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XJ Brake HISS

jeepsrock

NAXJA Forum User
Location
LA California
I have a 94 XJ with the 4.0 Engine. This has been happening for about 2-3 yrs and pretty much stayed the same and i was wodering if this is normal. In the morning when i press on the brakes firmly i hear this hissing noise. On the road it drives and brakes fine unless i press firmly where the brakes almost reach their max i hear this hiss from under the dash. I am not really sure if this is normal or not, but its been like this for a while and everything works fine ???

pete
 
xray said:
It sounds like it might be vacume brake booster.

Check around the Master Cylinder,if you see signs of leakage,then there is the possibility the diaphgram has been screwed.
Brake fluid and the diaphgram do not play well together...
 
Ok folks i further analysed the probelm by performing the brake pressure test described in my service manual. I shut off the engine pressed the brake pedal until it got hard and then kept my foot on it and started the car , the pedal went down as it should but as it got to last few cm it hissed a bit. Never the less the brakes still work but my braking power has seemed to become less and it takes me longer to brake and for me to push harder. The hiss seems to be coming from the where thepedal atatches to the firewall and is audible in the hood compartment also.

I am open to sugeestions.

pete
 
Its a leaky vacuum booster. Not bad enough to have the brakes not work, but not a system I would want to bet my life on.
 
Had the same thing in my 89 trailrig/DD-at the time. Caused some concern with the passengers (LOL @ Hunter) but the pig stopped fine. A new booster fixed it.
 
Well I had the same problem with my 87 Laredo, and I have replaced everything in the entire brake system except the proportioning valve. I have gotten used to it over the years and the car still stops fine. I have replaced the brake booster but the sound is still there. I just ignore it now...
 
All good info...Will bleeding the system help or should i just cut the chase and replace the vacuum booster ?

I have a junked 93 xj in my back yard, would its booster fit in my 94 xj ? Once i take it off the junked xj what can i do to make sure if its working other than install it in my XJ and waste time?

And whats involved in replacing my booster ?

thx
pete
 
I pulled the booster off my junked 93 xj and was wondering if there is anything i can do to test it while its off the jeep so when i put it back in my 94xj it wont be double work ?

pete
 
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