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I have a 2001 Scrambler 500 4x4. New right front caliper, rebuilt left front, and new pads on front and rear. I have been trying to bleed brakes. I'm using a vacuum bleeder and tried reverse bleeding, with a syringe. I have used over 3 large bottles of brake fluid. The hand brake lever is fairly firm and brakes will only slow the machine. I can't get enough pressure to lock up wheels. I can hold brake lever and still spin wheels by hand, with some resistance. I've not done anything with the foot pedal because it has never worked anyways. I can see no leaks in the system. What am I missing? Thanks for the help!
 

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Had the same issue. The rear brake is part of the braking "system". You need to bleed the rear brake caliper. I have been using the $24 Harbor Frieght vacuum system so I bled both rear nipples and voila- nice firm brakes. On the plus side - you now have pristine brake fluid in the front calipers. BTW It took me about 6oz. to flush out the rear caliper. Hope this helps. Dom
 

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Thanks for the reply! I have bled the rear caliper. I actually plugged the inlet from the foot brake on the rear caliper. I get an enormous amount of air bubbles from all 3 calipers. I can't believe that much air could be in that small of a system. My vacuum pump will hold pressure until I crack the bleeder, so I'm pretty sure it's not bad. I've bled many car brake systems, and never had this problem. I can't figure out how it can be sucking so much air into the system, when I see no leaks. The master cylinder reservoir doesn't lose any fluid. The only part I haven't messed with, is the master cylinder. Is it possible for it to suck in air, and not leak fluid?
 

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Is it possible for it to suck in air, and not leak fluid?
Absolutely - the MC piston has two seals - one seal traps fluid in the system and generates the pressure that operates the brakes - the other seal is responsible for releasing air from the system into the MC and replacing the air with fluid - if the second seal is drawing air instead of fluid (air is easier to draw than fluid), then it will constantly add air to the pressure side instead of fluid. Not as common is a caliper seal sealing against fluid, but allowing air to enter when the pressure is removed.
 
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