Front brake issue kx250

[fatdaddy]

Hey guys...last week in a HS my son's front brakes siezed up...luckily I was close with tools and took front caliper off to allow him to finish lol...i rebuilt both figuring that would solve it...the boy took went out today and the same thing happened again...im drawing a blank now....would you guys lean more towards cylinder or caliper for being the culprit

[Foxx4Beaver]

When you rebuilt the caliper...did you completely tear it down, and remove the piston(s) and inspect them too?...almost
sounds like a piston might be sticking.

When you say you "rebuilt both", are you referring to rebuilding the master cylinder as well?
You could possibly have a bad brake hose/line too. For the most part, brake hoses are interchangeable, so if you have another bike, you could swap hoses and try that, before spending the money for a new one...providing the one you swap out has enough slack in it, or is at least as long as the one on the bike now.

[sandblaster]

Foxx is right.
I see many brake systems that have sticky pistons.
In your service manual it recommends that you disassemble, clean, and inspect at regular intervals.
Few ever do.
What happens is you will build up goo between the two piston seals in each piston.
Then the piston tries to slide past that goo and it gets stuck.
I blow the pistons out with air, clean everything exceptionally well and pay close attention to cleaning the seals.
Your wife's tooth brush is excellent for cleaning seals.
Use a lint free rag.
Assemble with a little brake fluid.
It's amazing the difference it makes.

[sandblaster]

[Foxx4Beaver]

Your wife's tooth brush is excellent for cleaning seals.

Hahahaaaaaaa!! that's awesome!...thanks 'Blaster, I needed that laugh.

[fatdaddy]

When you rebuilt the caliper...did you completely tear it down, and remove the piston(s) and inspect them too?...almost
sounds like a piston might be sticking.

When you say you "rebuilt both", are you referring to rebuilding the master cylinder as well?
You could possibly have a bad brake hose/line too. For the most part, brake hoses are interchangeable, so if you have another bike, you could swap hoses and try that, before spending the money for a new one...providing the one you swap out has enough slack in it, or is at least as long as the one on the bike now.

Yes, I rebuilt both the caliper and the mc....and, used a different brake line also. That's why I'm pulling a blank on this.

[fatdaddy]

Foxx is right.
I see many brake systems that have sticky pistons.
In your service manual it recommends that you disassemble, clean, and inspect at regular intervals.
Few ever do.
What happens is you will build up goo between the two piston seals in each piston.
Then the piston tries to slide past that goo and it gets stuck.
I blow the pistons out with air, clean everything exceptionally well and pay close attention to cleaning the seals.
Your wife's tooth brush is excellent for cleaning seals.
Use a lint free rag.
Assemble with a little brake fluid.
It's amazing the difference it makes.

During rebuilding I pulled everything apart inspected ,cleaned thoroughly just like in the pics and in stalled New seals....figured this would've solved the issue....but no. This is why I'm perplexed...and as I explained to Foxx I even used a different brake line.

[sandblaster]

Have you put the bike on a stand, spun the wheel, and watched the brake rotor?

[fatdaddy]

Have you put the bike on a stand, spun the wheel, and watched the brake rotor?

yea, rotor is good....today I robbed the front brake assembly off my 96kx250 and put that on the 98...pulled everything back apart, mc and caliper reinspected, cleaned and installed on the 96 everything looked good and seemingly worked fine...took the bikes out this fternoon and same thing happened within 20 mins!! So ima frustrated!

[Heniz]

Have you put the bike on a stand, spun the wheel, and watched the brake rotor?

yea, rotor is good....today I robbed the front brake assembly off my 96kx250 and put that on the 98...pulled everything back apart, mc and caliper reinspected, cleaned and installed on the 96 everything looked good and seemingly worked fine...took the bikes out this fternoon and same thing happened within 20 mins!! So ima frustrated!

What brake fluid are you using and what material type are the seals?

[fatdaddy]

Have you put the bike on a stand, spun the wheel, and watched the brake rotor?

yea, rotor is good....today I robbed the front brake assembly off my 96kx250 and put that on the 98...pulled everything back apart, mc and caliper reinspected, cleaned and installed on the 96 everything looked good and seemingly worked fine...took the bikes out this fternoon and same thing happened within 20 mins!! So ima frustrated!

What brake fluid are you using and what material type are the seals?

hey there thanks for reply...im using dot4 and seal material is (assumingly) rubber...thats what they appear to be. Brand of seals is ProX

[Foxx4Beaver]

just by chance, did your son crash somewhere, that may have caused damage...like a bent carrier, or crushed brake hose.
a brake hose that collapses will cause a sticking caliper too...it happens on cars/trucks more often than you think.