ORIGINAL: scarletboa
it is likely a set screw in your rear center dogbone. the same thing happened twice to me with my nitro savage. some blue loctite will fix that.
it could also be one of the rear dogbones either missing, or broken.
None of the rear axles where broke or missing, rear center driveshaft is fine and grub screw is still in place. I put the diff back in and the bevel gear is warpped. It is real noticeable when you spin it in the diff it makes contact and then no contact...