Are the Truck and 4Runner (1990) front IFS and rear axles interchangable? I need a front differential for my 4Runner and found a guy with truck IFS differential for sale, will it bolt on?

 

Front, possibly. As long as you both have ADD, or both don't have ADD, it would be direct bolt in. If one of you has one and the other has the other, then still doable, but not as bolt on.

Rear, yes and no. You can swap out the third members no problem, as in, if you were getting it for the gearing, but you cannot swap axle tubes without cutting and welding. 4runner has coils, truck has leaf springs.