The link I provided in the first post had a chart for testing it. Check there.

 

Update, removed actuator and tested with a vacuum pump. tested good. opened up front cover and found spider gear blown to bits. I have 3.55 rears front and back, can I put a 3.9 rear in the front

 

Front and rear gear ratios MUST be the same.

I repeat for emphasis, front and rear gear ratios MUST be the same. Otherwise, something will give.

 

Ouch... My truck was exhibiting similar symptoms. I plugged the vacuum line going to the t-case, and blocked the disconnect fork from moving over to the disconnected position. Now my 4x4 works beautifully, and my front driveline spins all the time, just like a later model.

My old Cherokee had the same problem. In both cases, it was just a bad diaphragm.

Sorry to hear about your grenaded spider gears!