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Brakes spongy

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Ok I have a 2013 KX450F.  I put a Tusk oversize rotor on it and it was spongy so I put new honda pads on it and it felt good then got spongy.  I bled them and same thing, I just put on a master cylinder rebuild kit and it's still spongy, if not even worse.  By spongy I mean you have to use about half of the lever travel for it to grab.  It seems to grab good like every few pulls but then it gets spongy.  think its the caliper needs rebuilding?  Can you even rebuild a caliper?  I have the same master cylinder on my 2011 RMZ450 (well it has the same number on it) and that thing grabs with hardly any pull to it.

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Yeah its not the rotors or pads, it doesn't even really engage till your half way on the lever.  Well I fillled and kept cap off and left bleeder open and let it get low, then refilled a few times.  I then filled, put cap on, squeezed brake lever and opened bleeder, tightened bleeder, and pumped back up.  did that a few times then refilled and did that till no air came out.

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Try a steel brake line. And bleed it a lot with a good quality brake fluid

I run galfer 270mm front rotor kit with a ride eng. brake line and super blue brake fluid... My front brakes are really really good. And make sure you bed in the pads correctly

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Going by your description of bleeding, I guess your front system still has air in there.  Search for more info on front brake bleeding technique.

 

If yours was firm, and then went mushy again, then I'd suspect a fault. But get all the air out and lever firm before considering anything else.

 

I draw fluid out of the calliper bleed using a syringe with connection tube. Careful to maintain vacuum on the lower bleed. So I pull air out of the bottom while refilling and pumping the top.  On the upper/lever end I ensure the brake line has a clear path continuously up to the bleed hole, so air can propagate all the way up and out. Gravity doing the work up there.

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I bled the hell outta that thing and it still does it.  Its wierd cause it will feel nice and firm on two pulls then the third pull goes spongy.  then do it again.  It's not always two and third but it will feel good on some pulls then go spongy.  And I did several syringe methods so I know there isn't any air in it.

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In that case (initially firm and bled), then it sure could be faulty. Weird though because you said you rebuilt the master, and if the calliper cannot hold pressure then I'd expect fluid to leak out of it. So maybe your master rebuild kit aint doing the job.

 

You could try adjusting the lever/piston position screw on the master, in case some port isn't being open/shut correctly. Then re-bleed.  Total guess.

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Well swappd master cylinders with my 2011 rmz450 and wow do brakes work now. So idk what happened there really isnt much in there to go bad

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Well swappd master cylinders with my 2011 rmz450 and wow do brakes work now. So idk what happened there really isnt much in there to go bad

did you happen to take your old master cylinder apart and check to see if you put the seals ok correctly? Did you notice if the piston was rubbing the master cylinder housing? Only reason I ask is I am having the exact same issue. My girlfriends KX85 front brake lever was spongy, I bleed it and saw some dirty fluid come out, so I rebuild the master cylinder, assembled it, bleed the lines and had the same issue you had. I was stumped so I took a look at the caliper itself and noticed when I pulled the lever 1 piston moved better then the other. The piston that was slower/stiff the dust seal was pinching (see photo) so I ordered new fluid seals and dust seals with a tusk stainless front line. Parts should be here tomorrow. Hopping that is the fix, if not I might yank the master off my KX250F and see if that makes it better. Just seeing how you made out ImageUploadedByThumper Talk1398888109.107013.jpg

2006 KX85 / 2012 KX250F

2012 KX450F / District 6 #225

Instagram + Twitter: Schearer225

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I didn't pull back apart. I rebuilt it, I'm kind of wondering if I put the two seals in backwards. I mean that's the only thing I'm the system that could be messed up.

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I didn't pull back apart. I rebuilt it, I'm kind of wondering if I put the two seals in backwards. I mean that's the only thing I'm the system that could be messed up.

Yeah that's kind if what I was thinking maybe I did wrong, but not really sure. UPS better hurry up and get here so I can figure it out lol

2006 KX85 / 2012 KX250F

2012 KX450F / District 6 #225

Instagram + Twitter: Schearer225

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Well just a follow up on my similar braking issues. Just a quick recap:

Bike is a KX85, brakes were supper spongy and lever almost went to the bar. Decided to get a All Balls master cylinder rebuilt kit. Cleaned everything perfect and rebuild the cylinder. Noticed some slight rubbing with the piston and the master cylinder housing. Smoothed it out with 1500 grit sand paper. Bleed the brakes like crazy, still had a good 2" pull till it stopped the wheel.

Look into the caliper and saw 1 piston seemed to be hanging up and a dust seal seemed to be pushing out. Ordered new fluid and dust seals for the master cylinder and tusk brake pads, and tusk SS line. Rebuild the caliper clean as a whistle and bleed it like crazy.... Slight better but still feel like crap. WTF.....

Decided to swap master cylinders with my 2012 KX250F since it's the same part number in the housings. Feeling a little adventurous since both were off the bike and on my table, took the KX250 piston out to compare...BOOM. Rookie move, I rebuild the KX85 one with the cup seals BACKWARDS. felt kind of like a dummie, but in my defense they go on kind of strange, the seals are coned shaped a bit, and you actually have the cone shape going the opposite way of piston travel if that makes sense.

So I flipped the seals around, buttoned it all back up bleed the puss out of it and I would say it's MUCH better, but in comparison it takes 3/4" lever pull to make a full stop spinning on the stand and my KX250 and KX450 take 1/2" to get the same amount of grab. I know it's only a 1/4" difference but it kind of bothers me. It COULD maybe be the pads are actually not beaded in yet since they are brand new and all the testing has been while the wheel is spinning on the stand, and the rotor and pads are technically smaller then the 250 and 450. Going to have the girlfriend keep a eye on it when she rides this weekend and hopefully it gets better once the pads bead in. Hopefully that long story helps anyone else in a similar situation. Ride on my Brotha's!!!!

2006 KX85 / 2012 KX250F

2012 KX450F / District 6 #225

Instagram + Twitter: Schearer225

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Try this, zip tie the brake all the way to the grip so that it is fully compressed and leave it overnight. It should push all the small bubbles up. Its worth a shot

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