Does the ATF needs to be drained before replacing the governor pressure valve?

1992 300D, 722.418 tranny.

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.

I would so you dont create a mess

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Should I drain both the pan and the converter, or can I just drain the pan?

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.

both

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Isn't the fluid flow blocked between the converter and the rest part of the transmission?

When I drained ATF a while ago, the fluid in the converter did not come out though the drain plug opening of the transmission pan. Less than half of the liquid came out of the pan. More than half remained in the converter, and that came out though the drain plug opening on the converter.

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.

I said drain both because most likely you will be replacing the fluid and so you have new fluid in both.

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)