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How to diagnose front brake?

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My 07 WR250F front brake is getting spungy.  I can squeeze it hard and it'll travel over an inch and still could not lock up front wheel.  Could that be the master cylinder or the caliper?  If either could cause the symptom, which part should I start and how to test?

It's not air in the system as I can keep pumping the lever and it won't firm up and the action stays the same as described above.

Thanks in advance for any input.

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Well you might as well trying bleeding and replacing thr fluid anyway. Your piston seals could be causing alot of drag also.

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Do you see any fluid by the caliper piston if not it probably is the master cylinder. I am assuming that there is fluid in the master cylinder. It probably is the master cylinder if you have fluid in the reservoir and see no indication of fluid on the brake line or the caliper.

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Air in the system.  Just because you pump the lever multiple times, it doesn't clear the air out of the line.  It just compresses the air over and over and over...

 

To make it easier to bleed, mount your caliper up higher than the master cylinder.  Air will float on brake fluid, and this will help get it all out.  Air tends to get trapped in the arch of the line.

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