goldbrick wrote:I've never seen a differential that specifies AT fluid for lubrication. It's usually something like 75W90 GL-4 or GL-5 gear oil, which is certainly not what you would put into any automatic transmission that I have ever heard of.
We're not talking about standalone diffs. As estomax said, for a front-drive car, you have a transaxle with a single fluid that lubricates the transmission and differential because they are in the same case. Maybe there are some rare exceptions, but nearly every manual or automatic transaxle in production vehicles will have one fluid. For an automatic transaxle that means the differential portion is lubricated with ATF.
Well, I'll be....ATF D6 is new to me but I don't agree it is a 'rare exception' that that FWD cars use different oils for the transmission and differential. Every automatic transmission I've ever seen uses AT fluid (eg Dextron, Mercon, Type F, etc) for the transmission and gear oil for the differential. This is for front wheel drive (or 4WD) cars. As Leftie said, just because the trans and diff are in the same outer case doesn't mean that they share oils. In many cases, there is a separate fill plug (often just a hex-head bolt) that is used to check and/or top off the differential oil. The main transmission fluid is usually drained from a plug on the bottom. I don't know when ATF D6 came into being or what transmissions use it but as one example, any ZF built 'tiptronic' transmission as found on VWs, Audis, BMWs, etc, etc will use both ATF fluid for the transmission and gear oil for the differential. They are in the same 'case' but they do not mix.