722.6 Transmission Master Rebuild Kit, Mercedes 5-Speed

This is a full master overhaul kit for the Mercedes-Benz 722.6 five-speed automatic, the unit Mercedes builds as the W5A580 and Chrysler sells as the NAG1. It covers build codes 722.621 through 722.649, so it spans the whole run of the box from the late-1990s W210 E-Class through the W203, W211, W163/W164 M-Class, the G-Class, the Sprinter 2500 and 3500 vans, and the Chrysler/Dodge/Jeep applications that share the casting. In the box: the complete overhaul gasket and seal set, the friction plate set and the steel plate set, plus the O-rings, lip seals and metal-clad seals you have to replace once the case is split.

The 722.6 is the transmission that put the phrase "limp home mode" into every Mercedes owner's vocabulary. What actually lands one on the bench is usually the same short list: the B2 brake band and the K1/K2/K3 clutch frictions worn down until the 2-3 or 4-5 shift flares, the overdrive clutch glazed from a slipping converter, hardened piston lip seals that bleed apply pressure so the unit engages late when cold, and an internal leak past the shift piston seals that shows up as a long delay from reverse into drive. None of that is fixed by a fluid service once the friction material is in the pan.

Two things to know before you order. First, the 722.6 is a build-code transmission: the plate count and clutch stack changed across 722.621 to 722.649, so read the build code off the tag on the bellhousing or the case rather than going by model year, and compare the plates in the kit against what you pulled out before you assemble. Second, the electronic side of this transmission is separate. If the car is throwing shift-solenoid codes or dropping into limp mode with no slip, the fault is far more often the conductor plate, the 13-pin connector adapter or the speed sensors than the frictions, and this kit does not include those parts.

On the bench: soak the new friction plates in clean ATF for at least 20 minutes before they go in, set each clutch pack clearance to the factory spec with a dial indicator dry before you close it up, and use the correct MB-approved fluid on refill - this box is sensitive to fluid spec and will shudder on the converter clutch with the wrong ATF. Replace the filter, and flush the cooler and lines before the rebuilt unit goes back in the car so old friction debris does not come straight back through the valve body.