XR 250R RIDER

Member
Apr 5, 2001
58
0
I have an 02 RM 85 and now once during a race and another time the front brake has locked up. I can feel it slowly getting excessive drag and then it totally locks up. We cleaned out the caliper bore then put in new piston seal and dust seals and bled the brakes, it appears the piston and caliper bore are fine with no nicks or marks on them. I made sure I don't have too much brake fluid, my pads are fine. I seems that they work fine when cold but act up once the brakes start warming up.

Anybody have any ideas on what to do?
Anybody had similiar problems?
 

ACS

Member
Apr 17, 2001
242
0
Double check that you have a tiny bit of freeplay at the lever. If you dont the heat can expand the fluid and it locks up esp if the lever is in far enough to block the "bypass bleed" in the mastercylinder.
 

kdx633

Member
Aug 12, 2003
127
0
problem is definately heat related,was replacement fluid "new from sealed container".brake fluid absorbs water from the atmosphere which expands greatly when subjected to heat generated by braking.also was the new flui the same "dot" #.
 

Jasle

Sponsoring Member
Nov 27, 2001
1,358
0
I'd be interested in if the fluid was the correct type but if you used say dot 3 instead of dot 4 the main difference is the wet and dry boiling temp. Dot 3 boils at a lower temp. This usually leads to a mushy lever. This is due to the fluid boiling off water that has been absorbed and then the boiled water causes a vapor which is compressable.
Try riding some practice and wait until the problem surfaces. Then pull off while the disc is grabbing and open the bleeder. If fluids squirts out instead of dribbles then you could have a brake line "check valving" you might need to replace the hose. Also I have seen this exact problem when someone put some oil in the brake fluid resivoir. The petroleum based oil attacks the rubber lines and causes them to expand.

Lever freeplay is crucial as mentioned before.
 

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