This is a continuation of this thread:
My Custom 1980 W116 300SD Project which documents the refurbishment, maintenance, and mild customization of a daily driver 1980 Mercedes-Benz W116 300SD. I am resuming progress on the vehicle after taking a long pause during which I was working many hours while suffering from a life-long sleeping disorder that makes working full time impractical. I am once again unemployed and now have time to work on the car again. Despite a long period of no maintenance and a 2+ hour commute each day in brutal Arizona heat, it didn't let me down.
Since my last post, I attempted to seal up some leaks in the transmission. My 722.120 transmission had leaking piston cover O-rings, even though I have paperwork showing it was rebuilt in 1991. I read that while it is possible to replace the O-rings in the B2 and B3 piston covers simply by pressing in with your hands, the spring pressure in the B1 piston cover is too great.
A special factory tool is recommended my Mercedes, but the transmission must be removed from the vehicle since it takes a lot of room, and there is only 70mm (3") of clearance between the transmission and the tunnel. I have heard that it may be possible to use this tool with the transmission still in place if the exhaust pipe and driveshaft are removed, and then the transmission is lowered down as far as it will go. This is a lot of work.
I don't have a lift and doing the above would have been difficult. Feeling that I'd rather just pay someone else to do it, I called an independent Mercedes-Benz repair shop asking how much it would cost. The shop said that it would be too difficult for them to do, and they referred me to a place that specializes in German transmissions. I called the transmission shop, and the mechanic said that he wouldn't do the job without completely removing the transmission from the vehicle. This would have been expensive and would have put me without a car for a few days.
So, I decided to make a tool that would allow me to replace all of the piston O-rings with the transmission still in place and without having to lower it or remove any other parts, because that is just too much work.
CAUTION: If you make your tool any less stout than I have made mine, it will probably fail and you will not be able to finish the job. Use your ingenuity and good judgment.
I bought 3/4" hollow square steel tubing at my local hardware store. Solid aluminum bar would work as well, but it is harder to find. You need at least 14" of it--more if you make a mistake. I cut the long piece to the length of the transmission (235mm), and the short piece 120mm.
I got some 30mm long bolts the same thread pitch as the ones for the transmission pan and drilled a couple holes for them in the tubing. The holes need to be offset all the way against the edge on one side. This is to clear the valve body, and you may still need to grind a little material away at one edge (it starts at about 80mm in from the right side to about 90mm in, if you look at the picture above). The center of the bolt hole on the left side is 12mm in front the end, and the center of the right bolt hole is 21mm from the end. The center point of each should be spaced 202mm from each other.
I used a 4" long bolt (about 3/8" thick) with a thin locknut going through the center of the tubing. The center hole for it is 107mm from the right. The stronger the bolt, the better. Even this one started to bend under the spring pressure.
I drilled a hole through the short tubing so it would go through the bolt. The tubing will crush during use and cause a big disaster if you do not reinforce the hole with round tubing. I had to buy a long piece of 3/8" ID round steel tubing, cut, and grind it just small enough to slide into the square tubing. It keeps the tubing from collapsing and from it catching the threads and binding. You must do this or just use solid bar stock for this piece.
Then I drilled a long, slotted hole at the other end of the short square tubing so I could attach a 23mm socket. I put a thick washer inside the socket and then used a bolt going through it, with a locknut on the inside of the tubing. I tightened it just enough for it to stay in place, while still being able to slide as needed.