I have an 84 m1009. Awhile ago it started leaking fluid really bad and noticed it was coming from my front drive shaft at the transfer case. Noticed shaft fell off and was only holding on by 1 bolt. Truck now vibrates like crazy at certain speeds. To my knowledge I thought the front shaft only engaged during 4wheel drive. Truck is not in 4wheel and hubs are free. What could cause it to fall off and why the vibrations?