Originally touted as the “maintenance free” transmission by Mercedes, the 5-speed automatic that began appearing in the late 1990s was an excellent and versatile gearbox. The “maintenance free” title of this transmission was really a misnomer as the manufacturer eventually recommended servicing it every 40,000 miles.
The 722.6 transmission never included a dipstick but rather a locking cap on the dipstick tube that deterred the average car owner. Despite its quirks, it performed well in everything from four to twelve-cylinder engines. For this walkthrough, I will be discussing the 722.6 in a Mercedes CLS55 AMG.
Tools you will need to complete this service:
- 5mm Allen socket
- T30 Torx socket
- Mercedes-Benz Automatic Transmission Dipstick
- Narrow-mouthed funnel
- Oil catch pan
- Basic hand tools
- Brake cleaner
- Lint-free rags or paper towels
Parts you will need to complete this service:
- 722.6 transmission service kit
- Red lock pin for the dipstick tube cap (optional)
- Pilot bushing (optional)
Drain Fluid and Remove Oil Pan
I prefer to do transmission work after the car has sat overnight. This will mostly eliminate the annoying drips of ATF as I work under the car. The first step is to remove any underbody panels that might be partially covering the transmission. Depending on your model of vehicle, this will be different for everyone. These can be removed with an 8mm socket. Next, use your 5mm Allen socket to remove the drain plug. After the fluid has drained out, drain the torque converter if you wish. Drain plugs on torque converters are mostly found on the earlier transmissions, and I consider this step optional. Replace the drain plug washers and reinstall.
Use a T30 torx socket to remove the six pan bolts. I prefer to remove five bolts and then use my hand to support the pan as I remove the last one. This eliminates the unpleasant mess that occurs with a transmission pan splashdown. Pull straight down on the filter to liberate it and more fluid. This is a good time to check for burnt fluid or metal debris that indicate a damaged transmission.
Replace the Pilot Bushing
This step is optional. The pilot bushing is the electrical connector on the passenger side of the transmission that tends to leak. Mercedes made three different versions of the sealing rings in order to remedy this problem. To replace it, the first step is cleaning up the area with brake cleaner in an effort to improve cleanliness. To release the electrical connector, you must pull the releasing lug downwards. I have had good luck using a flathead screwdriver. It’s just too tight to use your fingers alone. Next, you will need a 7mm socket and a short extension to undo the screw in the center. After that, pull it out and be sure both sealing rings have been accounted for.
To install, lube the seals with ATF and press in the new pilot bushing, being sure the pins are aligned correctly. The bushing must be pressed in just past flush of the transmission case. Tighten the 7mm screw just past finger tight. DO NOT OVERTIGHTEN THIS! The screw is threaded into soft brass and strips easily. If you damage this, you will have a hard time getting it out and will have to replace the entire conductor plate (an expensive headache).
Clean Surfaces, Replace Filter, and Install the Pan
Fill Transmission and Test
Add four quarts of fluid through the dipstick tube and start the engine. Some fill tubes are hard to reach, and that's where a long-neck funnel comes in handy. Run through the gears in this order: P-R, R-D, and D-P. After a minute or two, check the fluid level with the special dipstick. There are two sets of markings on the dipstick. The fluid level must be between or close to one set. The upper is for a warmed up transmission, and the lower is for a cold transmission. Add fluid if necessary. After this, check for leaks and lock the dipstick tube cap on if you choose.
That's it, you just serviced the last of the DIY-friendly Mercedes-Benz transmissions! If you have any questions or suggestions, you can leave them in the comments below. And, if you found this service guide useful, you can see more at mercedes.fcpeuro.com or subscribe to our YouTube channel for additional guides on video.