722.3 Transmission Overhaul Kit Seals and Gaskets

This is the soft-parts overhaul kit for the Mercedes-Benz 722.3 four-speed automatic, the unit Mercedes builds under the internal designation W4A040. It covers 1981 through 1996 production and works behind both gas and diesel engines. Inside the kit are the paper gaskets, O-rings, rubber lip seals, metal-clad seals and Teflon-style sealing rings needed to close the transmission back up after a teardown. Manufacturer part number is K68900ADA, made in the USA by Tri Component.

The 722.3 shows up under a long list of chassis: W123, W126, W124, W201 and the R107 cars, plus the diesel sedans and wagons that ran the 617 and 603 engines. If you have a car of that era with a four-speed automatic and a vacuum modulator on the passenger side of the case, this is your kit. It is a reseal set, so it does not include friction plates, steel plates, the front band, or bushings. Order those separately if the unit came apart because of slip.

On the bench the sequence is straightforward: pull the pump, replace the front pump seal and the pump-to-case O-ring, then work through the clutch drums swapping the piston lip seals and the sealing rings on the input and center supports. The rear extension housing seal and the governor cover O-rings go in on reassembly, and the pan gasket goes on last. Every one of those pieces is in the box, which is the point of buying a kit instead of chasing individual seal numbers.

The failure this fixes is the one every 722.3 eventually has. These transmissions leak from the front pump seal, the rear extension seal and the shifter shaft seal as the rubber hardens with age, and a hardened front pump seal will let the converter weep down the bellhousing until it looks like a rear main. Hardened clutch piston seals cause the other classic 722.3 complaint: a delayed or flaring 1-2 shift as pressure bleeds past the piston instead of applying the pack. Fresh seals restore apply pressure and stop the leaks in one pass.