it wont go into 4wheel drive its an automatic shifter in the floor
there may be a hole, or crack in the vacuum system, in my Jimmy (nearly identical vehicles), i had to get out and manually close the valve, after shifting inside the cab. it would then stay in 4-wheel, until i disengaged it (in the cab) if you can locate the piston, give it a try. for the jimmy, it was just to the passenger side of the engine, behind the battery. Start your engine, engage 4-wheel, hop out, then squeeze that piston closed - if it stays closed, then your problem will be the same as mine. if so, get these hoses fixed as soon as possible - when one hose starts wearing out, the others are usually right behind it. this can mean future serious problems, if your bronco is an automatic.
Search Ford Bronco II Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford Bronco II Experts