about 0-1/3 of the way down the pedal is compeltly normal
once i get past 1/3ish the pedal gets really hard to press, almost feels like i bottomed it out.
at this point the brake pressure stays constant while the pedal is hard.
but if i stand on the pedal and press hard the jeep will also brake harder but the pedal wont have much more movement.
air in the lines?
or brake booster? what do you think?
If you dont get stuck, you're not trying hard enough.
Sounds like a leak in the vacuum booster. If it were air in the lines the pedal would be squishy. I would check your vacuum line running to the booster, but more than likely it would be the diaphragm in the booster that most likely has a leak in it. I'm not sure how to diagnose it but from what you describe that would be my guess.
__________________ DO OR DO NOT... THERE IS NO TRY.
If the pedal is hard to press with the engine running it is the brake booster. If the pedal is soft, you have air in the line.
The brake booster uses vacuum from the engine to help increase pressure on the master cylinder.
Try pushing in the brake pedal right after you turn off the engine. If the pedal is hard to push, it is a bad brake booster and it may have a leak.
I did not read Rubicon2's message before I sent mine. Rubicon2 is right, it is your vacuum brake booster or vacuum hose from the engine to the brake booster. Have someone check the vacuum line, it may have a leak or the brake booster diaphragm could be leaking. Unless you are good at repairing cars and replacing parts, I would recommend you take it to a shop you can trust to do the testing and/or repairs.
They may look the same on the outside but the diaphragm may be larger because of the size and weight of the Cherokee. The push rod leading to the mastercylinder may also be diffrent. When I was in high school I worked part time in the parts department at a Ford dealer. We stocked several diffrent brake boosters. And they were all for Ford cars.
My advice is go online to a aftermarket parts store like Advance Auto or Auto Zone and check prices, it may be cheper to buy a rebuilt. It may also save you a lot of problems in the future.
One thing you don't want to mess with is your brakes!!