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Sudden brake failure

 
  #1  
Old 06-08-2005, 04:51 PM
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Sudden brake failure

86 F250 4X4

I normally had 1 - 1/2" of pedal travel before the brakes started working. Without warning (working right at one stoplight and not working right at the next), the pedal travel distance had increased and the pedal did not return to it's proper height. I can manually pull the brake pedal up and it will hold it's location until the next time I apply the brakes.

No leaks were located and fluid levels are correct. I still have braking power. Pedal is not mushy.

Am I looking at a booster or master cylinder issue?
 
  #2  
Old 06-09-2005, 07:18 PM
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Just a quick follow-up.

The problem was indeed the brake booster.

Not knowing anything about boosters, I did a little reading. Basicly, the booster is a two part chamber. I'll call one chamber #1 and the other #2. Chamber #1 is under constant vacuum. Chamber #2 is either under vaccum or has no vaccum. Prior to any brake application, Chamber 1 and 2 are both in a vacuum condition.

When you brake, air is allowed into #2. The air pressure helps push the master cylinder plunger, assisting you in your braking efforts.

When you release the brake pedal, vaccum is again applied to #2. The two chambers return to a neutral pressure condition and interior springs in the booster push the pedal back into the correct position.
 
 


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