I have a big bear 400 , 2000. Yfm40fmgr according to the tittle. What is the difference between yfm40fbw. The service manual I bought says YFM40FBW on the cover. Can I go that manual ?

 

Yamaha have a very strange model numbering system, basic number YFM40 is followed by the letter system which alters with every modification, so the further the letters are away from each other the more mods there have been, but each mod may be tiny, like a different make of CV joint on the front driveshafts, and may not alter how you work on the machine at all. Or could be the difference between IRS and swinging arm, which does alter how you work on the rear end. Best thing, as you already have the FBW manual, is use it, and go for a different one if you find something that you can't fix without another manual.