Dirty differential fluid - cleaning?

Changed the oil in the rear diff of a LSD F350 last night, and the stuff that came out was pretty nasty! Nice dark red/brown color, smelled a little burnt, and most of the carrier had bits of carbon/gunk that came off with brake cleaner. Sprayed everything off as best as I could and put the cover back on. Still, I'm worried about how bad it was.

I'm not sure if its from the LS clutches or just the fluid was in there too long, but is there a way to kinda power-clean the differential in a few thousand miles? I was considering putting in cheap fluid and running that for 5k miles or so, and then changing again - would this help at all? What about ATF - I know this will clean engines real nice, but will it play nice with the clutches??

Invest in a few gallons of brake cleaner and just spray that in with the cover on until its full?

just change the fluid with every oil change a few times and then forget about it..

Unless there's metal flakes or chips, don't get too worked up. Make sure you're using the right gear lube and change it again in a few weeks. Don't put anything in there that's not recommended for your LSD. It'd be a shame to ruin the clutch plates.

If you're that worried take a sample and have it analyzed. That'll tell you whether you're making a fuss over nothing or have something to really worry about. I do that all day long and give people answers to this very same question.

In reply to Bobzilla:

All that dif fluid is now unfortunately mixed with 15qts of used engine oil I should have thought about it before I did that!

I'll go ahead and throw some cheap WM LS-approved stuff in there for an oil change and then go back to redline. Thanks all!

Sounds like it got too hot for too long (are you running synthetic in it?) and cooked the oil a bit. In any event a little bit of sludge isn't going to hurt a rear end.

ncjay wrote: Unless there's metal flakes or chips, don't get too worked up. Make sure you're using the right gear lube and change it again in a few weeks. Don't put anything in there that's not recommended for your LSD. It'd be a shame to ruin the clutch plates.

This, except I wouldn't bother with the re-change in a few weeks.

The only way to really clean everything is to take it apart and swab it out. My favorite thing for this actually is one of those ceiling dust bunny removal dealies, looks like a dingleberry hone on a longer stick and no dingleberries. Chuck that sucker up in a drill and flow some kerosene in the axle tube as you work the scrubber back and forth. Then regular parts brush inside the diff housing. But this requires complete disassembly and is something you do when rebuilding after you find metal flakes in the oil, which usually coincides with hosed and screaming bearings and a ring and pinion that are worn down to having no pattern at all.

if the rearend isn't screaming from pitted bearings (what the red color makes me think of, as that's usually rust) then I say just give it new fluid and keep on truckin' until problems come up. Any damage is done, doing any kind of megaflush isn't going to help things any.

Here's something to think about: The clutches in a friction LSD are wear items. As they wear, they get thinner, which allows the side gears to move away from the spiders. This makes the gears contact each other on the tips, not the full contact they need, so now they can break off. If you look in the manual, I think "rebuild the diff" is in there somewhere (100K miles?). Ask me why I learned all this stuff about how spider and side gears can break.

That depends on the diff type. That wear mode you descibe only exists for poopy diffs compromised for C-clip axles. A Salisbury (?) type clutch diff that separates the functions of the gears and the clutching mechanism does not have that problem.

When i was rebuilding the rear end for the stang i found a brush at walmart that was made to clean fridge coils. Picture the brushes used for washing the inside of drinking glasses, but the bristly part is 2-3 feet long. When i took it to check out the cashier looked at it and asked what it was for. "Im gonna use it to clean out my rear end." The conversation pretty much died right there.

I've had a few rear end explosions. One was really bad; the spider gears were reduced to metallic chunks and the carrier was in 3 pieces. I had to replaced the center section. But the others, after I drained the oil, I used a can of brake cleaner and flushed out the housing. I didn't spray the gearset down, just the inside of the housing. That seemed to flush out most of the chunks and crap. Then I wiped it out with a clean rag.

You'll never get it operating room clean but it doesn't need to be. It's a pretty harsh environment.

Oh, and wear eye protection. That E36 M3 got splattered everywhere. I had to throw away my clothes since I couldn't get the gear oil stench out.

stanger_missle wrote: You'll never get it operating room clean but it doesn't need to be. It's a pretty harsh environment.

This. It's amazing the levels of iron, copper and lead that are considered "normal" for diffs. but remember it's not a pressurized oiling system. It just splashes up and kinda coats everything and that's good enough.

In reply to Knurled: I just looked at an exploded diagram of the Salisbury type diff, and it appears that the clutch packs still have a say in where the gears end up.