If you must replace your ring gear in your rear differential, do you have to replace the pinion gear as well?

 

From Honda they are only available as matched sets. Even used you typically buy a gear set. I've seen a couple people mix and match, and get away with it, but the gears are more likely to need shimming, and I would think you're more likely to get drivetrain noise. Besides, if the ring is damaged, the pinion almost certainly is. You need a couple special tools and a press to replace the pinion gear, but if you have that it's relatively quick and easy as far as shop time. Much worse of a job is to replace the small needle bearing at the very end of the pinion shaft, nearly always damaged if your final drive has lived on muddy gook for very long. Most of Honda's shop manuals tell you to replace the final drive case if that bearing is bad, but you can usually buy it separately. The problem is getting it out. It has a circlip you can't get to, and I've always had to break the inner away and grind two slots in the outer race to remove it. A noisy and time consuming job. I've noticed that on some of the most recent models, the price of the whole final drive assembly has gotten low enough so that it hardly pays to rebuild them anymore, at least if you're paying shop time.