i just picked up a 00 ram 1500 and it has bad u joints and the old owner had a mechanic look the truck over and he told him not to put it in 4x4. me being 16 and dumb i took her mudding anyway, got stuck since i only had it in 2hi. i tryed to put it into 4hi and it wouldnt go in and i tryed 4lo and it wouldnt go in either. i put it back into 2hi and eventuly got myself out and back to the paved road. not long after my transfer case started making bad grinding sounds, so i stopped. it took about an hour to get it to go back to 2hi. im guessing it was stuck between neutral and 2hi. it drove fine after that, besides the fact the diver side hub went. im in the process of replacing the u joints and hub bearings (having trouble getting the driveshaft nut off). im just wondering why wouldnt it go into 4x4? does it have something to do with all the slop in the u joints?

 

So does the shifter just not go into the 4x4 position, or is it in position but the front axle won't engage?

Engaging 4hi: Speed under 45mph, and shift into 4hi, take foot off gas if it doesn't wanna go in.
Engaging 4lo: Speed under 3mph, trans in neutral, shift to 4lo without stopping in neutral

If you're doing it correctly, check the fluid in the tcase. If that's all set, you may have slop in the linkage from the shifter to the tcase.

If you can get the shifter in 4x4 but the axle wont hook up, you likely have an issue with the Central Axle Disconnect assembly.

 

the shifter goes in fine but just wont engage.it was at a stand still why the truck was in neutral just idling

 

and once it started to grind the shifter tryed to push itself back towards 4hi

 

Well first thing is to check fluid before anything.
Next would be to download the factory service manual from the FAQ/DIY section at the top of this forum and read about the CAD system. Here's a flow chart for 4x4 issues:

 

I think you might have that mixed up a bit.

You can go from 2HI to 4HI at any speed up to 50 mph. Theres no neutral between the two and you dont need to shift the trans into neutral either.

Going from 2HI to 4Lo, you need to be stopped (or traveling at about 5mph or less). Put the transmission in neutral. Shift into 4Lo. Do not stop in the neutral position (on the 4x shifter) while shifting to 4Lo.

 

welcome to DF.

if you do stop in t-case neutral, simply turn off the ignition, finish the shift, and then restart the truck. it acts like this because it has syncronizers in the t-case for the 2hi-4hi shift, but not for the 2hi-4lo shift.

read and understand how the CAD works (or doesn't) because when it doesn't work, you'll get no power to the front wheels.
http://dodgeram.org/tech/repair/4X4/4x4_engagment.htm

 

Yeah I musta been a little
I edited my post to fix it.

 

Check out the link dhvaughan provided. If you are shifting correctly, that will most likely be the problem.