The short version is this: Installed an Eaton Posi in my truck this fall about 500 miles ago. After A LOT of research I opted for Motorcraft 75w140 oil with 4oz of Motorcraft FM. Was experiencing heavy clutch chatter, so just this week I finally added another 4oz of FM. Eaton tech support had recommended starting with 4oz and titrating up while the pdf owners manual states start with 1.5oz of FM per quart of oil.
Anyways, when adding the FM the diff was very full and leaked oil out of the fill plug, so I suction gunned about 10oz out before adding the FM (and of course squirted the oil back in). Anyways, what I noticed was interesting. The gear oil had turned QUITE dark, much darker than even the original with 80k miles on it was. With little grey particles in suspension. The magnet had a few pieces of metal stuck to it, but nothing concerning. I suspect this fluid color was due to posi break in of mostly the clutches, as well as the spiders and I also have new carrier bearings at the same time.
As far as break in oil, all the info I can find really relates that to replacing the r&p, and nobody really talks about if you replace just the carrier bearing and diff. Even the Eaton instructions omit any mention of break-in oil change.
I'm 100% sure that dropping the fluid and replacing won't hurt, of course... but I have a busy life and could go without the extra task and extra cost. Can anybody present reasons or an argument which would actually support leaving the gear oil in there? I would love to do that
Anyways, when adding the FM the diff was very full and leaked oil out of the fill plug, so I suction gunned about 10oz out before adding the FM (and of course squirted the oil back in). Anyways, what I noticed was interesting. The gear oil had turned QUITE dark, much darker than even the original with 80k miles on it was. With little grey particles in suspension. The magnet had a few pieces of metal stuck to it, but nothing concerning. I suspect this fluid color was due to posi break in of mostly the clutches, as well as the spiders and I also have new carrier bearings at the same time.
As far as break in oil, all the info I can find really relates that to replacing the r&p, and nobody really talks about if you replace just the carrier bearing and diff. Even the Eaton instructions omit any mention of break-in oil change.
I'm 100% sure that dropping the fluid and replacing won't hurt, of course... but I have a busy life and could go without the extra task and extra cost. Can anybody present reasons or an argument which would actually support leaving the gear oil in there? I would love to do that