426 back break locking up

7 replies to this topic
  • prodigymark

Posted September 10, 2014 - 03:48 PM


I the last two times I have gone riding I have noticed that my back brake will start rubbing and before I know it I have to stop because it's locking up and bleed it which instantly releases the pressure. The pads are fine, the disc is straight...I thought it was fine until I rode today and the same thing happened... And then again. My mechanics knowledge doesn't go far past maintaining the basics. Any help would be appreciated

  • highmarker

Posted September 10, 2014 - 04:18 PM


Likely a pedal adjustment if you feel that your not dragging the brake.  The rod that pushes into the master cyl has to return out fully for the fluid from the brake caliper to return when your off the brake. If it doesn't, pressure stays in the system dragging the pads, heating the fluid which expands more making more pressure which will lock the brake.  Pedal height screw which hits the frame needs to be set where you want it, then adjust the rod going into the m cyl. so it's retracted with a little freeplay at the pedal end.

  • prodigymark

Posted September 10, 2014 - 04:35 PM


Thank you, I really appreciate it. Would feel pretty dumb taking it to a shop for brakes lol. I work a lot but I will certainly troubleshoot the problem utilizing your advice asap.

  • grayracer513

Posted September 11, 2014 - 07:18 AM


That kind of thing can be the problem, but only in the case where there is a physical return position stop on the pedal.  This is exactly what happens when you use an early front brake lever on the '08 and later bikes; the at-rest position of the piston is too far down the bore and it closes off the return/fill port, trapping the expanding fluid. 


But, there is nothing about the rear brake pedal on a YZ that restricts the travel of the rear master cylinder in any way, and in fact, the master cylinder push rod entirely controls the rear pedal position.


The more probable cause is that the master is too full, or the fluid has water in it.  Buy a new can of DOT4 and flush the old fluid out with it, being sure to fill only to the center of the sight glass.

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  • prodigymark

Posted September 11, 2014 - 09:43 AM


I'll try that, thank you. I had been using dot 3

  • grayracer513

Posted September 11, 2014 - 11:41 AM


DOT3 could be your trouble all by itself.  It has a lower boiling point.  Why would you use DOT3 when the cap and the manual clearly specify DOT4? 

  • prodigymark

Posted September 11, 2014 - 01:21 PM


I just used what was on hand so I could get back to riding

  • prodigymark

Posted September 20, 2014 - 06:35 AM


ImageUploadedByThumper Talk1411223711.881458.jpg
Imagine that, says dot 3 or 4...

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