ive got a 1996 blazer 2dr 4wd and its the ls model not zr2. when im in 4wd both my front and rear diff. lock and all foru tires spin, and today i was in 2wd flexing and my friend told me to tap the brakes to see if it did what his z71 did and when i did the rear axle locked up and both tires were spinning. my question is, is this a normal thing in blazers or a gm option or did somebody change my axles?