Just bought a 1990 montero with auto free_wheel hubs . 4 wheel drive working fine until today. 1 ft new snow. Started out in 4 lo making a path and packing down snow. Back and forth and making progress until the 4 wheel drive stopped working. What engages the hubs? I've read from the posts forward motion or vacuum engages the four wheel drive. Did I disengage the hubs by doing all the back and forth motion? Trying to figure out where to start looking for the problem. Thanks