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Discussion Starter #1
ok guys, here goes. i installed my 636 master/calipers about 2 months ago. used it for 2 trackdays, no fade at all either time. bled them thuroughly after the 2nd day. have dot5 fluid in them. stock lines, stock pads. they have been AWESOME from day one. then, wednesday going to work, i go to back down the driveway and almost crash, no brakes. lever went to the bar, no resistance at all. i pumped it up, and it was fine. rode to work, and by the time i got to work (about 3 miles) it was normal. then it was fine for two days. this morning, same damn thing, no lever whatsoever. this time, i pumped it up a lot, it didnt get much better. i rode to work (shouldnt have probably) and it never got to the same feel as before. then when i came out from work to ride home, solid as a rock. coming home on the freeway, with no traffic around, i grabbed a handful of front brake and it was like hitting a wall, just like before this happened. what the hell is going on here?!? i'm ase certified in suspension and brakes, and i have no idea on this!! i suppose my master could be bad, but i've never seen a master be bad sometimes, then just fine, that just doesnt make sense. help me out guys, i'm going to the track in a couple week, wanna make sure i'm dialed in. tia.
 

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Chickenstrip Eater
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H2O, in the lines? Hydraulic fluid draws moisture. Is the res lid on tight? Are all the bajo bolts tight and sealed?
 

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The pistons are retracting into the caliper too much at some point, can happen if you get a front wheel shake/tankslapper etc
 

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Possible air pocket in the crossover line??
 

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Discussion Starter #6
i should have added that everything is totally dry, no fluid leaks anywhere. see, if there was air in the lines, it wouldnt get "better" by sitting. i really am stumped here. i will try to bleed it tomorrow morning.
 

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Discussion Starter #7
The pistons are retracting into the caliper too much at some point, can happen if you get a front wheel shake/tankslapper etc
never had anything like a front wheel shake at all. occasional wiggle in the bars, but thats it! i dont think the pistons are retracting as i can still hear the pads dragging slightly on the rotor. also, the level of the fluid doesnt change, it stays right at the upper line.
 

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La Flama Blanca
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I would guess your pistons are sticking on one of your calipers.
 

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Discussion Starter #9
update:

so last night i bled the whole system. my dot5 fluid had changed from a nice deep purple to a slightly-tinted-purple clear. so i bled it all out, couldnt get the lever back at all. zip-tied it to the bar, came out this morning, got no air out of it. rode it to work anyways, the fronts still stop me, but the lever comes to the bar easily. come out of work and the lever is solid as can be. i start riding, and every time i pull on the lever, it gets a little worse. WHAT THE HELL IS GOING ON? do i need to/can i rebuild my master cyl? i dont know what to do... thanks guys.
 

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Judge Dredd Mod
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I'd rebuild the M/C, sounds like the seals are bad. An easy fix.
 

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Dot 5 is a silocone based fluid for show cars and certin applications as it is not hydroscopic and it does not eat paint. Its is NOT better in most applications and is not interchangeable with dot 4(exception dot 5.1) So get some good RBF600 and rebuild you master and i think that will solve your problem.

The proble i think you are having is the seals are swelling up in the master cylinder and causing problems.
 

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I think you'll find that SalKahn (and the fact that your fluid has discoloured in such a short time) is on the right track. Don't use Dot5 fluid - it absorbs moisture. Use the 5.1
 

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Discussion Starter #16
the bottle of dot5 says on it that it is compatible "with all disc and drum brake systems so long as a full system flush is done". so i need to rebuild my master and run 5.1. what is the best 5.1 to use? thanks guys.
 

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Dot 5 is a silocone based fluid for show cars and certin applications as it is not hydroscopic and it does not eat paint. Its is NOT better in most applications and is not interchangeable with dot 4(exception dot 5.1) So get some good RBF600 and rebuild you master and i think that will solve your problem.

The proble i think you are having is the seals are swelling up in the master cylinder and causing problems.
mmmm actually its 'hygroscopic' which means to absorb moisture from humid air.

BD
 

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Lesson in English.

"hygroscopic"
absorbing moisture (as from the air

"hydro·scope"
an optical device for viewing objects below the surface of water.
couldn't have been you!! naaaaaaaaa i didn't think so.:wink:

BD
 
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