1988 Chevy 4X4 front differential won't lock up !!
 

I have a 1988 Chevy 4X4 and the front differential won't lock up.
The transfer case shifts into 4 hi and 4 lo fine its just that the auto hubs wont lock the driveshafts up front. The front driveshaft spins, just no power transfered to the wheels, it just free spins.
any suggestions would be appreciated.
Thanks

front
 

If you have the front independant suspension, more than likely your thermal actuator is bad. This is common. You can verify this by checking to see if you have voltage going to the front dif where this actuator screws into the side of the pumpkin. There is also an aftermarket version available that is manual, whereby you pull a cable that slides a plunger which replaces the original electric actuator. It is called posi-lok. The 88-93's were slow in engaging. They then went to a hi speed actuator after that. good luck