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brake problem!!! please help!!!

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brake problem!!! please help!!!

  #1  
Old 12-15-2010, 02:18 AM
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Default brake problem!!! please help!!!

hey guys im new to the audi world i just got a audi a6 2.7t , the brakes dont work at all!!!! when i push the pedal it goes all the way to the floor and doesnt even try to stop, i filled it up with fluid and it didnt change anything, im thinking the master cyl is bad??? if so how hard are they to replace??? any help will be awesome thanx!
 
  #2  
Old 12-15-2010, 02:49 AM
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or possible brake booster????
 
  #3  
Old 12-15-2010, 08:00 AM
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Location: Goodrich, Michigan
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It sounds like the master cylinder but it could be a bad line or caliper. You say you added fluid - was it out of fluid? Or, did you just top it off? Look on the ground under the car and see if there is any evidence of a leak. If you see evidence of a leak, investigate the area around the leak. Brake fluid leaks are usually fairly easy to find. If the fluid is not leaking out and you just topped off the reservoir, then change your MC. I haven't done one on an Audi, but usually they are straightforward.

Good luck,

Bob
 
  #4  
Old 12-15-2010, 08:33 AM
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My first move would be to look for fluid on the ground. If the system is not leaking, bleed the brakes. If this doesn't fix it, change the master cylinder, bench bleeding the cylinder first (some don't need this, refer to the workshop manual) and bleeding the brakes after the install.
 
  #5  
Old 12-15-2010, 10:08 AM
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Just curious -- did the brakes ever work? Why did you buy it with no brakes and how did you get it home?
 
  #6  
Old 12-16-2010, 09:48 PM
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no leaks any where, so it couldnt be the brake booster?
 
  #7  
Old 12-17-2010, 10:43 AM
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No, the brake booster only assists your foot in pushing the pedal. The car will stop without it, it'll just take more leg force. Brakes work on a hydraulic principle. In a nutshell, you push the pedal, the booster assists in pushing the master cylinder. The master cylinder therefore puts a pressure on the system. Fluid pressure through the lines puts a pressure on the calipers to squeeze the brake pads to the rotors. The calipers are essentially pistons that get pushed by the pressure from the master cylinder.

The whole system is sealed. Air does not get in, fluid doesn't get out. Air is compressible, and for this discussion's sake, fluid is not. So if air gets in somehow, it will be compressed, preventing the pistons from moving.

Now, here's where it gets more complex. Brake systems since the 60's have been split. The master cylinder has 2 pistons inside. This is because car manufacturers realized it's too risky to rely on 1. If one line gets a hole in it, you won't lose all braking force. Depending on the car, it splits the system diagonally (one front wheel, one rear wheel) or front-to-back, meaning you'll still stop on either the front or rear brakes. So even if your master cylinder "went bad," it's unlikely that you've lost all braking force. Unless you blew out both seals at the same time, it's highly unlikely. So what has probably happened is a leak developed somewhere, and the MC reservior went dry. Air was introduced into the system, and the brakes no longer work.

Even if you just add fluid, it won't work again because you have to "bleed" the brakes. That means you have to get all the air out of the lines. This is best left to doing a google search, because I could spent a loooong time explaining all the little details. Start by bleeding to get an idea of where you're at. Once that's done, we'll see what happens from there.
 
  #8  
Old 12-17-2010, 12:12 PM
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Location: San Diego
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Default Reverse bleed.

If you suspect air in the lines or booster. Refill by using a system that forces brake fluid up through the bleeder valve. this way all air is forced up the system and out into the resevoir. If this doesn't work / Time for a new booster..
 
  #9  
Old 12-18-2010, 07:24 AM
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No leaks anywhere = master cylinder. As Agreen said, it isn't the booster.

Bob
 
  #10  
Old 12-18-2010, 06:58 PM
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i just bought a master cyl and booster for 45 bucks shipped so i cant beat that deal i will install master cyl and bleed brakes and hope that it works ,lol also how hard is it to change the drivers side axle? as well as where can i get a good one for cheap ??
 

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