Brake Failure! Help

Hi everyone.
Today I experienced brake failure on my way to class. I was driving and as I steped on the brake pedal, the pedal went almost to the floor, but there was still a little brake power left, enough to stop the car but not nearly as it should. The pedal felt soft and "spongy". Also the brake light came on! I also noticed a hissing noise when I step on the brake, as if air was leaking from somewhere. The noise has been there before but the brake still worked fine.
Another problem I had before this was that when I steped on the brake a little harder, the left rear wheel locked That one I didn't understand since it started suddenly!
Has anyone heard or had similar problems?
Any suggestions on how to fix it?

Thanks for your help.

Nick

The hissing sounds like a bad power brake booster. The low pedal MAY be (not guaranteed) a master cylinder leak.

Start by removing the master cylinder from the booster, and look for leaks where the master cyl. attached to the booster. ANY LEAKAGE means you need a new master cyl., and the hissing, of course, means it's time for a new booster.

A bad booster probably would not cause a low peddle, it would cause a hard peddle. And I don't think it would trigger a warning light.

It sounds like you lost the hydraulics on either the front or the rear. Open the master cylinder and see if one chamber is empty. If so, follow the line from that chamber and determine if it goes to the front or rear. Then inspect EVERYTHING associated with that circuit to determine what leaked.

When that happened to me in the '88 XJ, the hard line feeding the rear rusted through and popped just about under the driver's seat. I spliced in a short patch, had a friend come over to press the peddle while I bled the rear brakes, and it popped again a foot away from my repair while we were bleeding it.

BTW, Nick --

There are many variations among years and models. In the future, it would help people answer your questions if you include what year your XJ is, and where appropriate what equipment. (For brakes, it doesn't matter what engine or tranny, but for other questions it could make a big difference. What would potantially matter in your case is the year and whether or not you have ABS.))