I recently read a post stating that a 400ex rear axle is shorter than a 250r's rear axle by about an inch. After replacing my 250r's rear axle with my old 400ex axle I have found that statement to be incorrect. Yes the actual axle is about an inch shorter. But the 400ex rear hubs are over an inch longer than the 250r's hubs, thus making the overall length of the axle longer than the 250r by over an inch. I was very happy that everything fit perfectly and that I didn't have to buy a new 250r axle. And gaining the extra width was just a bonus. Just thought I'd share this info with you.
One more thing, I had to use my 400ex locknuts on the axle, the 250r's were a little too long.
Dave