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Vacuum problem=soft brakes

Mr.Shrek

NAXJA Forum User
Location
Murfreesboro, TN
So I've tracked down my soft brakes and brake light issue (dash light that is) to the vacuum lines and canister. I pull the line from the m/c @ the intake manifold and there is a vacuum. I pull the small line coming from the vacuum canister on the top front of the intake manifold and there is vacuum there. I pull the line going into the neck of my air box and there is nothing. I pull the 2 lines at the vacuum canister (small line coming from intake manifold and larger line coming from air box) and there is nothing. Where should I be getting a vacuum if not at all of these points and what would be the cause of this? BTW this is on a 91 XJ with the 4.0 motor. Thanks for your help.
 
Sounds like you are looking in the wrong place. The easiest way to check for brake booster operation is this: With the engine off pump the brake pedal 5 or 6 times until the pedal is hard to press. While holding down the brake pedal, start the engine and see if the pedal moves down. If it drops an inch or more then your booster is working just fine.

No vacuum = hard brake pedal.
 
Ok I just gave that a shot. No increase in pressure as I pump the brake pedal and once I start the engine the pedal does not drop down. So I take it I have a bad brake booster. Thanks for the help. I should have put a question mark at the end of my thread title.
 
Ok I just gave that a shot. No increase in pressure as I pump the brake pedal and once I start the engine the pedal does not drop down. So I take it I have a bad brake booster. Thanks for the help. I should have put a question mark at the end of my thread title.

As long as your vacuum supply to the booster is good, then yes your booster is not working.
 
And from when I pulled the hose from the booster at the intake manifold the vacuum was strong. Tomorrow I'll pull the other end at the booster to make sure there isnt' a clog in the line and go from there. Thank you for the help.
 
And from when I pulled the hose from the booster at the intake manifold the vacuum was strong. Tomorrow I'll pull the other end at the booster to make sure there isnt' a clog in the line and go from there. Thank you for the help.

Be sure to test the check valve too. It is the fitting that the vacuum line attaches to at the booster. Pull it out of the booster and make sure the vacuum is getting through it. You can test the one way valve by trying to blow through it, it should flow free in one direction and not flow at all in the other direction.

Good luck.
 
The line and check valve both checked out fine yesterday. So looks like you were right on the brake booster being shot. I'm now looking to go ahead and do the WJ swap. Thanks for the help.
 
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