Brake getting ******* their own

It's been two day I have this wierd issue where my brake work just fine, like anything is wrong. But! when I shut off the jeep and come back to it 1 or 2 hours later, the brake pedal is full pressure. I made sure I was releasing the brake pedal before shutting the engine to make sure it's not a problem from me. I also found no leak, no drop in brake oil level, both pad and disk are also pretty new, about 6 to 8 months NAPA premium. No audible noise when driving or when listening to it from the outside with someone pressing the brake. I just can't figure it and never heard of this before.
Any idea?

Does this problem exist while the jeep is running? If not you may have a leaking vacuum accumulator as this will cause you to loose vacuum and have the brake pedal go hard after shutting if off and leaving it sit. That or you could have a slow leak in the booster itself, or the seal where the pedal pushrod goes into the booster. Could be multiple things really, just have to systematically eliminate things one by one.

only happen when the jeep is off for some time...at least 1 hour. Could I find the leak with snoop or something like that?

Is there a one-way check valve in the vacuum hose (inline with the hose). Could be that (if so) the check valve is faulty and allowing the vacuum (within the booster) to escape the booster.

Maybe a bad booster diaphram.......You could sit in the Jeep with the engine running (windows closed).....shut off the engine and listen for a hissing sound coming from where the brake pedal push rod passes thru the firewall.

megatone said:

Is there a one-way check valve in the vacuum hose (inline with the hose). Could be that (if so) the check valve is faulty and allowing the vacuum (within the booster) to escape the booster.

Maybe a bad booster diaphram.......You could sit in the Jeep with the engine running (windows closed).....shut off the engine and listen for a hissing sound coming from where the brake pedal push rod passes thru the firewall.

Click to expand...

wait a minute, now that you are talking about hissing noise. I noticed not long ago when I walk out of the jeep and pass in front of it I can clearly hear a hissing! the puzzle is getting clearer
You guys are all awesome.

Well, the hissing is either air escaping the Jeep, or a snake hiding under the hood, be careful.

Note, the hissing.....if it is coming from the very front of the vehicle could be the sound of the air conditioner system decompressing. Good luck.

megatone said:

Well, the hissing is either air escaping the Jeep, or a snake hiding under the hood, be careful.

Note, the hissing.....if it is coming from the very front of the vehicle could be the sound of the air conditioner system decompressing. Good luck.

Click to expand...

I'll see if I can replicate the hissing with and without AC running.

Haven't spent a lot of time on it today but I took a look at the hose and they look fine...now let's figure a way to find the problem.