Sure Grip or not

About the only way to tell for sure is to pull the center section and have a look at the unit. Sometimes, even without a sure grip, if the car is nice and level, on a flat surface, you can get both wheels to spin a little.
Also, check the bolts that hold in the center section and see if there's any type of a small metal tag attached to one of them. That may give you a little more insight into what you actually have for gears, etc.