The truck is a 1957 3100 with a 4 speed floor shift Muncie SM420 transmission. The previous owner had transmission issues and installed a rebuilt transmission which I believe came from a '59. (59 printed in yellow paint on the case) Lots of issues repaired on the truck with the help of the forum. Lots of short round-the-block trips taken. Yesterday was the first day for a 20 mile trip to see how the truck was doing. According to the rebuilt speedometer we hit about 50 mph. All seemed good. Pulled into the driveway and a small puddle of transmission 90w appeared. Then pulled it into the garage with my intent to check it out today. Large puddle (12" x 8") under the transmission. It was not engine oil. Smelled like 90w and was clear. Coming from the front of the transmission. So off I went looking for availability of a front seal. From what I read, the 420 does not have a front seal. Correct? But I also saw a note that later ones might have had a neoprene front seal. So, does anyone know at which casting number, or even year, that a neoprene seal was used? Also, if this transmission is not supposed to have a seal, what has worn, and what is the remedy? I hope there is some good news out there. Thanks in advance!
