I recently finished converting my 91 Cherokee from the abs system that barely worked to a standard non abs booster and master cylinder. It sat a while after swapping it out due to a motor swap and once I got the thing running it had no brake pressure and the peddle would go to the floor. I bled the brakes multiple times and even went to a shop my buddy works at to have it done there so I can also inspect everything while it was on a lift and still no luck. I adjusted the pushrod length on the booster and that didn't help either. I then adjusted my rear drums and I had great brake pressure and everything was working great! But i noticed the front calipers were too tight due to the adjusted push rod and the moment I put any weight on the peddle the brakes would grab pretty hard. So I shortened the pushrod again and I had lost my brakes again. So I set the pushrod to what I thought was the proper length and made sure the drums were set right and I can't seem to get the brake pressure back. Any ideas? Thing thing has sat for 2 years and I've been wanting to drive it and winter is coming up so I'd like my 4x4 running again.

 

I would change the master cylinder if the you had sat on the jeep for 2 years with air in it I would think the seals would dry out .

 

I ended up replacing both booster and master because I thought the same thing

 

It may be an issue with the proportioning valve sticking, I believe they can be taken apart and cleaned