I just purchased a 1994 ford ranger with 125,000 miles and runs great until last night when i had to engage the four wheel drive.It made a bad clunk and whining noise for some time and now i can hit the four wheel button but it doesnt engage at all. i would like to know what the problem most likely is thank you

the actuator for the hub locking is faulty and not engaging the hub correctly. There may be badly worn teeth to engage or broken parts in the hub.
Have an accredited drive line shop check it out.

I think yours has the automatic locking hubs that slide over the the rotor hub. If this is the case than what has probably happened is a u-joint has gone bad and wiped out that auto hub.

Be prepared for some sticker shock on those hubs. they are not cheap. The usual fix for this is to replace the front axle ujoints and what ever hub is making the noise, hopefully just one.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

the auto 4 wheel does the same as part time in jeeps, it engages only when the vehicle loses traction. when auto 4 wheel is on the truck isn't fully in 4 wheel drive. my 02 sierra makes the clunk noise too but it does engage. try checking your fluids, i know its way pass the time for me to change mine out.

what is the vehicle?
some trannys have a solenoid whick engages and locks 4 wheel i cant help u without knowing the details

sounds like the transfer unit is going bad check level of oil in the case if burnt then you know what it is if ,it's not burnt check the front axel to see if it is leaking

The Bendix drive is bad in the starter. You can either rebuild it or just purchase a new rebuilt starter.
The Bendix drive is what pushes the starter gear into the flywheel the then it will turn the flywheel. When the Bendix drive goes bad the starter just spins/whirls.

the transfer case is sticking from non use, change the lube in the case ( Ford ATF) and drive it for awhile it should be ok then.

Try to rock it by putting it into D an R it works for my truck.

did u hook the shift linkage back up

I have a 1994 ford f150, my 4 wheel drive keeps trying to engage by itself even without me touching the automatic hub button....at time you can even hear it engaging and disengaging by itself, the low range light even comes on (dimly)...what could be the cause? the transfer case motor looks good and so does the wiring.