Rear brake siezeing up (dot 3?)

3 replies to this topic
  • radish150

Posted October 27, 2007 - 08:56 PM


99 WR400, a while ago my rear brake started to not want to release properly, resulting in a wheel that turned but not easily. I took it to the local yamy shop here (were talking Peru) and the head mechanic took the caliper apart and cleaned it all up, put it all back together and it's doing the same damn thing as before. I mean supposedly the pistons were (still are?) dirty, and were not moving back when the pressure was off. Is it possible that those pistons are fine and the problem is that I have been using dot 3 fluid and it's expanding as things heat up??? Please explain.... :worthy: I guess I should immediately google something on the order of "expanding brake fluid problem".

Tanx velly much.

  • radish150

Posted October 27, 2007 - 09:06 PM


Well, I just answered my own question regarding the brake fluid "expanding". To the contrary the only thing that can happen is it can boil, causing the pedal to go softer rather than harder which is what's going on with me. Seems strange, the pressure just keeps accumulating till the brake won't release. What gives? Can this be fixed or do I need a new/rebuilt caliper?


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  • kjr247

Posted October 28, 2007 - 05:54 PM


The reason the rear brake fluid heats up is that the exhaust pipe runs too close to the rear brake resevoir. I have the same bike with the same problem. The guy I bought the bike from allowed the resevoir to become deformed and let all kinds of stuff in the rear brake line. I took off the master and cleaned it well and everything looked ok. I ordered a new resevoir and fabricated a simple aluminum heat shield to keep things cool. I rode it hard last weekend and the heat shield did keep the temp down. I also started to use a synthetic blend DOT3/4 that takes hi-temps.

I would repair the cylinder (clean it up) and make that shield. I am going to change the rear break fluid often to keep it in shape.

Hope this helps.


  • dmoney1074

Posted October 29, 2007 - 03:57 PM


It's called vapor lock... you NEED NEED NEED to run at least DOT 4... (Bel ray, silkolene, etc.) Otherwise you risk your life...


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