Cleaning sludge out of the final drive?

So today, after a short ride to get thing stirred up, I changed my final drive oil and there was some thick black sludge attached to the drain plug. I'm worried that there's a lot more sitting in there. Is there a good way to clean the reservoir out without pulling it all apart?

 

After you warm up the machine (as you did), you could drain the cavity, refill with diesel fuel, run it on the center stand under no-load conditions for a minute or two, drain, pressurize the cavity with compressed air to blow out as much crud as you can and refill with a cheap oil. Run again for a few minutes, drain and refill with quality oil. That ought to do it.
Short of that, you can use some SeaFoam or Marvel Mystery oil as an additive (under no-load conditions mind you!) to clean out the rear diff.
Good luck!

 

That drain plug is magnetic. What you are calling sludge is probably oil soaked metal particles. Entirely normal, and they aren't in the case because they stick to the magnet (it's purpose).

Rub some of it between your finger and thumb. If it feels gritty then my guess is correct.

Sludge would feel sticky, but I can't imagine why there would be any in the final drive.

 

often the metal shavings I have found in chaincases and in the rear Diff are so fine they are smooth to the feel not gritty. You can also look at them in the sunlight as you smear it between your thumb and forefing it should have a metallic sheen to it. And yes it is normal.

 

The end of the drain plug was pretty thick with the stuff, almost thicker than the threaded part of the plug, which I thought might be a little excessive for just collected metal. It didn't feel gritty, but I didn't think to look at it in the sun (good idea though). Either way I figure it can't hurt to clean the sucker out. Thanks Robert for the rundown on how to go about it.

 

I'd listen up to the advice the fellows mentioned. If the "sludge" is fine particles like they mention, this is a normal condition and would not indicate the need for a flush. I've found the same "sludge" on my bikes and none are experiencing problems. Just perform the required maintenance at the required intervals and you should be fine.
I would only flush the system in the manner I suggested if you find the diff is filled with black oil or foreign material (sawdust?). Do bear in mind I've never had to clean out a rear diff (my experiences have to do with a Pontiac 305 lump and a VW 1600).

 

Huh. maybe i'll wait on that then, and just keep an eye on it. It could very well be that the PO just didn't change the oil much and there was a lot of build up. I certainly have enough to do to the bike without piling more on my plate. Thanks guys.