true...I only let it spin for a second or so, so maybe the center diff just didn't have a chance to lock up?

 

Dorrington

Was the car making any forward momentum while the front wheel was spinning? Did you have the Ebrake engaged while you were starting out on the hill?

 

You don't have an auto by chance do you? Cause there is a fuse you can remove to make an auto one FWD and if it blew it would cause it to be FWD and then it could unload like that.

Regardless, a viscous diff does not work like an off on switch. It should be sealed and filled with a certain weight oil, very thick oil. Anyway, when the internal gears spin slowly as in when there is even wheel speeds, there is little resistance. The faster the gears try to spin, the more resistance builds and it tries to force the no spinning wheel to spin and it slows down the faster spinning one. So it transfer power to the gripping wheel. It does this very proportionally. Normally, there is fairly even traction for all wheels, so there are most likely to break traction at the same time and very evenly. If one wheel or side slips, it can only spin so much faster then the other and if there is little difference in tracion, the other wheels should break traction right away.

Now in this case, there is extreme load on all four wheels. And it should act normally, unless one front wheel has a large degree less traction then the others. It would have to be something like that one tire is in mud and the others on pavement. Now normally, the one wheel spinning in the front will transfer torque to the rear and try to slow the front. But if there is enough load, as in a very steep hill, it may be easier to have the one wheel spin.

This would be a very extreme situation though, close to having the car strapped down, and having the one wheel on rollers. So I would guess that you having an auto with a blown fuse, or there being low oil in the center diff would be more likely since you said it was a little incline, but I don't know.

I have never had this happen to me, if any broke loose, it was all four.

 

It's a manual and the e-brake was not engaged. The front wheels were on the driveway, the back on the street and ONLY the front left was spinning. My girlfriend got out and looked, said the back wheels were definitely not moving. I went back today and replicated the situation. This time, I let the wheel keep spinning for a bit, and the car ever so slowly pulled forward while the wheel spun. About 2.5 seconds and 2 feet later, the car grabbed. I'm not sure if it was the diff locking together, or if it was the front wheels grabbing the normal black tarmac above the driveway, though. Maybe the diff needs oil?