I have a 1949 Buick Roadmaster with an automatic Dynaflow transmission that had been working normally until the other day. Without warning, it does not engage in lo, drive, or reverse. All gears simply act as if it is in neutral. I had been driving it around my neighborhood recently (so a max of 25mph) with no troubles.

I have a manual of the Dynaflow transmission and it mentions the pump likely being the culprit. Are there any other areas of interest I should investigate first prior to looking in the transmission guts?

Thanks for taking the time to read,
Brian