'87 Subaru GL Turbo Wagon 4wd with push button switch on shifter.The 4wd will not engage when button is pushed in.
are you diving on ICE or snow or offroad.?
is this the first time ever to use 4wd and not read the users guide
when not to use 4wd?
the last 87 Subaru running, sure
4wd has many meanings, AWD, or part-time or Full-time or a mix.
most old cars are just part time, like ww2 jeeps are and were then.
and they do not all work the same way.
1987 specs are cars is not easy to find.
the users guide warns of using 4wd in turns, steering fights you.
so that tells me it is part-time 4wd, not for pavement. Not real AWD.
the 4wd shift mech, is vacuum servo operated and I say all that is bad 35 years old , vacuum parts cracked diaphragms.
some have sol called full time rear axle with clutch skip device option.
buy the old paper, shop manual 1987 for your car, but are rare.
no PDF books in 1987 zero
the 4th kind of 4wd, is what I call "quasi full-time 4wd", with no center differential at a,ll but has center slip clutch aka a viscous coupling
but is real nasty thing on ICE. , it slips in turns. big time! (don;'t do it)
and can go bad easy.(runs hot and fails)
;if worked before today , not 10 years ago but worked say in the last year, the vacuum parts or the switch is bad or the transfer case is dry or bad forks/rails seized , or there transfer case bad.
shorter answer,
shift devices bad (vacuum servos)
or bad transfer case, (ran it dry?)
to shift to 4wd, try it on dirt, or ice,
then shift it at lowest possible crawl speed.
1mph or less, we say a dead crawl.