yes there is--its called a vsv(vacuum switch valve, i believe). it's on the front axle and has about four vacuum hoses going into it. what happens is it seizes up and the vacuum isn't enough to push the shift mechanism into 4x4. you can move the fork over manually(take it apart) or you can figure out which hose pulls it over and bypass the valve. these would be temporary fixes only, and then you should put a bolt into the inspection hole (allen plug in middle of assembly) which will press lightly on the yoke and keep it from slipping out until you make full repairs. the valve assembly will fit in a pack of cigarettes and costs just $138.00 <img src="/forums/images/graemlins/scared.gif" alt="" /> at St Chas isuzu. it's not an uncommon problem. shut the car off and then turn the key on and have someone shift in and out of 4x4. you'll hear the valve clicking and be able to find it by the noise. it's on the front driver's side of the front axle. if you need more help, i suggest searching on this issue and/or getting a haynes manual.