Brake Booster Problems -
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post #1 of 4 Old 07-18-2011, 08:10 PM Thread Starter
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1990 XJ Cherokee 
Join Date: Mar 2010
Location: Dothan
Posts: 70
Brake Booster Problems

Hi all,
I have an '88 XJ and I am currently having brake problems that I believe are centered around my booster. When I bought the jeep, the brakes were very soft. I immediately replaced pads/rotors and shoes and installed a new MC. The problem then was the leaking vacuum sound coming from the booster. To remedy this I installed a booster from a '91 parts XJ I have. With this booster installed, the pedal continued to go to the floor and hiss (making the leaking vacuum sound) and would gradually stop the Jeep. Today, I pulled the booster from a '90 in the local pick-n-pull yard. Now my problem is that I have a very VERY stiff pedal, and a very loud hiss from the time the pedal begins to depress. To give you a reference of how hard the pedal is to depress, I am 6'3" and have my seat back all the way and have to brace myself against the seat to actually get the pedal depressed 1-2".

New MC, pads, rotors, shoes.
Original booster: vacuum leak, pedal to the floor.
Second booster: vacuum leak, pedal to the floor.
Third booster: VERY loud vacuum leak, impossibly stiff break pedal.

Has anyone out there had similar problems to this? I have looked at this thing numerous times and there I can't see any possible way that I could have installed this incorrectly, but I am open to any advice you are willing to send my way!


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post #2 of 4 Old 07-19-2011, 10:17 AM Thread Starter
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1990 XJ Cherokee 
Join Date: Mar 2010
Location: Dothan
Posts: 70
Further information:

All these symptoms are with the engine running. With the engine off, the pedal has good resistance. I removed the line from the booster and the vacuum is very sufficient coming from the engine. Is this indicative of a bad booster or could I have some further problem?
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post #3 of 4 Old 07-19-2011, 11:25 AM
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2002 WJ 
Join Date: Sep 2010
Location: Erie
Posts: 322
It sounds like the last booster you put on that gave you the stiff pedal is the only one thats bad.
Did you check you lines? It sounds like you may have a slow leak somewhere.
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post #4 of 4 Old 07-19-2011, 12:24 PM Thread Starter
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1990 XJ Cherokee 
Join Date: Mar 2010
Location: Dothan
Posts: 70
Thanks for your input. The problem I have in wrapping my mind around the other two being good boosters was that when fully depressed, I could hear the vacuum sound coming from the INSIDE of the cab. I am trying to find out if there are any ways to disassemble the booster to test and see if any of the parts inside are replaceable or determine how to localize my problem!
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