About a month ago, I installed a self built AutoGear M22. All gears, sliders, forks, synchros, etc. were new. The only used parts that I used were the mainshaft and the hubs. I have driven it a few hundred miles and I am quite pleased with it. I just removed the break in oil tonight and I replaced it with some Redline MT90. I noticed that the old oil (just regular 80W90, GL5 gear oil) had alot of brass particles in it, which I expected. It also had alot of very fine steel particles in it too. The magnetic drain plug was covered in some very, very fine steel particles. The particles, mixed with the oil made sludge or sorts. There were no particles of any size larger than this that I saw. Is this normal break in wear particles or is there a potential problem with my transmission? It still shifts great and runs very smooth.

Also, for anyone who is interested. The Redline MT90 made my tranny a little quieter and made it shift a little better.

I'd say it's normal.
For others reading this:
It's very important to remember when new trans or diff gears undergo break-in it creates extra friction and heat. You can overheat the gears locally, and damage their surface heat treat if you drive too long and too hard with a new trans or diff.

The recomended break-in is some easy driving with an occasional quick acceleration.

The Hewland transaxle in my race car has a $1500. ring and pinion and a temp guage. Believe me, I give it a long break in!

David