I have a 1976 240D with a 1989 560SL engine and 1987 420SEL transmission in. just installed the replacement trans after destroying the oil pump in the old 722.

put 7.7 liters of Febi fluid and a new OE filter kit in the trans. when hot and idling the fluid on the dipstick is at the top twist on the lower section of the dipstick.

slips under load in 1st, 2nd, and 3rd. gets progressively better when the car is being driven and warmed up potentially? reverse is a little more solid but still slips with throttle input. fourth gear, when engaged is solid as a rock. I can hammer down on the healthy 5.5 and no issues.

really feels to me like low fluid even though the dipstick may be reading as full.

anyone have a W126 or R107 owners booklette they can snap a photo of on that page?

I'm hesitant to add more fluid due to potentially causing other issues or damage.

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1992 850i 6 speed
1991 M3 S54B32 swap
2007 328iT/6 RWD sport wagon
1987 325E 330iZHP engine swap
2004 Vespa 200GT
1976 W115 240D getting a much bigger engine. 5.5L
1997 R129 SL600 5AT