Discovery I Brake Issue - Defender Source
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  #1  
Old August 1st, 2011, 07:45 AM
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Discovery I Brake Issue

Hi Guys, I dont know if thi is the right place to put tis but, anyway, here goes;

Seems there is an issue with my Discover I 94' brake master cyl or brake (servo) booster. Pedal goes to the floor with no brakes. Pedal will pump up some what but really no braking. No leaks, fluid level is fine. My Question is; Is there any sure fire way to test if the brake booseter has failed without tearing things apart? In another post I read what sounded like a test where you disconnect the vacuum line to the booster and if the pedal is a little firmer to push then it's the brake booster at fault. Is this correct? Is this the only test? Any other ideas?

Mark
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  #2  
Old August 1st, 2011, 09:41 AM
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Quote:
Originally Posted by Mark McDonough View Post
Hi Guys, I dont know if thi is the right place to put tis but, anyway, here goes;

Seems there is an issue with my Discover I 94' brake master cyl or brake (servo) booster. Pedal goes to the floor with no brakes. Pedal will pump up some what but really no braking. No leaks, fluid level is fine. My Question is; Is there any sure fire way to test if the brake booseter has failed without tearing things apart? In another post I read what sounded like a test where you disconnect the vacuum line to the booster and if the pedal is a little firmer to push then it's the brake booster at fault. Is this correct? Is this the only test? Any other ideas?

Mark
If it's going to the floor, with no brakes, and pumping it up gets you pressure again..... it's the master.

If the booster fails the pedal gets much harder to press but you still have brakes. It just assists but you can stop without it. No need to disconnect the vacuum line to do that test, just press the brakes with the engine turned off.... same thing. If the booster is good, it SHOULD get much harder to press the brakes without any vacuum.

-Hans
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  #3  
Old August 1st, 2011, 09:51 AM
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Discovery I Brake Issue

Thanks Hans,

So the Master fails as in I should see fluid leaking from someplace? or do you think the thing is worn internally (268K miles) to the point of just not pushing any fluid to the wheels? No visible signs of leaks anywhere, inlcluding at the resiviour mounts.

Mark
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Old August 1st, 2011, 10:02 AM
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Have you tried bleeding the system?
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  #5  
Old August 1st, 2011, 10:06 AM
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Discovery I Brake Issue

Hi Pedro,

No, havnt bled the system yet. Would the need to bleed the system just happen? I could see the need to bleed the system if some past of the system had been opened up recently for some reason but all of a sudden this issue set it.

Mark
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Old August 1st, 2011, 10:12 AM
The Dro
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Hey Mark,

If the system has air in it you'll have no pressure at the pedal. The pedal will go to the floor with no resistance.

It's a fairly simple and free way to check for issues. Just need a "pedal pusher", while you get dirty.

You might have a bad line seeping air.

Then again, it might be something different... just trying to avoid you changing parts you don't need to change (been there, done that)
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  #7  
Old August 1st, 2011, 10:15 AM
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Thanks Pedro, I'll check that too!

Mark
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  #8  
Old August 1st, 2011, 10:24 AM
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Hey Mark,

Just pulled this out of the RAVE book.

P
Attached Files
File Type: pdf wmlj970e 604.pdf (8.0 KB, 90 views)
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  #9  
Old August 1st, 2011, 10:27 AM
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Thanks Pedro,

Very helpful! I'll check this out.

Mark
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