4 door 87 Cherokee with 4.0L and 5 speed. Bought it 2 weeks ago.
Backing out of my moms driveway I pulled it out of revers and pressed the brakes to stop and the pedal went to the floor and it keep rolling down hill. Before I could slam it into 1st and power forward I rolled backward into a tree. Luckily I hit the tree dead center in the bumper witch ended up hitting the trailer hitch and stopped the tree from hitting the hatch.

Checked the master cylinder reservoir and it was full. I got under it to look for a brake leak and found nothing. Lines are all intact calipers are all dry and no brake fluid coming from drums. With the Jeep on or off the pedal has zero resistance and just goes to the floor with no effort. It also comes back up slowly. (Video below)

I noticed the 2nd day I had it there was a vacuum sucking sound coming from under the dash and it changes sound when you press the brake pedal but the brake felt ok a little stiff but they worked fine.

I'm thinking its the master cylinder but I also noticed it pulling to the driver side vary little while driving and pulls harder to the driver side under braking. Also after driving it the drivers side wheel feels much hotter than the passenger side wheel. So it could posable be a blown caliper but like I said there is no brake fluid leaking.

Click video below


I just wanted to hear from some other people on what they thought it could be before I start throwing money at it.

Thanks

 

Sounds to me like air in the lines. Did you try bleeding it?