BenzWorld Junior Member
Date registered: Jun 2019
Vehicle: 1998 ML320
Location: Springfield, MO
Mentioned: 0 Post(s)
Quoted: 8 Post(s)
1998 ML320 transmission questions
I'm new here, and new to working on Mercedes-Benz vehicles, but I've done quite a bit of car repair on everything from a 1930 Ford AA truck to a 1992 BMW 318iC. I recently picked up a 1998 ML320 in pretty good shape (and with a great running engine) for very little money, with the caveat that it has a transmission problem. I did my research before buying the car, and I've read up on the electrical gremlins that are known to plague the M-class 722.6 transmissions. However, I have yet to find a thread that gives me a starting point on my particular set of symptoms. My local junkyards have a number of W163 M-class donors, only one of which was tagged as having transmission troubles. They also have plenty of other Mercedes of similar era, along with non-Mercedes vehicles that used the 722.6.
Symptoms and relevant information:
*It won't move much. Specifically, in any shifter position other than park (including neutral and reverse), it tries to move forward. Very, very slowly, and with basically no torque, no matter the engine RPM. It behaves the same in any shifter position that is not park. With the engine not running, it will shift into neutral with no problem. In park, it stays put.
*The shifter moves and illuminates the selected gear normally. As noted above, it will go into neutral with no issues as long as the engine isn't running.
*There are no weird noises generated when the engine is running, no matter the RPM or shifter position.
*There are no error codes coming up on my code scanner.
*The battery is virtually new and my multimeter says that it's putting out around 14 volts.
*The previous owner said that it was running fine until it fell out of gear on a hill. It was his daughter's car, and she wasn't particularly fond of it, so he decided to let it go without further attempts at diagnosis. Her brother is a mechanic at the local BMW dealership, and gave it a going-over when they bought it.
I have the special dipstick but have not yet checked the transmission fluid level, nor have I dropped the pan or filter to take a look at quality of the transmission fluid.
As previously noted, I plugged in my OBDII scanner, and it recognizes the vehicle properly, but it appears that no error codes are being generated or are saved in the system.
If anyone has any possible diagnosis or troubleshooting suggestions, especially given the lack of error codes, it would be greatly appreciated.
I know the 722.6 was used in a large number of M-B and other vehicles for quite a few years, but I don't know anything about variations in internals, control systems, or gear ratios. Are there any particular years or models that would be a better source of parts?