Black powder in B4.1 Tranny

[neallewis]

I've just stripped my B4.1 transmission after loose diff issues, then gritty/notchy diff after tightening whilst racing on sunday, and the tranny was full of really smelly black powder.
It's been about 4 race meetings since I stripped it previously, and it was the same then as well, the first rebuild from new.

I'm just interested to know if this is typical, and where the fine black powder is from?

I thoroughly cleaned it with toothbrush, tissue and motor spray. There was no wear to the transmission casings. There is some tooth wear to the idler gear and diff gear, but the topshaft looks fine. The smaller bearings were all fine, but one of the larger outdrive bearings was very gritty (to be replaced). The diff was packed with more of this black powder. No wear to the ball seats in the centre gear. The diff plates were worn from the balls.

When I built it, it went together all very clean, and with just a tiny drop of silicone grease on the gears which is worked in.
I've ordered a new idler gear, and have the diff gear as a spare already.
I'm going to rebuild with as many new parts as I have, and will replace all bearings with new spares, and recycle the small bearings as front wheel bearings, as they spin fine.

Is the black powder from internal gear wear? or is it dirt passing through the outdrive bearings into the tranny? or is is slipper dust that has passed into the tranny through the top shaft bearing/ tranny case?
Any ideas?