So I built an engine for Captain Dave about 3 years and 3000 miles ago, and it wasn't long after that he started complaining of an intermittent gear oil leak. Since it came and went I figured the drive side seal was starting to go (and given that I'd installed a Viton and my past negative experience with these things I figured that was it) so he just kept an eye on it and topped off the oil until he was ready to drop the engine and hand it back to me. Lately, he'd also been complaining of a non-functioning rear brake, and sure enough, removing the rear hub revealed brake shoes that were completely soiled with oil. Aha, I thought, the seal's done, and there's your culprit (breathing a slight sigh of relief that I didn't have to tear everything apart to replace the drive seal). Except I was wrong. Instead, I found this:
Here is a pic I dug up from the OG build 3 years ago. The bearing used is in the foreground, with the plastic cage:
The plastic cage had basically self-destructed and embedded bits of plastic all over the gearbox. Then half of the balls decided to up and leave...
When i tried to remove the layshaft, the whole bearing fell apart leaving me with this:
I am going to have fun removing that inner race from the layshaft. i see lots of heat and "surgical tapping" in my near future. Or a dremel. Suggestions welcome, by the way.
So the motto is:
1) Change your oil often and look for any bits that come out.
2) If your rear brake suddenly goes to shit, look for oil contamination among other things.
3) Pay attention to any sudden difficulty in shifting.
4) Periodically check that rear wheel/hub for wobble and play.
and perhaps most importantly
5) If the bearing has any plastic in it (apart from a seal), ditch it and move on. This could have ended badly.
Here's one more pic. Note that the gear shim has a shiny inner circle--it's actually worn a little groove in this area, due to play in the layshaft. That play also defeated the hub seal.
Stay safe out there, boys and girls.