Differential Case Connected With Transmission?

[felixcat]

My car is a 96 ES. In the maintenance manual, it states that the transmission and differential are separate units, so I suppose the transmission case and differential case are two closed systems, which means the ATF of differential will not flow into the transmission case, and the same for the ATF in transmission case.

But today when I went to my mechanic for a complete transmission + differential fluid flush. The mechanic removed both the drain plugs of the transmission and differential. After that, he wanted to refill the differential case first. He poured some qts of ATF into the differential's fill hole, expecting the overfill extra fluid will come out from the fill hole -- but to our surprise nothing came out!

So my mechanic checked the transmission case and found the extra ATF has already flowed into there, which means the differential and transmission are connected, and each other's ATF are exchangeable. This seems somewhat confilcting with the maintenance manual. So is there anything worng with my car or it is normal?

[wwest]

My car is a 96 ES. In the maintenance manual, it states that the transmission and differential are separate units, so I suppose the transmission case and differential case are two closed systems, which means the ATF of differential will not flow into the transmission case, and the same for the ATF in transmission case.

But today when I went to my mechanic for a complete transmission + differential fluid flush. The mechanic removed both the drain plugs of the transmission and differential. After that, he wanted to refill the differential case first. He poured some qts of ATF into the differential's fill hole, expecting the overfill extra fluid will come out from the fill hole -- but to our surprise nothing came out!

So my mechanic checked the transmission case and found the extra ATF has already flowed into there, which means the differential and transmission are connected, and each other's ATF are exchangeable. This seems somewhat confilcting with the maintenance manual. So is there anything worng with my car or it is normal?

While not truly the case, think of the transaxle and diff'l as having separate sumps, but connected above the high point of the transaxle sump. Thus the diff' must be drained separately but is refilled via the transaxle "fill".