booster leak?

ok the other day when i stoped at a light i noticed this hissing sound coming from the fire wall well when i moved my fot a little it went away. it seems to only happen at certain locations on the stroke it stops just fine but iam not liking this sound any one else have this happen to you?

could be as simple as the grommet that holds the check valve is leaking or the check valve went bad.

man that sucks. i had the exact same thing happen to my "89 a few weeks back. it seemed that it was always hissing unless the pedal was pressed. also, the booster pump would come on for what seemed like forever at startup. this lead me to believe that a severe leak was somewhere. i used a stethescope to narrow it down to inside the master cylinder itself. i decided to risk tearing it apart myself. at the dealer, a new m.c. cost $289 while the rebuild kit was $209. after a lot of work, i got the m.c. out. i pulled the piston assembly out and discovered that the two teflon rings that seal the piston were frayed. when you looked at the real closely, you could tell that there were high spots where the teflon had somehow folded itself over. this caused a slight gap. i just got a razor and trimmed the high spots off and reassembled. now my breaks work better than ever. now more hissing and the pump only runs occasionally. i wouldn't recommend doing this unless you consider yourself a competent mechanic. doing repairs such as this to the brake system are very dangerous and should only be done if you are absolutely sure of yourself. also, plan to do it on a weekend so you have plenty of time. also make sure you have plenty of fresh brake fluid. you will lose quite a bit in the process. other than that, good luck!

Man, I have this same problem. At least I am not the only guy in the boat. I think i will try to live with it until next summer, and drop in the later model booster. Cheers.

Before you go so far as to change out the booster, check both the grommet in the fact (where the vacuum hose connects) and the nylon elbow that goes into the grommet - I have known both to fail at times. An actual failure of the booster itself is agreeably rare, in my experience.

Both parts should be farily cheap from any shop that stocks the MotorMite HELP! line - and they're a lot easier to change out than the entire booster. If they don't work, keep them for spares when you change the booster afterwards...

5-90

i think i'll do the same as cherokee 89 and install a newer booster next summer ( that way i'll be one step closer to rear disk brakes) thanks for you input.