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Old 02-22-2010, 05:21 AM   #1
dniweR
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Default Rear Brakes Wont Work

Hello all,
First post, and hopefully many more to come.

Finally upgraded from my old bike today, bought the new one off eBay, and it had no mention of brake troubles - go figure. And partially my stupidity for not sussing it out before hand.
Anyways here's the problem, and what I have tried to do. Its probably really simple, but I havent had any experience with hydraulic brakes.

When I push the foot pedal down, there is nothing - no resistance at all. straight to the bottom.

Have tried to bleed, air isnt getting to that end, so I take off the master cylinder. There's fluid in there. Max level. give it a pump with my hand, slight amount of air comes out, but maybe only a drop of fluid. Put my finger over the end where the hose screws in, and a small amount of air pressure is there, but I dont know how much there should be.

I put it all back together, and pump for about 30 mins. No fluid is circulating to the caliper end of the system, not even a build up of air, still the pedal goes to the floor. No pressure.

What could this be? What have I missed?

There doesnt appear to be any leaks, but then again, the fluid isnt going through the tubes to the caliper end.
Have done a fair whack of research on this, but most people seem to be able to get it fixed with some bleeding, or adding fluid to the cylinder where the thread is.

Any help would be awesome. I'm a little dissappointed getting a bike that I cant ride yet.
Do I need a new cylinder? Are they fairly cheap, or universal?
Cheers
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Old 02-22-2010, 06:32 AM   #2
seruzawa
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You probably need a new piston kit for that cylinder. Maybe a new cylinder. Both should be available from a dealer or an internet parts source like bikebandit. Better get a service manual while you are at it.

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Old 02-22-2010, 08:23 AM   #3
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I'd still ride it, you shouldn't be relying on the rear brake anyway. As Dr Saruzawa said you need a rebuild kit if available or a new rear master cylinder if not. The piston or seal is most likely bad. Sometimes you can take the top off the fluid reservoir and see if there's any air bleeding back in when you pump the brake which may indicate a loose fitting bleed screw, but you probably need to rebuild or replace the master cylinder. What make and model bike is it?
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Old 02-22-2010, 08:33 AM   #4
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How are you bleeding the brake? Rear brakes can be tricky compared to fronts.

The best way to bleed is with a clear tube attached to the caliper bleed valve. Put the tube on the valve and then insert the other end in a small clean jar or bottle with enough fluid at the bottom to cover the end of the tube. Open the bleed valve and begin pumping the lever. You should see fluid moving through the tube, probably with bubbles. Once there is clean fluid only in the tube, close the bleed valve and you should be good to go.
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Old 02-22-2010, 10:34 AM   #5
pushrod
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Okay, I'll ask -

What kind/year bike is it?

Where are you located (U.S./Laos/Nigeria).

Tech tip: See if there are pads (assuming it's a disc brake) installed, and what condition they are in.

Giving the PO the benefit of the doubt, they had the rear wheel off for some reason; the pads are fully retracted, and there is air in the line.
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Old 02-22-2010, 10:58 AM   #6
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Sounds like he doesn't realize how long it takes to bleed brakes after you let air into the system. My guess is he doesn't need any parts. Good luck!
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Old 02-22-2010, 06:39 PM   #7
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Drag your feet.
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