Your problem lies in you have an E-series (most likely) and an E-series transmission. The CV axle you grabbed from the Pulsar NX was either for a GA-series or CA-series. That is why the length is different, and the spline count. You'll have to get one from an E-series Sentra or Pulsar, pre-1989. Hope that helps. You might be able to use the halfshaft itself, but use your original CV axles (both ends). Usually, it is the ends that go bad, not the halfshafts, though.