Automatic Transmission: Not a Magic Box
Jerry Cole, Technical Advisor
You have had that old 190E, 240D, 300E or whatever, forever. The model doesn't really matter as much as the fact that there are pieces of toy debris under the back seat from your kids in their car seats and scrapes in the fenders from when those same kids grew up and learned to drive. You have had that old Mercedes a very long time and it has seen it all. The resale value is negligible, but it doesn't matter; it's part of the family. Then the transmission fails and needs to be rebuilt.
The transmission shop gives you a quote of $3000 or more and that meets or exceeds the value of the car. I guess that means it's time to part ways
with your old friend, right? Not so fast. If you are reading this, you are probably a DIY and an automatic transmission is not a magic box. If you would tackle an engine rebuild, given the parts and proper instructions, an automatic transmission is not much different.
Back in the 1990s, I arrived home in Washington State from New England, where I was last stationed in the Navy. When I arrived, the transmission had failed in my 1984 190D. I didn't have a garage yet, so I had to let “the professionals” do it. I took it to an independent shop in Tacoma. $3000, 18 tries and one year in, they still didn't provide a fully functional
transmission. In 2001, the transmission had failed again and they had succeeded in weaseling out of the warranty. Now what? I'll tell you what. By that time, I had a garage and an attitude. The way I saw it, in the worst case, what was I going to do, break it? It was already broken. After just a little research, I found that I could buy the ASTG manual for the transmission, a rebuild kit and the fluid to refill it for a few hundred dollars.
Removing the transmission is simple enough. As always, be certain to use jack stands and block the wheels, understanding that once you disconnect that driveshaft, it doesn't matter that you have the car in park anymore. It's brakes, jack stands and wheel chocks that are preventing the car from moving.
The trick to a successful transmission rebuild is to be cleaner than you ever have before, then be even cleaner. You remember that irritating 3mm pebble that brought your shopping cart wheel to a complete stop until you backed up and went around it? The same thing applies here, but on a much smaller scale. A simple piece of sand can prevent the valve body from operating properly. Be very clean, I can't stress that enough. It's not as hard as it sounds.
There is an intimidating list of special tools listed as required. Most of them can be worked around. The only special tool I bought for numerous Mercedes transmissions is a special socket for the tail shaft nut. Figure out what type of socket applies to the transmission you are rebuilding and buy it or modify an existing socket as necessary. If you have a decent tool set, this will probably be the only tool you'll need to buy.
Next, take high resolution pictures of everything. Lay things out in the order that you pull them and create your own exploded view. You will find that your pictures will be as valuable or more than your manual. Digital “film” is free. Take lots of pictures.
Two things worthy of mention here: First, I used a ball peen hammer with the head wrapped in cloth to compress the springs as I installed the clutches. I pressed on the cloth covered hammer head with my chest, keeping both of my hands free to manipulate the clutches, spacers and retainers. This eliminated the need for the most expensive special tool of all, a specialty compressor. Second, researching the rebuild parts for the valve body assembly, I found that it was cheaper to send it off to a valve body rebuilder, than it was to do it myself. I sent it off and it came back very quickly, done to perfection.
Most of the process is pure common sense. Did I mention that cleanliness is important? Follow the manual and reassemble it opposite the way you took it apart. Refer to your pictures often. If a part is worn out, replace it. It's as simple as that.
Once you have the transmission reassembled and reinstalled, take your victory drive in your old friend. Take pride in the fact that a little work on your part, probably kept your car from taking it's final ride to the scrap yard on a flatbed truck.
Just for the record, I have a photo of my son at age two, standing next to that 190D in 1988. I rebuilt the transmission in my garage in 2001. Still looking and driving very much like a new car, I gave my son and his new bride the car as a wedding gift in 2007, so they could start their family with it. At the time of this writing in the fall of 2014, they have two daughters, they still have the car and that transmission still works perfectly. Yes, it's worth it!