Hello; I own a 1983 300SD Turbo Diesel with over 300000 miles but still in mint condition in and out. Just now I noticed my baby doing something funny:
When I accelerate, the automatic tranny will shift from 1st to 2nd with no problems. As I continue to accelerate, just before the tranny goes into 3rd, it makes a sound for just a second that's similar to pushing the gas pedal in neutral. Then with a bit of a jolt, the tranny shifts into 3rd. It only does this on acceleration and not every time, just so now and then. Any suggestions what that could be and how I can fix that? Thank you for your response. By the way I checked all fluid levels and they are OK.

You are referring to a common problem in older transmissions called "flaring". It's quite common on the 2-3 shift. The first line of attack is to attempt to reduce vacuum slightly to the VCV. Do a search on my name and "VCV" and do some reading on how to accomplish that.

That should solve your problem temporarily............and, if not, the Superior shift kit has shown to provide significant relief for this issue.

Thank you sir. Much obliged.

Thank you sir, much obliged.

Try a can of Trans-X....