Brake pedal sinks on rear hydro...

[Joe460]

I have an 03 blaster and I have a problem with the rear brake. Every time I press down on the pedal it slowly sinks to the bottom. There are no external leaks and the fluid stays at the right level, so I think that an o-ring is worn out in the master cylinder.
What do you guys think is wrong and how should I go about fixing it? :-/ (hopefully without replacing the MC)

 

[R&S Polishing]

check your fittings air is getting in or you already have air bubbles stuck in the line. use a vacuum bleeder they are vast and easy to use can pick one up at harbor frieght for less that $20 dont spend the hour it takes to bleed it manualy it sucks been their done that! thats why i have a vacuum pump bleeder.

 

[Awk08]

yeah, i'd give re-bleeding them a try also, i've found bleeding them with the cap off the rezzie makes it go much faster when doing it manually, and watch for fluid leaking while doing that,
how's the rear pads ?? possibly time for new ones ??

 

[sheeblast]

it doesn't take an hour to manually bleed the rear brakes.
i put a new line on and had mine good within 10 minutes.
but like awk said, bleed and check pads.

 

[Awk08]

making my gsxr kits that i sell has gotten me pretty good at bleeding brakes, and have found having the rezzie cap off helps a ton, and also having the caliper off and up higher than the master, so any air can flow up and out, with the bleeder(s) facing upwards also helps,when doing this off the disc be sure to put something in between the pads so they dont close tighter than the disc, i usually use my 10mm speedwrench, they can be a biotch to get back open without damaging the pads
but sometimes it does take a little while, other times 5 minutes

 

[super noober]

I have an 03 blaster and I have a problem with the rear brake. Every time I press down on the pedal it slowly sinks to the bottom. There are no external leaks and the fluid stays at the right level, so I think that an o-ring is worn out in the master cylinder.
What do you guys think is wrong and how should I go about fixing it? :-/ (hopefully without replacing the MC)

does it build pressure at all? i had this happen with my front brakes and it was a problem with the master cylinder.

 

[royalt67]

Air in the lines would make it feel mushy, but a slow sinking pedal is definitely a master cylinder, internal leak past the piston seals. Replace and bleed.

 

[Joe460]

Pads are good, and every time I bleed it, it still sinks.
If it is a problem with the master cylinder, should I replace the whole thing or just the seals?

 

[Awk08]

just a rebuild kit will do the job

 

[royalt67]

Sure a rebuid kit will do (probably) but it will never be as good as a new one, and do you have a hone for that small of a cylinder?