down from 10 kmh. impossible to lock the brake.

Had a look and it appears that the right pad is not moving as it should. It pretty much stays where it is, pretty close to the rotor but not touching. I tried some wd-40 on the metal rod holding the pads where they slide (looked pretty encrusted), but pad probably only moves 1/10 of a mm or so.

what could be causing this?

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Arkmage




PostSubject: Re: locked rear brake   Mon Jun 11, 2012 11:35 am

When was the last time you bled the rear brake? I did mine at 11K miles and it was pretty gnarly crap that came out. The feel at the pedal after ward was substantially improved.
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bigg

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PostSubject: Re: locked rear brake   Mon Jun 11, 2012 11:45 am

I'm now at 11,000 km (6800 miles), never bled the brakes...

Next week I have to go to the yammi dealer for the the 10,000 km check up (bike still under warranty), but would like them to do as little as possible. (paid 60 Euro for a f**king oil change at 5000 km, damn warranty is killing me!!)

would bleeding the brakes solve such an issue though? I'm puzzled because the pad pretty much can't be pushed in... no matter how hard I stomp on the brake, it moves just fractions of a mm... (enough to make contact with the disc but not with enough force for any reasonable braking performance)
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motokid
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PostSubject: Re: locked rear brake   Mon Jun 11, 2012 12:06 pm

Unbolt caliper from bike.
Remove pads.
Use a c-clamp to slowly compress piston in caliper.

Check seals, and while in there clean and grease things.

The caliper piston should be able to be compressed with a c-clamp.

Not sure if the rear brake on our bikes has one pad that's stationary and one that moves, or if both compress the disc.

At any rate, I'd remove the caliper and inspect, clean, lube/grease, and see if that piston inside caliper moves or is stuck.




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2008 WR250X
Gearing: 13t - 48t
Power Commander 5 / PC-V
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FmF Q4
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pbnut

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PostSubject: Re: locked rear brake   Tue Jun 12, 2012 9:55 am

Sounds like pad pins to me. You said yourself that they look "pretty encrusted". I believe it's an allen head grub screw that you remove and then the pad pin is behind that. Pull the pin and clean it up. The pads need to be able to slide on that pin in order to pwrk correctly. I'd be willing to bet it's in the regular maintenance section of the manual.
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bigg

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PostSubject: Re: locked rear brake   Tue Jun 12, 2012 1:15 pm

After my post I went down to remove the pin and gave it a thorough clean with wd-40. Looks almost new now but I can't really tell much difference. Maybe a small improvement. still not anywhere near where it should be.

How would I know that the brake needs bleeding? Is this a common side effect? To pretty much loose 80% braking performance? Shog excuse my possibly silly questions but I never bled brakes before, wrr first bike other than my old scooter.

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Arkmage




PostSubject: Re: locked rear brake   Tue Jun 12, 2012 5:37 pm

bigg wrote:
After my post I went down to remove the pin and gave it a thorough clean with wd-40. Looks almost new now but I can't really tell much difference. Maybe a small improvement. still not anywhere near where it should be.

How would I know that the brake needs bleeding? Is this a common side effect? To pretty much loose 80% braking performance? Shog excuse my possibly silly questions but I never bled brakes before, wrr first bike other than my old scooter.


You're at the mileage now that you should bleed the brakes as standard maintenance anyways. If you get air in the lines then you'll be unable to generate good pressure as the air compresses rather than the hydraulic fluid relaying your force to the piston. Another reason to bleed the brakes is that brake fluid is hygroscopic, which means it absorbs water... and it can rust your master cylinder and/or caliper pistons.

First step in diagnosing any brake feel problem should be to check you pads... next step is to bleed the brakes. It only takes a few minutes per axle.
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bigg

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PostSubject: Re: locked rear brake   Wed Jun 13, 2012 12:07 pm

After some more "testing" I think the pedal does feel a bit mushy.

Looks like I'm in for some DOT4.

I'll let you know how it goes.
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