For Leistungsstellung, I would suggest "Power setting". See if any of the following URLs contain info that might be useful:
cozy.canard.com/mail_list/topics99/engines.txt
www.twindisc.com/p_mt.htm
skyraider.org/hook/tostuff.html
www.primenet.com/~kj/TFZ.htm
Pumpenrad (Drehmomentwandler, hydrodynamische Kupplung) = impeller

also pump [wheel] (pract. coll)
or
drive torus (thsc)
Treibendes Schaufelrad, das mit der Kurbelwelle über die Mintnehmerscheibe und den Wandlerdecckel verbunden ist und den Ölstrom im Wandler erzeugt)
[Pons WB Kfz-Technik]

See the following examples and URLs (from about 700 hits) for further info:
As the impeller spins, it slings automatic transmission fluid at the turbine, and ...
members.aol.com/carleyware/library/gloss3.htm
converter is filled with
transmission fluid that is moved by the impeller blades. The stator's ...
www.dakine.net/automotive-technical/automotive-technical-dr...

HTH!