Brake booster ?..... or something else?

Well I think I lost a brake booster today.... brake pedal doesn't have as much travel, is hard to push & theres a hissing sound up under the dash at the rubber boot going through the fire wall (it sounds like theres one PISSED off snake up in there) engine RPMs rise alittle when I press the pedal. Is there some hidden vac. lines that aren't that noticeable or something else to look into? Is there any better one to get or just a NAPA or A.Z. one and R&R it?
This is on a 96 with an 4.0 & a AW-4 around 106K.
Thanks for any insight....
Curt (aka Xtreme XJ)

It sounds like the classic booster diaphram. Replacement is your best bet. I've had good luck with the NAPA ones.

There is a site,Mad xj.com (I think) there is a write up w/pics.
Basically what it says is that you can replace pre 92' boosters w/booster and master cyl from 95' and improve your braking over the original set up.
Evidently the Bendix set up is known for failure or poor braking.
Think this is the right addy,if not you can do a search...
madxj.com

I just swapped in a new booster for my '92. Purchased it from Peb Boys for $99. It came unpainted so I had to rattle-can it prior to installation. It works great except... The rod connecting the brake pedal to the booster unit was 4 1/2" on the replacement and 5" on the old one. Jeep still stops but the pedal is closer to the floor and doesn't engage the brake light switch. I had to hose clamp a small bit of metal to the pedal arm so the the brake light switch is properly actuated.

Be sure to check the length of both the rod to the master cylinder and also the rod to the brake pedal to be sure that they match with the lengths on the booster you are removing. Sorry, I can't tell you what to tell the autoparts counter person so that the correct booster arrives. I gave them the usual info. Trouble is that Pep Boys had to special order the booster so I couldn't just do an immediate comparison. You might be able to measure the brake pedal rod length without removing the booster and be able then to check the replacement when it arrives at the parts supplier. Mostly you'll just have to take your chances.

Thanks for all the help guys....ordered a NAPA unit this A.M.
Curt (aka Xtreme XJ)

This is sort of late, but will hopefully help anyone searching on this thread. On my '96 non-ABS, the oem booster setup had a 1/2" aluminum spacer that shortened the rod connecting to the brake pedal by that much. With the after market booster from Napa, the brake pedal did not push the brake-light-off button because the rod was 1/2" too short. Do not install the after market booster with the spacer, at least remanufactured ones from Napa auto parts. I did and had to redo the whole installation just to remove the spacer. Once the spacer was removed, the brake pedal kept the brake light off until pressed for stopping and all was fine.