Selec Trac 4X4 problems

[maxmillertime]

I have a 1996 Grand Cherokee with 4.0 and selec trac. This system should be shift on the fly between 2 wd, full time and part time. The problem is that when I shift it into full time (safe for dry or wet roads) the full time light comes on but it goes into part time (low speed, slippery roads only). If I try to shift back into 2wd it will not go back in easily. I have to continuously go forward and back sometimes for 5-10 minutes. It never seems to actually go into full time either. I just got this back from the shop and they replaced a u joint on the front axle which they said fixed the problem (obviously it didn't) I have been searching the internet and found that others have had the exact same problem as mine and it is fairly common but I can't find any solutions. Can anyone help?

[jeeperphil]

I just rebuilt one of these. I can't think of anything inthere except the differential that would cause this. the main gear in it has a brass spacer fixed to it. possible it's worn and the gear assy has lost its spacing causing the mode gear to not properly engage. only other thing i can think is a snap ring on either end of main shaft broke. the entire main shaft could be shifting inside the case. good luck. doesn't sound cheep. My local dealer charges 200 dollars labor to open and replace one part. differentials cast about 250. not including dropping the case.

[Meat_Shield]

i got an '02 with select trac and i had the SAME problem. instead of going forward and back...just floor it for like 2 secs the completely let off it, you might even hear the click as it goes into the desired spot. just keep doing it till it clicks in. (usually only like 2 or 3 times. hope that helps