I have got a 400ex and i noticed the other day the rear axle is loose. I think it might be the rear bearings have gone bad but im not sure can anyone help me out, and tell me how to fix it.

 

yup your bearings are shot. this is normally a straight forward fix. take the brake rotor(or sprocket) and hubs off one side of the axle. take off the axle nuts and pull the axle out. now you can either unblot the carrier or leave it in, your preference. then take out the old bearings and seals then put the new stuff in and reassemble. the is GENERALLY how its down and not modle specific. good luck

is the swingarm moving too if so then you need bushings for your swing arm too

 

First symptom is that your chain goes slack unexpectedly. You adjust it once, then it goes out again, and you discover that the bearings are gone.

If the bearings are shot, don't neglect them! Mine went while I was out on a very long desert ride. Had to ride back to camp...had no other choice. Toasted the bearings and ruined the carrier as well. Got expensive!

 

how many bearings and seals are there in the rear end that would have to be replaced.