Bad Brake Booster?

*2000 XJ 4.0 auto*
Ok guys I’ve been having stiff brakes for about a year now and I decided It was time to address the issue. The booster looks to be the OEM Bosch one so I don’t think it’s been changed before. I realized how bad the brakes were the other day when I was backing a teardrop camper down a hill and I had to literally stand on the brake pedal to get the Jeep to come to a stop.

I’ve done the following tests:

I’ve checked to ensure the booster was getting good manifold vacuum which It seems to (17-18 inches at idle).

I’ve ran the Jeep for a few minutes to build up vacuum and then let the Jeep sit with the engine off for a few minutes and then pulled the check valve out and the booster sounds like it’s holding vacuum good.

I’ve pumped the pedal with the Jeep off and then started the Jeep while pressing the brake pedal and the pedal does “sink” a little and hold.

I’ve let the Jeep run for a few minutes and then shut It off while my foot is on the pedal and during the first 30secs I don’t feel the brake pedal pressing back against me.

I feel like I have no power brakes as if the power assist is absent.

Do you guys think it’s the booster even though It passes the tests?

I feel your pain there. Diagnosing a bad booster is kind of difficult. Two last checks you can do before making a decision. 1) Start the engine and shut it off. Run it only long enough to build vacuum. Pull the vacuum check valve (elbow fitting on the booster) If it 'wooshes' when you pull it off, the diaphragm is at least good (and the check valve). 2) You can also unbolt the master cylinder and slide it forward. If you see brake fluid or rust, change them both.

If it still checks out good, take a look at where the brake pads slide on the knuckles. TJ, YJ, XJ, and ZJ's are all bad about having excessive wear on the slides. The only way to fix it is to grind the spot out and fill it with weld, then grind it smooth and square again. It can cause calipers to bind, so give it a look.