725.0 9G-Tronic ATF Fill Adapter and Drain Tool Kit

Seven-piece fill and drain set for the Mercedes-Benz 725.0 nine-speed (9G-Tronic). These boxes have no dipstick and no top fill point - the fluid goes in through a side port on the pan, uphill against gravity, so you need an adapter that threads into that port and holds a hose without weeping. The kit covers the standard M12x1.5 fill adapter, a dedicated 9-speed adapter, a hybrid-specific adapter, the drain and fill plug bits, and a wrench. OEM equivalents: 725 289 22 90 00, 725 589 00 09 00, 725 589 02 90 00.

Bench sequence is straightforward once you have the right adapter. Car level on a lift or four stands, engine cold, pull the drain plug and let the pan empty. Reinstall the drain plug, then thread the fill adapter into the side port and pump new ATF in until it runs back out. Start the engine, run through the gear positions with your foot on the brake, then bring the fluid up to the check temperature (roughly 45 C on the 725.0) and top off until it just trickles out of the port. Pull the adapter, install the fill plug, done. Skipping the level-at-temperature step is what leaves these transmissions either overfilled and foaming or low and flaring on the 2-3.

Fitment is broader than the name suggests. It covers the 725.0 in the current C-Class, E-Class, S-Class, GLC, GLE and GLS, both hybrid and non-hybrid, plus the Nissan and Infiniti applications that use the same nine-speed - Nissan Z (RZ34), Frontier (D41), Titan, and Infiniti QX80. The 8-speed bit and wrench combo in the set also fits common ZF eight-speed fill plugs found on BMW, Audi, VW, Dodge, Land Rover and Toyota, so one box handles most of the sealed-for-life work that comes across a modern bench.

Adapters are zinc alloy for thread wear; the pieces that seat against the case are aluminum, which is softer than the aluminum pan itself and less likely to gall a port if you cross-thread it on the first try.