Rear brake problems!

Ok so I rebuild my master cylinder, and vacuum bled the system, brakes worked GREAT at the house and even first hour or so of my ride today and now they are gone again unless I pump the pedal.

Any ideas on what else could be wrong?

rebleed, sounds like an air bubble

Bent rotor?

Well I re-bled and there was air bubbles. Bled them the conventional way this time so we will see how that goes. I did about 20 cycles and the last few times no bubbles came out at all.

Ansyder, no bent rotor. I am starting to wish that was the problem!!!

Be sure you crack the banjo bolt loose at the master cylinder hose fitting. It's the high spot in the circuit, and huge bubbles can live there and watch fluid flow back and forth without ever moving the bubble.

I prefer conventional bleeding after vacuum bleeding because I never get a good seal between the caliper and bleeder, seems it sucks air in through the threads. Hope u figure it out!

Will do Gray

So when I push down with my hand on the master cylinder and obviously the brakes are fully engaged if I keep pushing it will force fluid out the bottom. Granted I am pushing hard, but it doesn't seem normal. I am wondering if even after rebuilding the master cylinder if the bore in it is just wore out. Then again the two rubber fitting inside the master cylinder don't seem like they would be hard to get fluid by if you force enough pressure.


If it forces fluid out the bottom, it's not sealing (I know... obvious, right?). Either something wasn't assembled right or the bore's too worn. That's probably where the air is coming from, too.

Ok thanks Gray I will order a new master cylinder.

Ordered an '09 master cylinder for $49.95 off Ebay with free shipping and a mint rear brake pedal....SCORE!

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