I am back at the brakes again. have not driven the XJ since October. My DD is a 1993 Toyota pickup so the XJ is my toy.
I removed the booster yesterday and took a good look at it. It appear as if it is not user serviceable. I wish it was. The price of a remanufactured one at the auto parts places here in Jacksonville, FL is over $80. About the same price as Summit Racing and other online stores. From the local Pick-Your-Part is $25 +/- and an $8.00 core. There are plenty of ZJ, WJ and Explorers at the yards and to the untrained eye ( booster installed) they all look the same. Would one from a WJ work with no modifications?
Looking back at the booster I just removed, it is not obvious as to what caused the hard pedal. I would however point my finger at the atmospheric inlet valve assembly. According to my workshop manual, there should be a filter there ( where the rod from the pedal go into the booster). On my XJ, it have completely disintegrated and probably got sucked into the rear diaphragm housing. The manual also said it depended upon the difference between atmospheric pressure and vacuum to operate properly. This booster have no leaks as far as I can tell It is just hard to push almost as if the booster is not working.