Stopped shifting into 4th gear
 

1987 Mercedes 300TD, stopped shifting into 4th gear. Today, I was driving 65mph, the RPM increased rapidly, and 4th gear stopped working. I put it into neutral, then into gear, 4th worked...then after a short distance it happened again. Three days ago, I replaced transmission fluid and put 2 magnets into oil pan since there were none by the drain plug area. Magnets were household ones that I found in my garage. Could this be a problem? May be vacuum problem? I checked the dipstick and for warm engine, it shows overflow. Can this be the cause? Thank you.

The first step would be to ensure that the fill level is correct. There is a post somewhere on this forum that speaks of cleaning out a small screen in the rear part of the valve body if such a problem happens on a 722.3xx like you have.

Adding magnets is pretty good practice.

I just removed the transmission pan and took magnets out, also reduced the oil level a bit. I disconnected the kick down switch as well to check. So far, same result. I will check the screen post. Thank you.

Is your shifter loose? Bad shift bushings could make it slip into S...just brainstorming.

It is a little loose, but I tried to shift manually at the bottom and it's fine that way. I don't believe I have S.

At same time as doing transmission service, I also replaced engine mounts and transmission mount.