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?

[neallewis]

I guess no one has stripped down their B4.1 transmission before?

It's now rebuilt with new components (plastic gears, all new bearings, etc). Lets see how long it takes to get full of the black stuff again now. It was only four race meetings after last rebuild.

The car is 3 months old, and I do keep it clean after every race meeting.

[adey]

That's very odd. Is it possible that the grease you are using is drying up in the gearbox ?. Is the transmission free spinning when built ?. Others on here may disagree but I doubt much dust would get in gearbox from racing if if it did I would expect it to take a while. For me it's either a gear binding on the Gbox, binding on each other or the grease.

[neallewis]

Originally Posted by adey

That's very odd. Is it possible that the grease you are using is drying up in the gearbox ?. Is the transmission free spinning when built ?. Others on here may disagree but I doubt much dust would get in gearbox from racing if if it did I would expect it to take a while. For me it's either a gear binding on the Gbox, binding on each other or the grease.

The transmission rotated really freely. Spinning the wheels, it ran on for ages (with no pinion).

I'd just applied a very small amount of silicon grease to the layshaft gear and idler gear, which was worked in. Only a tiny amount, it almost disappeared when worked in rotating the box before assembly. It wasn't packed with grease, and there was no grease binding the tranny.
I've left it totally dry this time i've rebuilt.

There was some wear to the idler gear teeth, and less wear to the diff gear teeth. I'm guessing the idler gear wears more as its in contact with the metal layshaft gear.

The four small bearings were all free of dirt internally and span freely. One outdrive bearing was free, the other was rough and didn't spin freely.

It ran for four meetings, two on carpet, two outdoors/grass/astro.


I've now rebuilt it, replacing the diff and idler gears, and all bearings as I had spares.

I do wonder if dirt passes into the transmission either through the bottom square in the casing that's exposed in the rear arm mount/chassis plate, or passing either through the outdrive bearings, or through the bearing seats of the outdrives. Another thought is through slipper dust through the bearing seat of the top layshaft. I wonder if a shim kit would take out any slop, or that small side to side movement of the diff and layshaft, preventing any dirt pass through? it's just a theory, but i'm puzzled as to where else it come from.

[adey]

It is strange. I ran a b4 for years and I still run a x6 which I believe has the same gears in as I b4.1 with no problems at all. Is the layshaft free from play ?

[neallewis]

Originally Posted by adey

It is strange. I ran a b4 for years and I still run a x6 which I believe has the same gears in as I b4.1 with no problems at all. Is the layshaft free from play ?

X6 has an extra idler gear in, but essentially the same.

I just checked the layshaft, now its built up. no side-to-side play with the slipper and spur on. When stripping and building it up, there was some slight movement without the slipper on. There is a wear mark, but not a ridge on the layshaft where it fits in the outside bearing.

I've just broken in my diff and checked it's adjustment. its silky smooth. Removing pinion, the tranny rotates really freely with a spin of the wheels.
I'll run it like this and inspect it again after my next outdoor meeting.