I have an 89 Jeep Wrangler and have recently discovered the vac lines coming from the front differential are broken. I have since pieced those things back together and still can't tell if four wheel drive is engaging. The light on the dash doesn't come on anymore(imagine that) but the front driveshaft is turning. I don't have a vacume pump to test the pressure coming out of the shifter motor to see if its bad at the front axle. Is there any other way to tell if this thing is engaging and pulling or just spinning the driveshaft and not engaging?