[Ricochet]

After fixing my exhaust yesterday at my buddy's shop I told him I want to try something.. We lifted the car a couple feet, I started it, put it in D, and only the front wheels spun. He told me something about a viscous differential, how maybe fluid has to build up before awd engagement and if the fluid is low it won't engage until giving it gas..? He told me he really didn't know so I'm asking on here now. Is this totally wrong?