How well should a slip yoke be polished to give a proper seal?

Question

Gear oil started leaking out of the rear output seal on my '01 Outback started -- onto the exhaust of course, as every fluid in a Subaru seems to do. It's not a lot, but smells terrible.

Along with replacing the seal, I figured I would polish the slip yoke since it has over 170,000 miles on it now. There aren't any scratches big enough to catch my fingernails on it, but it doesn't look perfect.

I cleaned it up with some 0000 steel wool. It doesn't look as shiny as the clean spots did before I started. It has a satin finish now, but feels perfectly smooth.

Do I need to polish it to a mirror finish with progressively finer grits of sandpaper, or is 0000 steel wool enough?

On the other end of the spectrum, is it possible to polish it too much? Would a glass-smooth surface cause any problems?

Answer 1

I have never polished a slip yoke or felt the need to. I would just clean off any heavy dirt and just clean it up a little with the steelwoll as you have already done. Over polishing may reduce the diameter to the point that the seal will leak. Apply a light coating of oil on the yoke prior to reinstalling it. This will lube the seal for the first few turns and prevent possible tearing of the seal during installation.