My 1987 GMC s15 automatic 4x4 pickup keeps popping out of normal gear. The only gear it stays in is 4 low. Where do I start?

SOURCE: 1987 gmc s15 2.8 litre. Clutch only goes half way

I don't know that specific vehicle, but if its a hydraulic clutch it sounds like either you have a leak and your clutch fluid is low, or the master or slave cylinder could be bypassing internally. Check the fluid level in your clutch master cylinder. If its low, you should top it off with brake fluid and will probably have to bleed the system. Also look for leaks. You can probably find info or a video online of how to bleed the system. Its a bit hard to explain without illustrations or pictures. Not really very difficult to perform. Good luck.

SOURCE: replace u joint on GMC S15 pickup

You'll need a bench vice for this. A few sockets help as well. Once you get the shaft off the truck, put a smaller diameter socket on one side and a much larger diameter socket on the other and sandwich in a vice. Compress vice to drive the U-Joint through shaft (smaller socket will drive the one side through the other with the much larger socket). Installation is the reverse of removal.

SOURCE: I need manual for 1987

the best thing for you to do is stop by your local library and get your hands on a Haynes auto repair manual for your truck wish you the best of luck Michigan Man.also like to give you this information if you every have any hard to find GM-parts its Schram auto & truck parts they only sells GM- parts 1-800-292-1032 and they website is www.schramauto.com

SOURCE: I have a 1989 GMC

There are transfer case vacuum switches. The button type that you have incorporate a motor at the front differential that pulls a fork in to lock it into 4 wheel. Go in neutral then try shifting and see if its comes out of 4WD .-------- Other possibility can be locking hubs getting stuck-up hard.-------- will need to be driven in a straight line in reverse about 50 feet to completely disengage the hubs. When you stop from your reverse drive, hit the brakes a little harder than normal; this helps to "unstick" hubs sometime. If you have manual hubs, you need to disengage them on your wheel hub. ------------ Sometimes driving in reverse for 50 feet will do it. Sometimes shifting into 2wd then shifting from D to R then back to D will do it.You just have to play around with it. If that doesnt help then check the linkage.The shift linkage is got stuck hard and needs to be released.--------- Try getting under it and move the lever manually.... have someone move it from 2wd to 4wd and see if it moves.If it does, try moving it further to 2wd - it should move some more, also there is an adjustment on the shift linkage, it may need to be adjusted one way or the other.....

You might try unhooking the lever at the t-case and shifting into 2wd from there and see if that works properly.If the truck has been lifted any the shifter may be out of adjustment.Try readjusting it to 4wd low and see if it gets out of 4WD.----------
But if this is not helping, then its 4WD switch problem.-------- The switch on top of the transfercase that the actuator wires plug into was damaged. Pull that switch out and inspect, if any wire got loose or switch itself got dirty/ loose.Then remove it , clean it and connect it tight and check.----------If not helping,then switch needs to be replaced.-------Check the front axle engagement switch located in the front console.Also check 12 volt at the front axle actuator and see if its giving voltage or not.--------- This will help.Thanks.Helpmech.