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Rear brake lockup YZ125 05

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Hi guys

 

My rear brake keeps on locking up after about 10 minutes of riding on a hard track. It gets super hot and the brake pedal becomes stone hard. I have tried all the possible things i can think of:

 

Bleeding the brake

Cleaned everything, put new seals in the caliper, and given the master cylinder a new repair kit

Adjustet the height of the rear brake pedal so that it is zero with footpegs

 

Things to mention:

I ride with Dot4 fluid

One of the union bolts are from another machine (don't know if that has anything to say?) 

The rear brake pedal is worn where it connects to the master cylinder (again don't know if that has anything to say?) 

 

 

I really hope you guys have a clue on what to do because it is driving me insane!

 

 

- Mathias 

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you have to make sure the rear master cylinder is not being compressed at all when the brake pedal is not compressed. simple as that, if the brake is too mushy after being properly adjusted you need to bleed the system.

 

basically you are expanding the fluid and it has nowhere to go which pressurizes the system causing more braking and heat making the problem worse and worse.

Edited by Wild Alaskan
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So basically what you are saying is that there is still air in my system? - I forgot to mention that when it locks up i just bleed it quick and it will work again for some time.. 

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You could also possibly have too much brake fluid in the reservoir. Once it heats up it will expand, if it has no where to go it will pressurize the caliper.

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Im thinking a warped disc, or maybe your caliper is seized on the little sliders in such a way out holds on side on the disc with pressure. That would cause it to heat up the fluid to a point it looked the brakes

Edit, auto-correct

Edited by zotis777

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It moves freely on the sliders, i have just had it cleaned and lubed up with rubber grease. The disc seems fine, don't think it is warped..

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